Post by L6S on Jan 16, 2013 14:28:17 GMT -5
The Ketogenic Diet
By: Lyle McDonald
What is a ketogenic diet?
In the most general terms, a ketogenic diet is any diet that causes ketone bodies to be produced by the liver, shifting the body’s metabolism away from glucose and towards fat utilization. More specifically, a ketogenic diet is one that restricts carbohydrates below a certain level (generally 100 grams per day), inducing a series of adaptations to take place.
Basics of fuel utilization
There are four primary fuels which can be used in the human body: glucose, protein, free fatty acids, and ketones. [...] the primary form of stored fuel is triglyceride, stored in adipose tissue. Glucose and protein make up secondary sources. These fuels are used in varying proportions depending on the metabolic state of the body.
The primary determinant of fuel utilization in humans is carbohydrate availability, which affects hormone levels. Additional factors affecting fuel utilization are the status of liver glycogen (full or empty) as well as the levels of certain enzymes.
When present in sufficient quantities, glucose is the preferred fuel for most tissues in the body. The major exception to this is the heart, which uses a mix of glucose, FFA and ketones.
The major source of glucose in the body is from dietary carbohydrate. However, other substances can be converted to glucose in the liver and kidney through a process called gluconeogenesis. If glucose requirements are high but glucose availability is low, [...] the body will break down its own protein stores to produce glucose. [...] an adequate protein intake during the first weeks of a ketogenic diet will prevent muscle loss by supplying the amino acids for gluconeogenesis that would otherwise come from body proteins.
Most tissues of the body can use FFA for fuel if it is available. This includes skeletal muscle, the heart, and most organs. However, there are other tissues such as the brain, red blood cells, the renal medulla, bone marrow and Type II muscle fibers which cannot use FFA and require glucose.
The Brain
The fact that the brain is incapable of using FFA for fuel has led to one of the biggest misconceptions about human physiology: that the brain can only use glucose for fuel. While it is true that the brain normally runs on glucose, the brain will readily use ketones for fuel if they are available.
In a non-ketotic state, the brain utilizes roughly 100 grams of glucose per day. This means that any diet which contains less than 100 grams of carbohydrate per day will induce ketosis, the depth of which will depend on how many carbohydrates are consumed (i.e. less carbohydrates will mean deeper ketosis). During the initial stages of ketosis, any carbohydrate intake below 100 grams will induce ketosis. As the brain adapts to using ketones for fuel and the body’s glucose requirements decrease, less carbohydrate must be consumed if ketosis is to be maintained.
[...] the brain which can derive up to 75% of its total energy requirements from ketones after adaptation. In all likelihood, ketones exist primarily to provide a fat-derived fuel for the brain during periods when carbohydrates are unavailable.
Utilization of ketones in the body
Under normal dietary conditions, ketone concentrations are so low that ketones provide a negligible amount of energy to the tissues of the body. If ketone concentrations increase, most tissues in the body will begin to derive some portion of their energy requirements from ketones. Some research also suggests that ketones are the preferred fuel of many tissues. One exception is the liver which does not use ketones for fuel, relying instead on FFA.
By the third day of ketosis, all of the non-protein fuel is derived from the oxidation of FFA and ketones. As ketosis develops, most tissues which can use ketones for fuel will stop using them to a significant degree by the third week. This decrease in ketone utilization occurs due to a down regulation of the enzymes responsible for ketone use and occurs in all tissues except the brain. After three weeks, most tissues will meet their energy requirements almost exclusively through the breakdown of FFA. This is thought to be an adaptation to ensure adequate ketone levels for the brain.
Storing fuel
Excess dietary carbohydrates can be converted to fat in the liver through a process called de novo lipognesis (DNL). However short term studies show that DNL does not contribute significantly to fat gain in humans. As long as muscle and liver glycogen stores are not completely filled, the body is able to store or burn off excess dietary carbohydrates. Of course this process occurs at the expense of limiting fat burning, meaning that any dietary fat which is ingested with a high carbohydrate intake is stored as fat.
The most likely scenario in which this would occur would be one in which an individual was inactive and consuming an excess of carbohydrates/calories in their diet. As well, the combination of inactivity with a very high carbohydrate AND high fat diet is much worse in terms of fat gain. With chronically over-filled glycogen stores and a high carbohydrate intake, fat utilization is almost completely blocked and any dietary fat consumed is stored. This has led some authors to suggest an absolute minimization of dietary fat for weight loss. The premise is that, since incoming carbohydrate will block fat burning by the body, less fat must be eaten to avoid storage. The ketogenic diet approaches this problem from the opposite direction. By reducing carbohydrate intake to minimum levels, fat utilization by the body is maximized.
A high carbohydrate diet decreases the use of fat for fuel and vice versa. Thus, the greatest rates of fat oxidation will occur under conditions when carbohydrates are restricted. As well, the level of muscle glycogen regulates how much fat is used by the muscle [...]. Using exercise and/or carbohydrate restriction to lower muscle and liver glycogen levels increases fat utilization.
Summary: When carbohydrate availability is high, carbohydrate use and storage is high and fat use is low. When carbohydrate availability is low, carbohydrate use and storage is low and fat use is high. The most basic premise of the ketogenic diet is that the body can be forced to burn greater amounts of fat by decreasing its use of glucose.
Insulin
Insulin is a peptide (protein based) hormone released from the pancreas, primarily in response to increases in blood glucose. When blood glucose increases, insulin levels increase as well, causing glucose in the bloodstream to be stored as glycogen in the muscle or liver. Excess glucose can be pushed into fat cells for storage (as alpha-glycerophosphate). Protein synthesis is stimulated and free amino acids (the building blocks of proteins) are moved into muscle cells and incorporated into larger proteins. Fat synthesis (called lipogenesis) and fat storage are both stimulated. FFA release from fat cells is inhibited by even small amounts of insulin.
The primary role of insulin is to keep blood glucose in the fairly narrow range of roughly 80-120 mg/dl. When blood glucose increases outside of this range, insulin is released to lower blood glucose back to normal. The greatest increase in blood glucose levels (and the greatest increase in insulin) occurs from the consumption of dietary carbohydrates. Protein causes a smaller increase in insulin output because some individual amino acids can be converted to glucose. FFA can stimulate insulin release as can high concentrations of ketone bodies although to a much lesser degree than carbohydrate or protein.
Basic ketone physiology
The three ketone bodies are acetoacetate (AcAc), beta-hydroxybutyrate (BHB) and acetone. AcAc and BHB are produced from the condensation of acetyl-CoA, a product of incomplete breakdown of free fatty acids (FFA) in the liver. While ketones can technically be made from certain amino acids, this is not thought to contribute significantly to ketosis. Roughly one-third of AcAc is converted to acetone, which is excreted in the breath and urine. This gives some individuals on a ketogenic diet a ‘fruity’ smelling breath.
As a side note, urinary and breath excretion of acetone is negligible in terms of caloric loss, amounting to a maximum of 100 calories per day. The fact that ketones are excreted through this pathway has led some authors to argue that fat loss is being accomplished through urination and breathing. While this may be very loosely true, in that ketones are produced from the breakdown of fat and energy is being lost through these routes, the number of calories lost per day will have a minimal effect on fat loss.
While many tissues of the body (especially muscle) use a large amount of ketones for fuel during the first few weeks of a ketogenic diet, most of these same tissues will decrease their use of ketones as the length of time in ketosis increases. At this time, these tissues rely primarily on the breakdown of free fatty acids (FFA). In practical terms, after three weeks of a ketogenic diet, the use of ketones by tissues other than the brain is negligible and can be ignored.
The liver is always producing ketones to some small degree and they are always present in the bloodstream. Under normal dietary conditions, ketone concentrations are simply too low to be of any physiological consequence. A ketogenic diet increases the amount of ketones which are produced and the blood concentrations seen. Thus ketones should not be considered a toxic substance or a byproduct of abnormal human metabolism. Rather, ketones are a normal physiological substance that plays many important roles in the human body.
Ketosis vs. Ketoacidosis
Ketosis occurs in a number of physiological states including fasting (called starvation ketosis), the consumption of a high fat diet (called dietary ketosis), and immediately after exercise (called post-exercise ketosis). Two pathological and potentially fatal metabolic states during which ketosis occurs are diabetic ketoacidosis and alcoholic ketoacidosis.
The major difference between starvation, dietary and diabetic/alcoholic ketoacidosis is in the level of ketone concentrations seen in the blood. Starvation and dietary ketosis will normally not progress to dangerous levels, due to various feedback loops which are present in the body. Diabetic and alcoholic ketoacidosis are both potentially fatal conditions.
Under normal conditions, ketone bodies are present in the bloodstream in minute amounts, approximately 0.1 mmol/dl. When ketone body formation increases in the liver, ketones begin to accumulate in the bloodstream. Ketosis is defined clinically as a ketone concentration above 0.2 mmol/dl. Mild ketosis, around 2 mmol, also occurs following aerobic exercise. Ketoacidosis is defined as any ketone concentration above 7 mmol/dl. Diabetic and alcoholic ketoacidosis result in ketone concentrations up to 25 mmol. This level of ketosis will never occur in non-diabetic or alcoholic individuals.
Additionally, in non-diabetic individuals there are at least two feedback loops to prevent runaway ketoacidosis from occurring. When ketones reach high concentrations in the bloodstream (approximately 4-6 mmol), they stimulate a release of insulin. This increase in insulin has three major effects. First, it slows FFA release from the fat cell. Second, by raising the insulin/glucagon ratio, the rate of ketone body formation in the liver is decreased. Third, it increases the excretion of ketones into the urine. These three effects all serve to lower blood ketone body concentration.
In addition to stimulating insulin release, ketones appear to have an impact directly on the fat cell, slowing FFA release. This would serve to limit FFA availability to the liver, slowing ketone body formation. Ultimately these two feedback loops prevent the non-diabetic individual from over producing ketones since high ketone levels decrease ketone body formation.
Ketonemia vs. Ketonuria
The general metabolic state of ketosis can be further subdivided into two categories. The first is ketonemia which describes the buildup of ketone bodies in the bloodstream. Technically ketonemia is the true indicator that ketosis has been induced. However the only way to measure the level of ketonemia is with a blood test which is not practical for ketogenic dieters.
The second subdivision is ketonuria which describes the buildup and excretion of ketone bodies in the urine, which occurs due to the accumulation of ketones in the kidney. The excretion of ketones into the urine may represent 10-20% of the total ketones made in the liver. However, this may only amount to 10-20 grams of total ketones excreted per day. Since ketones have a caloric value of 4.5 calories/gram, the loss of calories through the urine is only 45-90 calories per day. The degree of ketonuria, which is an indirect indicator of ketonemia, can be measured by the use of Ketostix (tm), small paper strips which react with urinary ketones and change color.
Ketonemia will always occur before ketonuria. Ketone concentrations tend to vary throughout the day and are generally lower in the morning, reaching a peak around midnight. This may occur from changes in hormone levels throughout the day. Additionally, women appear to show deeper ketone levels than men and children develop deeper ketosis than do adults. Finally, certain supplements, such as N-acetyl-cysteine, a popular anti-oxidant, can falsely indicate ketosis.
The distinction between ketonuria and ketonemia is important from a practical standpoint. Some individuals, who have followed all of the guidelines for establishing ketosis will not show urinary ketones. However this does not mean that they are not technically in ketosis. Ketonuria is only an indirect measure of ketone concentrations in the bloodstream and Ketostix (tm) measurements can be inaccurate.
Adaptations to Ketosis
In one sense, the ketogenic diet is identical to starvation, except that food is being consumed. That is, the metabolic effects which occur and the adaptations which are seen during starvation are roughly identical to what is seen during a ketogenic diet. The primary difference is that the protein and fat intake of a ketogenic diet will replace some of the protein and fat which would otherwise be used for fuel during starvation.
During the first 3 days of fasting, blood glucose drops from normal levels of 80-120 mg/dl to roughly 65-75 mg/dl. Insulin drops from 40-50 µU/ml to 7-10 µU/ml. Both remain constant for the duration of the fast. One thing to note is that the body strives to maintain near normal blood glucose levels even under conditions of total fasting. The popularly held belief that ketosis will not occur until blood glucose falls to 50 mg/dl is incorrect.
Additionally, the popular belief that there is no insulin present on a ketogenic diet is incorrect. One difference between fasting and a ketogenic diet is that the slight insulin response to dietary protein will cause blood glucose to be maintained at a slightly higher level, approximately 80-85 mg/dl. This most likely occurs due to the conversion of dietary protein to glucose in the liver.
Although the liver is producing ketones at its maximum rate by day three, blood ketone levels will continue to increase finally reaching a plateau by three weeks. The decrease in blood glucose and subsequent increase in FFA and ketones appear to be the signal for the adaptations which are seen [...]. Measurements of fuel use show that approximately 90% of the body’s total fuel requirements are being met by FFA and ketones by the third day. After three weeks of starvation, the body may derive 93% of its fuel from FFA.
Most tissues except the brain, stop using ketones for fuel after the third week of ketosis. This is especially true for skeletal muscle. While muscle initially derives up to 50% of its energy requirements from ketones, this drops to 4-6% by the third week of ketosis.
Why do the use of ketones drop?
During the first few days of ketosis, the brain is incapable of using ketones for fuel. By using a large amount of ketones for fuel, skeletal muscle prevents a rapid increase in blood ketone levels, which might cause acidosis. As time passes and the brain adapts to using ketones for fuel, skeletal muscle must stop using ketones for fuel, to avoid depriving the brain of fuel. For all practical purposes, with long term starvation, the primary fuel of all tissues except the brain is FFA, not ketones.
All tissues in the body have the capacity to use glucose. With the exception of the brain and a few other tissues (leukocytes, bone marrow, erythrocytes), all tissues in the body can use FFA or ketones for fuel when carbohydrate is not available.
Under normal dietary conditions, glucose is the standard fuel for the brain and central nervous system (CNS). The CNS and brain are the largest consumers of glucose on a daily basis, requiring roughly 104 grams of glucose per day. This peculiarity of brain metabolism has led to probably the most important misconception regarding the ketogenic diet. A commonly heard statement is that the brain can only use glucose for fuel but this is only conditionally true. It has been known for over 30 years that, once ketosis has been established for a few days, the brain will derive more and more of its fuel requirements from ketones, finally deriving over half of its energy needs from ketones with the remainder coming from glucose.
As a few tissues do continue to use glucose for fuel, and since the brain’s glucose requirement never drops to zero, there will still be a small glucose requirement on a ketogenic diet. This raises the question of how much glucose is required by the body and whether or not this amount can be provided on a diet completely devoid of carbohydrate.
Adaptations when carbs are restricted
When carbohydrate is removed from the diet, the body undergoes at least three major adaptations to conserve what little glucose and protein it does have.
The primary adaptation is an overall shift in fuel utilization from glucose to FFA in most tissues, as discussed in the previous section. This shift spares what little glucose is available to fuel the brain.
The second adaptation occurs in the leukocytes, erythrocytes and bone marrow which continue to use glucose. To prevent a depletion of available glucose stores, these tissues break down glucose partially to lactate and pyruvate which go to the liver and are recycled back to glucose again. Thus there is no net loss of glucose in the body from these tissues and they can be ignored in terms of the body’s carbohydrate requirements.
The third, and probably the most important, adaptation, occurs in the brain, which shifts from using solely carbohydrate for fuel to deriving up to 75% of its energy requirements from ketones by the third week of sustained ketosis. As the brain is the only tissue that continues to deplete glucose in the body, it is all we need concern ourselves with in terms of daily carbohydrate requirements.
Glycogen
The initial storage depot of carbohydrate in the body is the liver, which contains enough glycogen to sustain the brain’s glucose needs for approximately 12-16 hours. We will assume for the following discussion that liver glycogen has been depleted, ketosis established, and that the only source of glucose is from endogenous fuel stores (i.e. stored bodyfat and protein). After its glycogen has been depleted, the liver is one of the major sources for the production of glucose (gluconeogenesis) and it produces glucose from glycerol, lactate/pyruvate and the amino acids alanine and glutamine. The kidney also produces glucose as starvation proceeds.
Protein and muscle loss
During the initial weeks of starvation, there is an excretion of 12 grams of nitrogen per day. Since approximately 16% of protein is nitrogen, this represents the breakdown of roughly 75 grams of body protein to produce 75 grams of glucose. If this rate of protein breakdown were to continue unchecked, the body’s protein stores would be depleted in a matter of weeks, causing death.
After even 1 week of starvation, blood alanine levels begin to drop and uptake by the kidneys decreases, indicating that the body is already trying to spare protein losses. During longer periods of starvation, blood levels of alanine and glutamine continue to decrease, as does glucose production by the liver. As glucose production in the liver is decreasing, there is increased glucose production in the kidney.
Because of these adaptations, nitrogen losses decrease to 3-4 grams per day by the third week of starvation, indicating the breakdown of approximately 20 grams of body protein. With extremely long term starvation, nitrogen losses may drop to 1 gram per day, indicating the breakdown of only 6 grams of body protein. However at no time does protein breakdown decrease to zero, as there is always a small requirement for glucose.
The implication of the adaptations discussed above is that the body does not require dietary carbohydrates for survival [...]. That is, there is no such thing as an essential dietary carbohydrate as the body can produce what little glucose it needs from other sources.
Of course, the price paid is the loss of body protein, which will ultimately cause death if continued for long periods of time. This loss of body protein during total starvation is unacceptable but the above discussion only serves to show that the body goes through a series of adaptations to conserve its protein. [...] the addition of dietary protein will maintain ketosis, while preventing the breakdown of bodily protein. In brief, rather than break down bodily protein to produce glucose, the body will use some of the incoming dietary protein for glucose production. This should allow maximal fat utilization while sparing protein losses.
Although the exact mechanisms behind the ‘protein sparing’ effect of ketosis are not entirely established, there are at least four possible mechanisms by which ketogenic diets may spare protein. These include decreased glucose requirements, decreased excretion of ketones from the kidneys, a possible direct effect of ketones on protein synthesis, and the drop in thyroid levels seen during starvation.
Dietary protein requirements
[...] too much protein can prevent ketosis as well, disrupting the adaptations which ketogenic dieters seek. Therefore, protein intake must fall within a narrow range: high enough to prevent muscle loss but low enough that ketosis is not disrupted.
After much research, it was concluded that a protein intake of 1.5-1.75 grams protein per kilogram of ideal body weight would spare most of the nitrogen loss, especially as ketosis developed and the body’s glucose requirements decreased.
Assuming zero carbohydrate intake, during the first 3 weeks of a ketogenic diet a protein intake of ~150 grams per day should be sufficient to achieve nitrogen balance. Therefore, regardless of bodyweight, the minimum amount of protein which should be consumed during the initial three weeks of a ketogenic diet is 150 grams per day. After 3 weeks of ketosis, as little as 50 grams of protein per day should provide enough glucose to achieve nitrogen balance.
The consumption of carbohydrate will decrease dietary protein requirements since less glucose will need to be made from protein breakdown. For example, if a person was consuming 125 grams of protein per day, this would produce 72 grams of glucose plus 18 more from the breakdown of glycerol for a total of 90 grams of glucose. To avoid any nitrogen losses, this individual could either consume 10 grams of carbohydrate per day or simply increase protein intake to 150 grams per day. (For every gram of carbohydrate consumed on a ketogenic diet, protein requirements should go down by 2 grams).
Effect of macronutrients on ketosis
The three macronutrients are carbohydrate, protein and fat. All three nutrients have differing effects on ketosis due to their digestion and subsequent effects on blood glucose and hormone levels. Carbohydrate is 100% anti-ketogenic due to its effects on blood glucose and insulin (raising both). Protein is approximately 46% ketogenic and 58% anti-ketogenic due to the fact that over half of ingested protein is converted to glucose, raising insulin. Fat is 90% ketogenic and ten percent anti-ketogenic, representing the small conversion of the glycerol portion of triglycerides to glucose. While alcohol has no direct effect on the establishment of ketosis, excessive alcohol intake can cause ketoacidosis to occur.
Water loss
A well established fact is that low-carbohydrate diets tend to cause a rapid loss of water in the first few days. This occurs [because] glycogen is stored along with water in a ratio of three grams of water for every gram of stored carbohydrate. As glycogen is depleted, water is lost. For large individuals, this can represent a lot of weight. Additionally, ketones appear to have a diuretic effect themselves causing the excretion of water and electrolytes.
The fact that the initial weight loss on a ketogenic diet is from a loss of water weight has led to a popular belief that the only weight lost on a ketogenic diet is from water, an attitude that makes little sense. The question then is whether more or less true weight is lost on a ketogenic diet versus a non-ketogenic diet.
In most studies, a low-carbohydrate diet will show a greater total weight loss than a high carbohydrate, but this is not always the case. Once water loss has been taken into account, the rate of weight loss seen, as well as the total weight loss is generally the same for ketogenic versus non-ketogenic diets. That is, if individuals are put on a 1200 calorie per day diet, they will lose roughly the same amount of ‘true’ weight (not including water) regardless of the composition of the diet.
Is a calorie deficit necessary?
A popular belief states that fat can be lost on a ketogenic diet without the creation of a caloric deficit. This implies that there is an inherent ‘calorie deficit’, or some sort of metabolic enhancement from the state of ketosis that causes fat to be lost without restriction of calories.
There are several mechanisms that might create such an inherent caloric deficit. The loss of ketones in the urine and breath represents one mechanism by which calories are wasted. However, even maximal excretion of ketones only amounts to 100 calories per day. This would amount to slightly less than one pound of extra fat lost per month.
Additionally since ketones have fewer calories per gram (4.5 cal/gram) compared to free fatty acids (9 cal/gram), it has been suggested that more fat is used to provide the same energy to the body. To provide 45 calories to the body would require 10 grams of ketones, requiring the breakdown of 10 grams of free fatty acids in the liver, versus only 5 grams of free fatty acids if they are used directly. Therefore an additional 5 grams of FFA would be ‘wasted’ to generate ketones.
However, this wastage would only occur during the first few weeks of a ketogenic diet when tissues other than the brain are deriving a large portion of their energy from ketones. After this point, the only tissue which derives a significant amount of energy from ketones is the brain. Since ketones at 4.5 calories/gram are replacing glucose at 4 calories/gram, it is hard to see how this would result in a substantially greater fat loss. Anecdotally, many individuals do report that the greatest fat loss on a ketogenic diet occurs during the first few weeks of the diet, but this pattern is not found in research.
Strangely, some individuals have reported that they can over consume calories on a ketogenic diet without gaining as much fat as would be expected. While this seems to contradict basic thermodynamics, it may be that the excess dietary fat is excreted as excess ketones rather than being stored. Frequently these individuals note that urinary ketone levels as measured by Ketostix (tm) are much deeper when they over consume calories. Obviously at some point a threshold is reached where fat consumption is higher than utilization, and fat will be stored.
One study has examined the effect of increasing amounts of dietary fat while on a low carbohydrate diet and found that up to 600 grams of fat per day could be consumed before weight gain began to occur. This effect only occurred in subjects given corn oil, which is high in essential fatty acids, but did not occur in subjects given olive oil, which is not. The corn oil subjects reported a feeling of warmth, suggesting increased caloric expenditure which generated heat. This obviously deserves further research.
One of the prime selling points of many low-carbohydrate diets is a dieter can lose weight while ‘eating as much protein and fat as they like’. While this is loosely true, this was misinterpreted by dieters and physicians alike to claim that dieters would lose weight eating unlimited amounts of foods. This idea was criticized by the American Medical Association (AMA) as it seemed to suggest that a ketogenic diet could somehow break basic laws of thermodynamics. The AMA was correct that it is impossible for dieters to lose weight while consuming unlimited calories.
However, looking at the research on ketogenic diets, we see that most individuals will automatically reduce their caloric intake when they restrict carbohydrate to low levels. Therefore, in a sense individuals are losing weight eating ‘as much as they like’, it is simply that they are eating less than they think. Studies of ketogenic diets have found that, when subjects are told to limit carbohydrate intake but to consume ‘unlimited’ quantities of protein and fat, they automatically limit caloric intake and consume between 1400-2100 calories. Any diet which automatically reduces caloric intake without inducing hunger is going to be attractive to dieters.
What about dietary fat?
With the exception of the small requirement for the EFAs, there is no essential reason to consume dietary fat as ketosis can readily be induced with a diet of all protein and a small amount of carbohydrate. However, to avoid metabolic slowdown from an excessively low caloric intake, dietary fat is necessary as a caloric ballast since protein and carbohydrates must be kept relatively static on a ketogenic diet. From a purely practical standpoint, dietary fat provides fullness and taste as a diet of pure protein is monotonously bland.
Breaking fat loss plateaus
1. Improve the nutrient quality of the low carb week
The nature of the ketogenic diet is such that most individuals tend to consume a lot of saturated fats while on the diet. Substituting some of the saturated fat intake inherent to the ketogenic diet with unsaturated fats such as fish oils and vegetable oils, may increase thermogenesis (the burning of calories to produce heat) and increase fat loss. Many individuals report a significant amount of bodily warmth following a meal high in unsaturated fats, probably due to increased thermogenesis.
2. Eat the day’s calories across fewer meals
Although this strategy is purely conjectural, some people have reported better fat loss by eating the same daily calories across fewer meals. In theory, this could allow greater fat loss as the body may be required to draw more energy from body fat stores in between meals.
3. Take a week off the diet
Although this goes against everything most dieters have been conditioned to believe, sometimes the best strategy to break a fat loss plateau is to take a week off of the diet and eat at maintenance calories. Some individuals choose to remain ketogenic, simply increasing their caloric intake, while others prefer to return to a carbohydrate based diet. The body ultimately adapts to anything including diet and calorie levels. Taking a week off of the diet can help raise metabolic rate as well as rebuild any muscle which may have been lost. However, fat gain during a one week break is generally minimal as long as individuals do not overdo caloric intake.
4. Cycle calories throughout the week
Many individuals have found success by cycling caloric intake while on a ketogenic diet. If we use a rough guideline of 12 cal/lb as an average caloric intake during the low carb week, an individual might alternate a day at slightly lower calorie levels (for example one day at 11 calories/pound) with days at slightly higher calorie levels (14 calories per pound) to get fat loss going again. Under these conditions, individuals can cautiously take calories below the 11-12 calorie/pound limit set in chapter 3 but only for a day or two at a time after which calories should be raised above 12 calories per pound. Although calorie cycling can restart fat loss, dieters must watch for signs of muscle loss. An example 7-day span where calories are cycled appears below.
Monday: 12 cal/lb
Tuesday: 10 cal/lb
Wednesday: 15 cal/lb
Thursday: 13 cal/lb
Friday: 12 cal/lb
Average caloric intake: 12.4 cal/lb
Note that the highest daily caloric intake (15 cal/lb) occurs immediately after the lowest daily caloric intake (10 cal/lb). In theory, this might help to prevent any metabolic slowdown from the low calorie day.
Scales and weighing yourself
The main problem with the scale is that it does not differentiate between what is being gained or lost (i.e. muscle, fat, water). Recall that glycogen depletion on a ketogenic diet results in a drop in body water causing immediate weight loss (5-10 lbs depending on bodyweight). Carbohydrate consumption following a period of carbohydrate restriction causes a similar increase in body weight. Individuals who tend to fixate on short-term weight changes will become frustrated by the changes in scale weight on a ketogenic diet.
Ideally the scale should always be used along with skinfold measurements or the tape measure for more accurate measures of changes in body composition. Even when body weight is stable, if body fat percentage or tape measure readings are decreasing, a loss of body fat has occurred. For best results, scale measurements should be taken first thing in the morning after going to the bathroom but before food is eaten. This will give the greatest consistency.
Please note that very few individuals will make constant linear changes in body weight and plateaus are frequent. Women will frequently gain or lose water weight during different phases of their menstrual cycle. For these reasons, regular weighing is NOT recommended for most individuals. While weekly weighing may give some indication of changes, weighing every two to four weeks may give a better indication of long term changes.
What’s the deal with Ketostix?
Whether correct or not, many ketogenic dieters tend to live or die by the presence of ketones in their urine. The presence of ketosis, which is indicative of lipolysis can be psychologically reassuring [...]. However it should be noted that one can be in ketosis, defined as ketones in the bloodstream, without showing urinary ketones.
Although up to 100 grams of carbohydrate will allow ketosis to develop, it would be rare to see ketones excreted in the urine at this level of intake. Since the only measure of ketosis available to ketogenic diets are Ketostix (tm) carbohydrates must be restricted below this level of ketosis is to be measured. As a general rule of thumb, dietary carbohydrates should be below 30 grams per day for ketosis to be rapidly established and for ketones to be lost in the urine. However, this value varies from person to person and depends on other factors such as protein intake and activity, which allows individuals to consume relatively more carbohydrate without disrupting ketosis.
After adaptation to the diet, it appears that individuals can tolerate relatively greater carbohydrate intakes without disrupting ketosis. Although not completely accurate, Ketostix (tm) can provide a rough measure of how many carbohydrates can be consumed while still maintaining ketosis. As long as trace ketosis is maintained, carbohydrates can be gradually added to the diet.
Since Ketostix (tm) only register relative concentrations, rather than absolute amounts, changes in hydration state can affect the concentration of ketones which appear. A high water intake tends to dilute urinary ketone concentrations giving lighter readings. Ketones in the urine simply indicate an overproduction of ketones such that excess spill into the urine. So it is conceivable for someone to be in ketosis without showing urinary ketones.
Some individuals can never get past trace ketosis, while others always seem to show darker readings. There seems to be little rhyme or reason as to why some individuals will always show deep concentrations of urinary ketones while others will not. Some will show higher urinary ketones after a high fat meal, suggesting that dietary fat is being converted to ketones which are then excreted. Consuming medium chain triglycerides (MCT’s) has the same effect. Other individuals seem to only register ketones on the stick after extensive aerobic exercise. Finally, there appear to be daily changes in ketone concentrations, caused by fluctuations in hormone levels. Generally ketone concentrations are smaller in the morning and larger in the evening, reaching a peak at midnight. Many individuals report high ketones at night but show no urinary ketones the next morning while others report the opposite.
A popular idea is that the deeper the level of ketosis as measured by Ketostix (tm), the greater the weight/fat loss. However there is no data to support or refute this claim. While some popular diet authors have commented that urinary ketone excretion means that bodyfat is being excreted causing fat loss, this is only loosely true in that ketones are made from the breakdown of fat in the liver. The number of calories lost in the urine as ketones amounts to 100 calories per day at most.
Anecdotally, higher levels of urinary ketones seem to be indicative of slower fat loss. Individuals who maintain trace ketosis seem to lose fat more efficiently although there is no research examining this phenomenon. A possible reason is this: high levels of ketones in the bloodstream raise insulin slightly and block the release of free fatty acids from fat cells. This seems to imply that higher levels of ketones will slow fat mobilization.
The ideal situation would seem to be one where trace ketosis (as measured by Ketostix(tm)) is maintained, since this is the lowest level of ketosis which can be measured while still ensuring that one is truly in ketosis. This should be indicative of relatively lower blood ketone concentrations, meaning that bodyfat can be mobilized more efficiently.
No hard and fast rules can be given for the use of Ketostix (tm) except not to be obsessive about them. In the same way that the presence of ketones can be psychologically reassuring, the absence of ketones can be just as psychologically harmful. It is easy to mentally shortcircuit by checking the Ketostix (tm) all the time.
Exercise & Ketosis
When muscle glycogen falls to extremely low levels (about 40 mmol/kg), anaerobic exercise performance may be negatively affected. Individuals following a ketogenic diet who wish to lift weights or perform sprint training must make modifications by consuming carbohydrates for optimal performance. During long term ketogenic diets, muscle glycogen maintains at about 70 mmol/kg (113-115) leaving a ‘safety factor’ of about 30 mmol/kg at which time glycolysis will most likely be impaired.
Low-intensity aerobic exercise, below the lactate threshold, is useful for both establishing ketosis following an overnight fast as well as deepening ketosis. High-intensity exercise will more quickly establish ketosis by forcing the liver to release glycogen into the bloodstream. However it can decrease the depth of ketosis by decreasing the availability of FFA. Performing ten minutes or more of low-intensity aerobics following high-intensity activity will help re-establish ketosis after high-intensity activity.
There is a caloric threshold for exercise to improve the rate of fat loss. A calorie deficit more than 1000 cal/day will slow metabolism. Further increases in energy expenditure past that level does not increase fat loss. In some cases, excess exercise will increase the drop in metabolic rate seen with very large calorie deficits. This value of 1000 calories per day includes any caloric deficit AND exercise. Meaning that if 500 calories per day are removed from the diet, no more than 500 calories per day of exercise should be performed. If someone chose to remove 1000 calories per day from their diet, no aerobic exercise should be done to avoid metabolic slowdown.
The decrease in metabolic rate seen with very low-calorie diets makes weight regain likely. Eventually, a dieter will have to eat. And when normal eating habits are resumed after a period of starvation dieting, weight and bodyfat regain will be the result. Therefore the best fat loss solution, in terms of both fat loss as well as maintenance of that fat loss, is to eat at maintenance (or a slight deficit, no more than 10-20% below maintenance) in combination with resistance training. Aerobic training can be added as required and will increase fat loss as long as it is not overdone. For most, 20-40 minutes of aerobic exercise several times per week should be sufficient. In this case, more is NOT better. However, if an individual has significant amounts of fat to lose, a greater frequency of aerobic exercise may be beneficial.
The ultimate point of the above discussion is this: resistance training coupled with a slight decrease in energy balance is the key to fat loss. The inclusion of aerobic training can increase fat loss as long as total calories are not taken too low
Supplements
Any calorically restricted diet may not provide for all nutritional requirements and the limited number of food available on a ketogenic diet may cause deficiencies [...]. At the very least, individuals on a ketogenic diet should take some form of sugar free vitamin and mineral supplement to ensure nutritional adequacy. Additionally, supplemental sodium, magnesium and potassium may be necessary [...]. Depending on dairy intake, a calcium supplement may also be necessary.
A great deal of recent research is currently focusing on the benefit of various anti-oxidant nutrients such as vitamin C, vitamin E and beta-carotene. These substances, as well as many others, may help to prevent tissue damage from substances called ‘free radicals’. Free radicals are thought to damage cells causing the accumulation of toxic chemicals. Individuals involved in intense exercise appear to generate an excess of free radicals so supplementation may be indicated. Additionally, the few carbohydrates which are consumed on a ketogenic diet should come from a variety of vegetable sources whenever possible.
[...] a common side effect of ketogenic diets is a decrease in bowel movements. At least part of this is caused by the general lack of fiber in the ketogenic diet. For this reason, a sugar-free fiber supplement may be useful to maintain regularity. Additionally, the inclusion of high fiber vegetables, such as a large salad, can help with regularity in addition to the nutrients they provide.
Other suggested supplements: Essential fatty acids (EFAs), Omega-3 and omega-6 fatty acids and Olive oil
~ summary by L6S
...for more information, visit www.bodyrecomposition.com
By: Lyle McDonald
What is a ketogenic diet?
In the most general terms, a ketogenic diet is any diet that causes ketone bodies to be produced by the liver, shifting the body’s metabolism away from glucose and towards fat utilization. More specifically, a ketogenic diet is one that restricts carbohydrates below a certain level (generally 100 grams per day), inducing a series of adaptations to take place.
Basics of fuel utilization
There are four primary fuels which can be used in the human body: glucose, protein, free fatty acids, and ketones. [...] the primary form of stored fuel is triglyceride, stored in adipose tissue. Glucose and protein make up secondary sources. These fuels are used in varying proportions depending on the metabolic state of the body.
The primary determinant of fuel utilization in humans is carbohydrate availability, which affects hormone levels. Additional factors affecting fuel utilization are the status of liver glycogen (full or empty) as well as the levels of certain enzymes.
When present in sufficient quantities, glucose is the preferred fuel for most tissues in the body. The major exception to this is the heart, which uses a mix of glucose, FFA and ketones.
The major source of glucose in the body is from dietary carbohydrate. However, other substances can be converted to glucose in the liver and kidney through a process called gluconeogenesis. If glucose requirements are high but glucose availability is low, [...] the body will break down its own protein stores to produce glucose. [...] an adequate protein intake during the first weeks of a ketogenic diet will prevent muscle loss by supplying the amino acids for gluconeogenesis that would otherwise come from body proteins.
Most tissues of the body can use FFA for fuel if it is available. This includes skeletal muscle, the heart, and most organs. However, there are other tissues such as the brain, red blood cells, the renal medulla, bone marrow and Type II muscle fibers which cannot use FFA and require glucose.
The Brain
The fact that the brain is incapable of using FFA for fuel has led to one of the biggest misconceptions about human physiology: that the brain can only use glucose for fuel. While it is true that the brain normally runs on glucose, the brain will readily use ketones for fuel if they are available.
In a non-ketotic state, the brain utilizes roughly 100 grams of glucose per day. This means that any diet which contains less than 100 grams of carbohydrate per day will induce ketosis, the depth of which will depend on how many carbohydrates are consumed (i.e. less carbohydrates will mean deeper ketosis). During the initial stages of ketosis, any carbohydrate intake below 100 grams will induce ketosis. As the brain adapts to using ketones for fuel and the body’s glucose requirements decrease, less carbohydrate must be consumed if ketosis is to be maintained.
[...] the brain which can derive up to 75% of its total energy requirements from ketones after adaptation. In all likelihood, ketones exist primarily to provide a fat-derived fuel for the brain during periods when carbohydrates are unavailable.
Utilization of ketones in the body
Under normal dietary conditions, ketone concentrations are so low that ketones provide a negligible amount of energy to the tissues of the body. If ketone concentrations increase, most tissues in the body will begin to derive some portion of their energy requirements from ketones. Some research also suggests that ketones are the preferred fuel of many tissues. One exception is the liver which does not use ketones for fuel, relying instead on FFA.
By the third day of ketosis, all of the non-protein fuel is derived from the oxidation of FFA and ketones. As ketosis develops, most tissues which can use ketones for fuel will stop using them to a significant degree by the third week. This decrease in ketone utilization occurs due to a down regulation of the enzymes responsible for ketone use and occurs in all tissues except the brain. After three weeks, most tissues will meet their energy requirements almost exclusively through the breakdown of FFA. This is thought to be an adaptation to ensure adequate ketone levels for the brain.
Storing fuel
Excess dietary carbohydrates can be converted to fat in the liver through a process called de novo lipognesis (DNL). However short term studies show that DNL does not contribute significantly to fat gain in humans. As long as muscle and liver glycogen stores are not completely filled, the body is able to store or burn off excess dietary carbohydrates. Of course this process occurs at the expense of limiting fat burning, meaning that any dietary fat which is ingested with a high carbohydrate intake is stored as fat.
The most likely scenario in which this would occur would be one in which an individual was inactive and consuming an excess of carbohydrates/calories in their diet. As well, the combination of inactivity with a very high carbohydrate AND high fat diet is much worse in terms of fat gain. With chronically over-filled glycogen stores and a high carbohydrate intake, fat utilization is almost completely blocked and any dietary fat consumed is stored. This has led some authors to suggest an absolute minimization of dietary fat for weight loss. The premise is that, since incoming carbohydrate will block fat burning by the body, less fat must be eaten to avoid storage. The ketogenic diet approaches this problem from the opposite direction. By reducing carbohydrate intake to minimum levels, fat utilization by the body is maximized.
A high carbohydrate diet decreases the use of fat for fuel and vice versa. Thus, the greatest rates of fat oxidation will occur under conditions when carbohydrates are restricted. As well, the level of muscle glycogen regulates how much fat is used by the muscle [...]. Using exercise and/or carbohydrate restriction to lower muscle and liver glycogen levels increases fat utilization.
Summary: When carbohydrate availability is high, carbohydrate use and storage is high and fat use is low. When carbohydrate availability is low, carbohydrate use and storage is low and fat use is high. The most basic premise of the ketogenic diet is that the body can be forced to burn greater amounts of fat by decreasing its use of glucose.
Insulin
Insulin is a peptide (protein based) hormone released from the pancreas, primarily in response to increases in blood glucose. When blood glucose increases, insulin levels increase as well, causing glucose in the bloodstream to be stored as glycogen in the muscle or liver. Excess glucose can be pushed into fat cells for storage (as alpha-glycerophosphate). Protein synthesis is stimulated and free amino acids (the building blocks of proteins) are moved into muscle cells and incorporated into larger proteins. Fat synthesis (called lipogenesis) and fat storage are both stimulated. FFA release from fat cells is inhibited by even small amounts of insulin.
The primary role of insulin is to keep blood glucose in the fairly narrow range of roughly 80-120 mg/dl. When blood glucose increases outside of this range, insulin is released to lower blood glucose back to normal. The greatest increase in blood glucose levels (and the greatest increase in insulin) occurs from the consumption of dietary carbohydrates. Protein causes a smaller increase in insulin output because some individual amino acids can be converted to glucose. FFA can stimulate insulin release as can high concentrations of ketone bodies although to a much lesser degree than carbohydrate or protein.
Basic ketone physiology
The three ketone bodies are acetoacetate (AcAc), beta-hydroxybutyrate (BHB) and acetone. AcAc and BHB are produced from the condensation of acetyl-CoA, a product of incomplete breakdown of free fatty acids (FFA) in the liver. While ketones can technically be made from certain amino acids, this is not thought to contribute significantly to ketosis. Roughly one-third of AcAc is converted to acetone, which is excreted in the breath and urine. This gives some individuals on a ketogenic diet a ‘fruity’ smelling breath.
As a side note, urinary and breath excretion of acetone is negligible in terms of caloric loss, amounting to a maximum of 100 calories per day. The fact that ketones are excreted through this pathway has led some authors to argue that fat loss is being accomplished through urination and breathing. While this may be very loosely true, in that ketones are produced from the breakdown of fat and energy is being lost through these routes, the number of calories lost per day will have a minimal effect on fat loss.
While many tissues of the body (especially muscle) use a large amount of ketones for fuel during the first few weeks of a ketogenic diet, most of these same tissues will decrease their use of ketones as the length of time in ketosis increases. At this time, these tissues rely primarily on the breakdown of free fatty acids (FFA). In practical terms, after three weeks of a ketogenic diet, the use of ketones by tissues other than the brain is negligible and can be ignored.
The liver is always producing ketones to some small degree and they are always present in the bloodstream. Under normal dietary conditions, ketone concentrations are simply too low to be of any physiological consequence. A ketogenic diet increases the amount of ketones which are produced and the blood concentrations seen. Thus ketones should not be considered a toxic substance or a byproduct of abnormal human metabolism. Rather, ketones are a normal physiological substance that plays many important roles in the human body.
Ketosis vs. Ketoacidosis
Ketosis occurs in a number of physiological states including fasting (called starvation ketosis), the consumption of a high fat diet (called dietary ketosis), and immediately after exercise (called post-exercise ketosis). Two pathological and potentially fatal metabolic states during which ketosis occurs are diabetic ketoacidosis and alcoholic ketoacidosis.
The major difference between starvation, dietary and diabetic/alcoholic ketoacidosis is in the level of ketone concentrations seen in the blood. Starvation and dietary ketosis will normally not progress to dangerous levels, due to various feedback loops which are present in the body. Diabetic and alcoholic ketoacidosis are both potentially fatal conditions.
Under normal conditions, ketone bodies are present in the bloodstream in minute amounts, approximately 0.1 mmol/dl. When ketone body formation increases in the liver, ketones begin to accumulate in the bloodstream. Ketosis is defined clinically as a ketone concentration above 0.2 mmol/dl. Mild ketosis, around 2 mmol, also occurs following aerobic exercise. Ketoacidosis is defined as any ketone concentration above 7 mmol/dl. Diabetic and alcoholic ketoacidosis result in ketone concentrations up to 25 mmol. This level of ketosis will never occur in non-diabetic or alcoholic individuals.
Additionally, in non-diabetic individuals there are at least two feedback loops to prevent runaway ketoacidosis from occurring. When ketones reach high concentrations in the bloodstream (approximately 4-6 mmol), they stimulate a release of insulin. This increase in insulin has three major effects. First, it slows FFA release from the fat cell. Second, by raising the insulin/glucagon ratio, the rate of ketone body formation in the liver is decreased. Third, it increases the excretion of ketones into the urine. These three effects all serve to lower blood ketone body concentration.
In addition to stimulating insulin release, ketones appear to have an impact directly on the fat cell, slowing FFA release. This would serve to limit FFA availability to the liver, slowing ketone body formation. Ultimately these two feedback loops prevent the non-diabetic individual from over producing ketones since high ketone levels decrease ketone body formation.
Ketonemia vs. Ketonuria
The general metabolic state of ketosis can be further subdivided into two categories. The first is ketonemia which describes the buildup of ketone bodies in the bloodstream. Technically ketonemia is the true indicator that ketosis has been induced. However the only way to measure the level of ketonemia is with a blood test which is not practical for ketogenic dieters.
The second subdivision is ketonuria which describes the buildup and excretion of ketone bodies in the urine, which occurs due to the accumulation of ketones in the kidney. The excretion of ketones into the urine may represent 10-20% of the total ketones made in the liver. However, this may only amount to 10-20 grams of total ketones excreted per day. Since ketones have a caloric value of 4.5 calories/gram, the loss of calories through the urine is only 45-90 calories per day. The degree of ketonuria, which is an indirect indicator of ketonemia, can be measured by the use of Ketostix (tm), small paper strips which react with urinary ketones and change color.
Ketonemia will always occur before ketonuria. Ketone concentrations tend to vary throughout the day and are generally lower in the morning, reaching a peak around midnight. This may occur from changes in hormone levels throughout the day. Additionally, women appear to show deeper ketone levels than men and children develop deeper ketosis than do adults. Finally, certain supplements, such as N-acetyl-cysteine, a popular anti-oxidant, can falsely indicate ketosis.
The distinction between ketonuria and ketonemia is important from a practical standpoint. Some individuals, who have followed all of the guidelines for establishing ketosis will not show urinary ketones. However this does not mean that they are not technically in ketosis. Ketonuria is only an indirect measure of ketone concentrations in the bloodstream and Ketostix (tm) measurements can be inaccurate.
Adaptations to Ketosis
In one sense, the ketogenic diet is identical to starvation, except that food is being consumed. That is, the metabolic effects which occur and the adaptations which are seen during starvation are roughly identical to what is seen during a ketogenic diet. The primary difference is that the protein and fat intake of a ketogenic diet will replace some of the protein and fat which would otherwise be used for fuel during starvation.
During the first 3 days of fasting, blood glucose drops from normal levels of 80-120 mg/dl to roughly 65-75 mg/dl. Insulin drops from 40-50 µU/ml to 7-10 µU/ml. Both remain constant for the duration of the fast. One thing to note is that the body strives to maintain near normal blood glucose levels even under conditions of total fasting. The popularly held belief that ketosis will not occur until blood glucose falls to 50 mg/dl is incorrect.
Additionally, the popular belief that there is no insulin present on a ketogenic diet is incorrect. One difference between fasting and a ketogenic diet is that the slight insulin response to dietary protein will cause blood glucose to be maintained at a slightly higher level, approximately 80-85 mg/dl. This most likely occurs due to the conversion of dietary protein to glucose in the liver.
Although the liver is producing ketones at its maximum rate by day three, blood ketone levels will continue to increase finally reaching a plateau by three weeks. The decrease in blood glucose and subsequent increase in FFA and ketones appear to be the signal for the adaptations which are seen [...]. Measurements of fuel use show that approximately 90% of the body’s total fuel requirements are being met by FFA and ketones by the third day. After three weeks of starvation, the body may derive 93% of its fuel from FFA.
Most tissues except the brain, stop using ketones for fuel after the third week of ketosis. This is especially true for skeletal muscle. While muscle initially derives up to 50% of its energy requirements from ketones, this drops to 4-6% by the third week of ketosis.
Why do the use of ketones drop?
During the first few days of ketosis, the brain is incapable of using ketones for fuel. By using a large amount of ketones for fuel, skeletal muscle prevents a rapid increase in blood ketone levels, which might cause acidosis. As time passes and the brain adapts to using ketones for fuel, skeletal muscle must stop using ketones for fuel, to avoid depriving the brain of fuel. For all practical purposes, with long term starvation, the primary fuel of all tissues except the brain is FFA, not ketones.
All tissues in the body have the capacity to use glucose. With the exception of the brain and a few other tissues (leukocytes, bone marrow, erythrocytes), all tissues in the body can use FFA or ketones for fuel when carbohydrate is not available.
Under normal dietary conditions, glucose is the standard fuel for the brain and central nervous system (CNS). The CNS and brain are the largest consumers of glucose on a daily basis, requiring roughly 104 grams of glucose per day. This peculiarity of brain metabolism has led to probably the most important misconception regarding the ketogenic diet. A commonly heard statement is that the brain can only use glucose for fuel but this is only conditionally true. It has been known for over 30 years that, once ketosis has been established for a few days, the brain will derive more and more of its fuel requirements from ketones, finally deriving over half of its energy needs from ketones with the remainder coming from glucose.
As a few tissues do continue to use glucose for fuel, and since the brain’s glucose requirement never drops to zero, there will still be a small glucose requirement on a ketogenic diet. This raises the question of how much glucose is required by the body and whether or not this amount can be provided on a diet completely devoid of carbohydrate.
Adaptations when carbs are restricted
When carbohydrate is removed from the diet, the body undergoes at least three major adaptations to conserve what little glucose and protein it does have.
The primary adaptation is an overall shift in fuel utilization from glucose to FFA in most tissues, as discussed in the previous section. This shift spares what little glucose is available to fuel the brain.
The second adaptation occurs in the leukocytes, erythrocytes and bone marrow which continue to use glucose. To prevent a depletion of available glucose stores, these tissues break down glucose partially to lactate and pyruvate which go to the liver and are recycled back to glucose again. Thus there is no net loss of glucose in the body from these tissues and they can be ignored in terms of the body’s carbohydrate requirements.
The third, and probably the most important, adaptation, occurs in the brain, which shifts from using solely carbohydrate for fuel to deriving up to 75% of its energy requirements from ketones by the third week of sustained ketosis. As the brain is the only tissue that continues to deplete glucose in the body, it is all we need concern ourselves with in terms of daily carbohydrate requirements.
Glycogen
The initial storage depot of carbohydrate in the body is the liver, which contains enough glycogen to sustain the brain’s glucose needs for approximately 12-16 hours. We will assume for the following discussion that liver glycogen has been depleted, ketosis established, and that the only source of glucose is from endogenous fuel stores (i.e. stored bodyfat and protein). After its glycogen has been depleted, the liver is one of the major sources for the production of glucose (gluconeogenesis) and it produces glucose from glycerol, lactate/pyruvate and the amino acids alanine and glutamine. The kidney also produces glucose as starvation proceeds.
Protein and muscle loss
During the initial weeks of starvation, there is an excretion of 12 grams of nitrogen per day. Since approximately 16% of protein is nitrogen, this represents the breakdown of roughly 75 grams of body protein to produce 75 grams of glucose. If this rate of protein breakdown were to continue unchecked, the body’s protein stores would be depleted in a matter of weeks, causing death.
After even 1 week of starvation, blood alanine levels begin to drop and uptake by the kidneys decreases, indicating that the body is already trying to spare protein losses. During longer periods of starvation, blood levels of alanine and glutamine continue to decrease, as does glucose production by the liver. As glucose production in the liver is decreasing, there is increased glucose production in the kidney.
Because of these adaptations, nitrogen losses decrease to 3-4 grams per day by the third week of starvation, indicating the breakdown of approximately 20 grams of body protein. With extremely long term starvation, nitrogen losses may drop to 1 gram per day, indicating the breakdown of only 6 grams of body protein. However at no time does protein breakdown decrease to zero, as there is always a small requirement for glucose.
The implication of the adaptations discussed above is that the body does not require dietary carbohydrates for survival [...]. That is, there is no such thing as an essential dietary carbohydrate as the body can produce what little glucose it needs from other sources.
Of course, the price paid is the loss of body protein, which will ultimately cause death if continued for long periods of time. This loss of body protein during total starvation is unacceptable but the above discussion only serves to show that the body goes through a series of adaptations to conserve its protein. [...] the addition of dietary protein will maintain ketosis, while preventing the breakdown of bodily protein. In brief, rather than break down bodily protein to produce glucose, the body will use some of the incoming dietary protein for glucose production. This should allow maximal fat utilization while sparing protein losses.
Although the exact mechanisms behind the ‘protein sparing’ effect of ketosis are not entirely established, there are at least four possible mechanisms by which ketogenic diets may spare protein. These include decreased glucose requirements, decreased excretion of ketones from the kidneys, a possible direct effect of ketones on protein synthesis, and the drop in thyroid levels seen during starvation.
Dietary protein requirements
[...] too much protein can prevent ketosis as well, disrupting the adaptations which ketogenic dieters seek. Therefore, protein intake must fall within a narrow range: high enough to prevent muscle loss but low enough that ketosis is not disrupted.
After much research, it was concluded that a protein intake of 1.5-1.75 grams protein per kilogram of ideal body weight would spare most of the nitrogen loss, especially as ketosis developed and the body’s glucose requirements decreased.
Assuming zero carbohydrate intake, during the first 3 weeks of a ketogenic diet a protein intake of ~150 grams per day should be sufficient to achieve nitrogen balance. Therefore, regardless of bodyweight, the minimum amount of protein which should be consumed during the initial three weeks of a ketogenic diet is 150 grams per day. After 3 weeks of ketosis, as little as 50 grams of protein per day should provide enough glucose to achieve nitrogen balance.
The consumption of carbohydrate will decrease dietary protein requirements since less glucose will need to be made from protein breakdown. For example, if a person was consuming 125 grams of protein per day, this would produce 72 grams of glucose plus 18 more from the breakdown of glycerol for a total of 90 grams of glucose. To avoid any nitrogen losses, this individual could either consume 10 grams of carbohydrate per day or simply increase protein intake to 150 grams per day. (For every gram of carbohydrate consumed on a ketogenic diet, protein requirements should go down by 2 grams).
Effect of macronutrients on ketosis
The three macronutrients are carbohydrate, protein and fat. All three nutrients have differing effects on ketosis due to their digestion and subsequent effects on blood glucose and hormone levels. Carbohydrate is 100% anti-ketogenic due to its effects on blood glucose and insulin (raising both). Protein is approximately 46% ketogenic and 58% anti-ketogenic due to the fact that over half of ingested protein is converted to glucose, raising insulin. Fat is 90% ketogenic and ten percent anti-ketogenic, representing the small conversion of the glycerol portion of triglycerides to glucose. While alcohol has no direct effect on the establishment of ketosis, excessive alcohol intake can cause ketoacidosis to occur.
Water loss
A well established fact is that low-carbohydrate diets tend to cause a rapid loss of water in the first few days. This occurs [because] glycogen is stored along with water in a ratio of three grams of water for every gram of stored carbohydrate. As glycogen is depleted, water is lost. For large individuals, this can represent a lot of weight. Additionally, ketones appear to have a diuretic effect themselves causing the excretion of water and electrolytes.
The fact that the initial weight loss on a ketogenic diet is from a loss of water weight has led to a popular belief that the only weight lost on a ketogenic diet is from water, an attitude that makes little sense. The question then is whether more or less true weight is lost on a ketogenic diet versus a non-ketogenic diet.
In most studies, a low-carbohydrate diet will show a greater total weight loss than a high carbohydrate, but this is not always the case. Once water loss has been taken into account, the rate of weight loss seen, as well as the total weight loss is generally the same for ketogenic versus non-ketogenic diets. That is, if individuals are put on a 1200 calorie per day diet, they will lose roughly the same amount of ‘true’ weight (not including water) regardless of the composition of the diet.
Is a calorie deficit necessary?
A popular belief states that fat can be lost on a ketogenic diet without the creation of a caloric deficit. This implies that there is an inherent ‘calorie deficit’, or some sort of metabolic enhancement from the state of ketosis that causes fat to be lost without restriction of calories.
There are several mechanisms that might create such an inherent caloric deficit. The loss of ketones in the urine and breath represents one mechanism by which calories are wasted. However, even maximal excretion of ketones only amounts to 100 calories per day. This would amount to slightly less than one pound of extra fat lost per month.
Additionally since ketones have fewer calories per gram (4.5 cal/gram) compared to free fatty acids (9 cal/gram), it has been suggested that more fat is used to provide the same energy to the body. To provide 45 calories to the body would require 10 grams of ketones, requiring the breakdown of 10 grams of free fatty acids in the liver, versus only 5 grams of free fatty acids if they are used directly. Therefore an additional 5 grams of FFA would be ‘wasted’ to generate ketones.
However, this wastage would only occur during the first few weeks of a ketogenic diet when tissues other than the brain are deriving a large portion of their energy from ketones. After this point, the only tissue which derives a significant amount of energy from ketones is the brain. Since ketones at 4.5 calories/gram are replacing glucose at 4 calories/gram, it is hard to see how this would result in a substantially greater fat loss. Anecdotally, many individuals do report that the greatest fat loss on a ketogenic diet occurs during the first few weeks of the diet, but this pattern is not found in research.
Strangely, some individuals have reported that they can over consume calories on a ketogenic diet without gaining as much fat as would be expected. While this seems to contradict basic thermodynamics, it may be that the excess dietary fat is excreted as excess ketones rather than being stored. Frequently these individuals note that urinary ketone levels as measured by Ketostix (tm) are much deeper when they over consume calories. Obviously at some point a threshold is reached where fat consumption is higher than utilization, and fat will be stored.
One study has examined the effect of increasing amounts of dietary fat while on a low carbohydrate diet and found that up to 600 grams of fat per day could be consumed before weight gain began to occur. This effect only occurred in subjects given corn oil, which is high in essential fatty acids, but did not occur in subjects given olive oil, which is not. The corn oil subjects reported a feeling of warmth, suggesting increased caloric expenditure which generated heat. This obviously deserves further research.
One of the prime selling points of many low-carbohydrate diets is a dieter can lose weight while ‘eating as much protein and fat as they like’. While this is loosely true, this was misinterpreted by dieters and physicians alike to claim that dieters would lose weight eating unlimited amounts of foods. This idea was criticized by the American Medical Association (AMA) as it seemed to suggest that a ketogenic diet could somehow break basic laws of thermodynamics. The AMA was correct that it is impossible for dieters to lose weight while consuming unlimited calories.
However, looking at the research on ketogenic diets, we see that most individuals will automatically reduce their caloric intake when they restrict carbohydrate to low levels. Therefore, in a sense individuals are losing weight eating ‘as much as they like’, it is simply that they are eating less than they think. Studies of ketogenic diets have found that, when subjects are told to limit carbohydrate intake but to consume ‘unlimited’ quantities of protein and fat, they automatically limit caloric intake and consume between 1400-2100 calories. Any diet which automatically reduces caloric intake without inducing hunger is going to be attractive to dieters.
What about dietary fat?
With the exception of the small requirement for the EFAs, there is no essential reason to consume dietary fat as ketosis can readily be induced with a diet of all protein and a small amount of carbohydrate. However, to avoid metabolic slowdown from an excessively low caloric intake, dietary fat is necessary as a caloric ballast since protein and carbohydrates must be kept relatively static on a ketogenic diet. From a purely practical standpoint, dietary fat provides fullness and taste as a diet of pure protein is monotonously bland.
Breaking fat loss plateaus
1. Improve the nutrient quality of the low carb week
The nature of the ketogenic diet is such that most individuals tend to consume a lot of saturated fats while on the diet. Substituting some of the saturated fat intake inherent to the ketogenic diet with unsaturated fats such as fish oils and vegetable oils, may increase thermogenesis (the burning of calories to produce heat) and increase fat loss. Many individuals report a significant amount of bodily warmth following a meal high in unsaturated fats, probably due to increased thermogenesis.
2. Eat the day’s calories across fewer meals
Although this strategy is purely conjectural, some people have reported better fat loss by eating the same daily calories across fewer meals. In theory, this could allow greater fat loss as the body may be required to draw more energy from body fat stores in between meals.
3. Take a week off the diet
Although this goes against everything most dieters have been conditioned to believe, sometimes the best strategy to break a fat loss plateau is to take a week off of the diet and eat at maintenance calories. Some individuals choose to remain ketogenic, simply increasing their caloric intake, while others prefer to return to a carbohydrate based diet. The body ultimately adapts to anything including diet and calorie levels. Taking a week off of the diet can help raise metabolic rate as well as rebuild any muscle which may have been lost. However, fat gain during a one week break is generally minimal as long as individuals do not overdo caloric intake.
4. Cycle calories throughout the week
Many individuals have found success by cycling caloric intake while on a ketogenic diet. If we use a rough guideline of 12 cal/lb as an average caloric intake during the low carb week, an individual might alternate a day at slightly lower calorie levels (for example one day at 11 calories/pound) with days at slightly higher calorie levels (14 calories per pound) to get fat loss going again. Under these conditions, individuals can cautiously take calories below the 11-12 calorie/pound limit set in chapter 3 but only for a day or two at a time after which calories should be raised above 12 calories per pound. Although calorie cycling can restart fat loss, dieters must watch for signs of muscle loss. An example 7-day span where calories are cycled appears below.
Monday: 12 cal/lb
Tuesday: 10 cal/lb
Wednesday: 15 cal/lb
Thursday: 13 cal/lb
Friday: 12 cal/lb
Average caloric intake: 12.4 cal/lb
Note that the highest daily caloric intake (15 cal/lb) occurs immediately after the lowest daily caloric intake (10 cal/lb). In theory, this might help to prevent any metabolic slowdown from the low calorie day.
Scales and weighing yourself
The main problem with the scale is that it does not differentiate between what is being gained or lost (i.e. muscle, fat, water). Recall that glycogen depletion on a ketogenic diet results in a drop in body water causing immediate weight loss (5-10 lbs depending on bodyweight). Carbohydrate consumption following a period of carbohydrate restriction causes a similar increase in body weight. Individuals who tend to fixate on short-term weight changes will become frustrated by the changes in scale weight on a ketogenic diet.
Ideally the scale should always be used along with skinfold measurements or the tape measure for more accurate measures of changes in body composition. Even when body weight is stable, if body fat percentage or tape measure readings are decreasing, a loss of body fat has occurred. For best results, scale measurements should be taken first thing in the morning after going to the bathroom but before food is eaten. This will give the greatest consistency.
Please note that very few individuals will make constant linear changes in body weight and plateaus are frequent. Women will frequently gain or lose water weight during different phases of their menstrual cycle. For these reasons, regular weighing is NOT recommended for most individuals. While weekly weighing may give some indication of changes, weighing every two to four weeks may give a better indication of long term changes.
What’s the deal with Ketostix?
Whether correct or not, many ketogenic dieters tend to live or die by the presence of ketones in their urine. The presence of ketosis, which is indicative of lipolysis can be psychologically reassuring [...]. However it should be noted that one can be in ketosis, defined as ketones in the bloodstream, without showing urinary ketones.
Although up to 100 grams of carbohydrate will allow ketosis to develop, it would be rare to see ketones excreted in the urine at this level of intake. Since the only measure of ketosis available to ketogenic diets are Ketostix (tm) carbohydrates must be restricted below this level of ketosis is to be measured. As a general rule of thumb, dietary carbohydrates should be below 30 grams per day for ketosis to be rapidly established and for ketones to be lost in the urine. However, this value varies from person to person and depends on other factors such as protein intake and activity, which allows individuals to consume relatively more carbohydrate without disrupting ketosis.
After adaptation to the diet, it appears that individuals can tolerate relatively greater carbohydrate intakes without disrupting ketosis. Although not completely accurate, Ketostix (tm) can provide a rough measure of how many carbohydrates can be consumed while still maintaining ketosis. As long as trace ketosis is maintained, carbohydrates can be gradually added to the diet.
Since Ketostix (tm) only register relative concentrations, rather than absolute amounts, changes in hydration state can affect the concentration of ketones which appear. A high water intake tends to dilute urinary ketone concentrations giving lighter readings. Ketones in the urine simply indicate an overproduction of ketones such that excess spill into the urine. So it is conceivable for someone to be in ketosis without showing urinary ketones.
Some individuals can never get past trace ketosis, while others always seem to show darker readings. There seems to be little rhyme or reason as to why some individuals will always show deep concentrations of urinary ketones while others will not. Some will show higher urinary ketones after a high fat meal, suggesting that dietary fat is being converted to ketones which are then excreted. Consuming medium chain triglycerides (MCT’s) has the same effect. Other individuals seem to only register ketones on the stick after extensive aerobic exercise. Finally, there appear to be daily changes in ketone concentrations, caused by fluctuations in hormone levels. Generally ketone concentrations are smaller in the morning and larger in the evening, reaching a peak at midnight. Many individuals report high ketones at night but show no urinary ketones the next morning while others report the opposite.
A popular idea is that the deeper the level of ketosis as measured by Ketostix (tm), the greater the weight/fat loss. However there is no data to support or refute this claim. While some popular diet authors have commented that urinary ketone excretion means that bodyfat is being excreted causing fat loss, this is only loosely true in that ketones are made from the breakdown of fat in the liver. The number of calories lost in the urine as ketones amounts to 100 calories per day at most.
Anecdotally, higher levels of urinary ketones seem to be indicative of slower fat loss. Individuals who maintain trace ketosis seem to lose fat more efficiently although there is no research examining this phenomenon. A possible reason is this: high levels of ketones in the bloodstream raise insulin slightly and block the release of free fatty acids from fat cells. This seems to imply that higher levels of ketones will slow fat mobilization.
The ideal situation would seem to be one where trace ketosis (as measured by Ketostix(tm)) is maintained, since this is the lowest level of ketosis which can be measured while still ensuring that one is truly in ketosis. This should be indicative of relatively lower blood ketone concentrations, meaning that bodyfat can be mobilized more efficiently.
No hard and fast rules can be given for the use of Ketostix (tm) except not to be obsessive about them. In the same way that the presence of ketones can be psychologically reassuring, the absence of ketones can be just as psychologically harmful. It is easy to mentally shortcircuit by checking the Ketostix (tm) all the time.
Exercise & Ketosis
When muscle glycogen falls to extremely low levels (about 40 mmol/kg), anaerobic exercise performance may be negatively affected. Individuals following a ketogenic diet who wish to lift weights or perform sprint training must make modifications by consuming carbohydrates for optimal performance. During long term ketogenic diets, muscle glycogen maintains at about 70 mmol/kg (113-115) leaving a ‘safety factor’ of about 30 mmol/kg at which time glycolysis will most likely be impaired.
Low-intensity aerobic exercise, below the lactate threshold, is useful for both establishing ketosis following an overnight fast as well as deepening ketosis. High-intensity exercise will more quickly establish ketosis by forcing the liver to release glycogen into the bloodstream. However it can decrease the depth of ketosis by decreasing the availability of FFA. Performing ten minutes or more of low-intensity aerobics following high-intensity activity will help re-establish ketosis after high-intensity activity.
There is a caloric threshold for exercise to improve the rate of fat loss. A calorie deficit more than 1000 cal/day will slow metabolism. Further increases in energy expenditure past that level does not increase fat loss. In some cases, excess exercise will increase the drop in metabolic rate seen with very large calorie deficits. This value of 1000 calories per day includes any caloric deficit AND exercise. Meaning that if 500 calories per day are removed from the diet, no more than 500 calories per day of exercise should be performed. If someone chose to remove 1000 calories per day from their diet, no aerobic exercise should be done to avoid metabolic slowdown.
The decrease in metabolic rate seen with very low-calorie diets makes weight regain likely. Eventually, a dieter will have to eat. And when normal eating habits are resumed after a period of starvation dieting, weight and bodyfat regain will be the result. Therefore the best fat loss solution, in terms of both fat loss as well as maintenance of that fat loss, is to eat at maintenance (or a slight deficit, no more than 10-20% below maintenance) in combination with resistance training. Aerobic training can be added as required and will increase fat loss as long as it is not overdone. For most, 20-40 minutes of aerobic exercise several times per week should be sufficient. In this case, more is NOT better. However, if an individual has significant amounts of fat to lose, a greater frequency of aerobic exercise may be beneficial.
The ultimate point of the above discussion is this: resistance training coupled with a slight decrease in energy balance is the key to fat loss. The inclusion of aerobic training can increase fat loss as long as total calories are not taken too low
Supplements
Any calorically restricted diet may not provide for all nutritional requirements and the limited number of food available on a ketogenic diet may cause deficiencies [...]. At the very least, individuals on a ketogenic diet should take some form of sugar free vitamin and mineral supplement to ensure nutritional adequacy. Additionally, supplemental sodium, magnesium and potassium may be necessary [...]. Depending on dairy intake, a calcium supplement may also be necessary.
A great deal of recent research is currently focusing on the benefit of various anti-oxidant nutrients such as vitamin C, vitamin E and beta-carotene. These substances, as well as many others, may help to prevent tissue damage from substances called ‘free radicals’. Free radicals are thought to damage cells causing the accumulation of toxic chemicals. Individuals involved in intense exercise appear to generate an excess of free radicals so supplementation may be indicated. Additionally, the few carbohydrates which are consumed on a ketogenic diet should come from a variety of vegetable sources whenever possible.
[...] a common side effect of ketogenic diets is a decrease in bowel movements. At least part of this is caused by the general lack of fiber in the ketogenic diet. For this reason, a sugar-free fiber supplement may be useful to maintain regularity. Additionally, the inclusion of high fiber vegetables, such as a large salad, can help with regularity in addition to the nutrients they provide.
Other suggested supplements: Essential fatty acids (EFAs), Omega-3 and omega-6 fatty acids and Olive oil
~ summary by L6S
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