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 non-
ketogenic 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 low-
carbohydrate, 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