Section 4: Water and weight loss Having discussed the topic of nitrogen sparing we can finally examine the effects of ketogenic diets on the other aspects of body composition: water, weight and fat loss. The question then to be answered is whether a ketogenic diet will cause more weight and/or fat loss than a nonketogenic diet with the same calories. As with the sections on protein sparing, study methodology makes makes it impossible to absolutely answer this question. Prior to discussing the effects of the ketogenic diet on body composition, a few comments about the various studies cited by both the pro- and anti-ketogenic groups are in order.
Problems with the studies Most of the early ketogenic diet studies looked at weight loss only, making no distinction between fat, water and muscle loss. As discussed in chapter 8, a dieter’s goal should be maximal fat loss with minimal muscle loss. Since water weight can be gained or lost quickly, it should not be used as the factor to determine whether a ketogenic or balanced diet is the optimal approach. Likewise, many early studies, which are frequently cited by pro-ketogenic authors, confused water loss with fat loss due to methodological problems. These studies should not be considered as evidence either for or against a ketogenic diet. Many early diet studies were extremely short in duration, five to ten days in some cases. This makes drawing valid conclusions about the effectiveness of a given diet approach impossible as results are confounded by the rapid water losses which occurs in the first few days. In very short term studies, a ketogenic diet will almost always show greater weight loss because of fluid losses. However, the amount of fat loss which can occur in this period of time is negligible in almost any diet study. As well, since few dieters pursue fat loss for only 10 days, studies of this duration have limited applicability.
The early studies A number of studies done in the 50’s and 60’s showed almost magical results from lowcarbohydrate, high-fat diets. The primary result was significantly greater weight loss for low versus high carbohydrate diets in obese subjects (29,30). This led researchers involved to conclude that there was an enhancement of metabolism with the high fat diets, a sentiment echoed by some popular diet book authors. It was suggested that ketogenic diets caused the secretion of a ‘fat mobilizing substance’ which enhanced fat loss (31,32), but this substance was never identified. In these studies, obese subjects lost weight on a 2600 calorie high fat diet but lost no weight when put on a 2000 calorie higher carbohydrate diet (29,30). As these studies attempted to measure changes in lean body mass as well, they concluded that large amounts of fat were being 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 short 61