In most studies, a low-carbohydrate diet will show a greater total weight loss than a high-
carbohydrate (8,18,19,25,26,35) but this is not always the case (10,13,15,22). 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 (35,40). 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. As discussed in chapter 2, a loss of
weight is not the sole goal of a diet. Rather the goal is maximization of fat loss with a
minimization of muscle loss.
Section 5: Fat loss
The basic premise of the ketogenic diet is that, by shifting the metabolism towards fat use
and away from glucose use, more fat and less protein is lost for a given caloric deficit. Given the
same total weight loss, the diet which has the best nitrogen balance will have the greatest fat
loss. Unfortunately a lack of well done studies (for reasons discussed previously) make this
premise difficult to support.
Before discussing the studies on ketogenic diets, a related approach, called the protein
sparing modified fast (PSMF) is discussed. Following that, changes in body composition are
discussed at three calorie levels: maintenance calories, below 1200 calories per day, and finally
between 10% below maintenance and 1200 calories per day.
The PSMF
The PSMF is a ketogenic regimen designed to maximize fat loss while minimizing protein
losses. The sole source of calories are lean proteins which provide 1.5 grams of protein per
kilogram of ideal body mass (which is used to estimate lean body mass) or approximately 0.7-0.8
grams of protein per pound. (14,20,42-44). Vitamins and minerals are given to avoid the
problems 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 day
or less. Once the adaptations to ketosis have occurred, the remainder of the day’s caloric
requirements are derived from bodyfat. For an average size male, with a basal metabolic rate of
2700 calories per day, this may represent 2500 calories or 280 grams of fat (approximately 0.7 lb
of 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 men
can 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 three
weeks 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 while
on 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.