obese subjects lost weight on a 2600 calorie high fat diet but lost noweight when put on a 2000 calorie higher carbohydrate diet (29,30). As these studies attemptedto measure changes in lean body mass as well, they concluded that large amounts of fat werebeing lost on the high fat, but not the high-carbohydrate diets.As would be expected, results of this nature were far too good to be true. The very short61term nature of the studies, 9 days or less, as well as the rapid weight loss which occurred in thefirst few days of the high fat diets, indicate that the supposed fat loss which was occurring wascoming primarily from changes in water balance (33,34), which can contribute anywhere from 5to 15 lbs of weight loss within a few days (see next section). Later studies using the sameexperimental design, determined that the weight lost and counted as fat was water and that therewas no metabolic advantage to low carbohydrate diets in terms of weight loss (35,36).Water loss on the ketogenic dietA well established fact is that low-carbohydrate diets tend to cause a rapid loss of water inthe first few days. This occurs for several reasons. First and foremost, glycogen is stored alongwith water in a ratio of three grams of water for every gram of stored carbohydrate (37). Asglycogen is depleted, water is lost. For large individuals, this can represent a lot of weightElectrolyte excretion is discussed in greater detail in the next chapter.Due to confusions about weight loss and fat loss (see chapter 8), many individuals aredrawn to low-carbohydrate diets specifically for the rapid initial loss of water weight. During thefirst few days of a ketogenic diet, water loss has been measured from 4.5 to 15 lbs (17,39-41).Although transient, this rapid initial weight loss can provide psychological incentive fordieters, which may mean greater compliance with the diet. In one study of subjects on a verylow-calorie ketogenic diet adhered to their diet much more than individuals consuming morecarbohydrate, and who lost less weight (8).Regardless of possible psychological benefits, it should be understood that the initial weightloss on a ketogenic diet is water. This is especially critical for when individuals come off of aketogenic diet, either deliberately or because they cheated. The rapid weight gain which occurswhen carbohydrates are reintroduced into the diet, which can range from three to five pounds inone day, can be as psychologically devastating to dieters as the initial weight loss was beneficial.In the same way that fat cannot be lost extremely rapidly, it is physiologically impossible to gainthree to five pounds of true bodyfat in one day. This is discussed in more detail in chapter 14 .A final thing to note is that this water loss can be misinterpreted as a loss of proteincontaininglean body mass (LBM), depending on the method of measurement. (8). This may bepart of the reason that some studies find report a greater loss of LBM for ketogenic versus nonketogenicdiets.Weight lossThe fact that the initial weight loss on a ketogenic diet is from a loss of water weight hasled to a popular belief that the only weight lost on a ketogenic diet is from water, an attitude thatmakes little sense. The question then is whether more or less true weight (i.e. non-water) is loston a ketogenic diet versus a non-ketogenic diet.62In most studies, a low-carbohydrate diet will show a greater total weight loss than a highcarbohydrate(8,18,19,25,26,35) but this is not always the case (10,13,15,22) . Once water losshas been taken into account, the rate of weight loss seen, as well as the total weight loss isgenerally the same for ketogenic versus non-ketogenic diets (35,40). That is, if individuals are puton a 1200 calorie per day diet, they will lose roughly the same amount of true weight (notincluding water) regardless of the composition of the diet. As discussed in chapter 2, a loss ofweight is not the sole goal of a diet. Rather the goal is maximization of fat loss with aminimization of muscle loss.Section 5: Fat lossThe basic premise of the ketogenic diet is that, by shifting the metabolism towards fat useand away from glucose use, more fat and less protein is lost for a given caloric deficit. Given thesame total weight loss, the diet which has the best nitrogen balance will have the greatest fatloss. Unfortunately a lack of well done studies (for reasons discussed previously) make thispremise difficult to support.Before discussing the studies on ketogenic diets, a related approach, called the proteinsparing modified fast (PSMF) is discussed. Following that, changes in body composition arediscussed at three calorie levels: maintenance calories, below 1200 calories per day, and finallybetween 10% below maintenance and 1200 calories per day.The PSMFThe PSMF is a ketogenic regimen designed to maximize fat loss while minimizing proteinlosses. The sole source of calories are lean proteins which provide 1.5 grams of protein perkilogram of ideal body mass (which is used to estimate lean body mass) or approximately 0.7-0.8grams of protein per pound. (14,20,42-44). Vitamins and minerals are given to avoid theproblems discussed in chapter 7 and no other calories are consumed (42,44).The total caloric intake of the PSMF is extremely low, generally 600-800 calories per dayor less. Once the adaptations to ketosis have occurred, the remainder of the days caloricrequirements are derived from bodyfat. For an average size male, with a basal metabolic rate of2700 calories per day, this may represent 2500 calories or 280 grams of fat (approximately 0.7 lbof fat) used per day.Fat losses of 0.2 kilograms/day (0.45 lbs) in women and 0.3 kilograms/day (0.66 lbs) in mencan be achieved and weight losses of three to five pounds per week are not uncommon (44,45).This can be achieved with only small losses of protein, which occur primarily during the first threeweeks while the adaptations to ketosis are occurring.Additionally, appetite tends to be blunted in some individuals, making adherence easier.Finally, there are typically improvements in blood pressure, blood glucose, and blood lipids whileon the PSMF (44). These effects make the PSMF is a very attractive approach for fat loss.However, the PSMF has drawbacks which make it unsuitable for do-it-yourself dieters.63