Why the discrepancy between VLCD research and moderate caloric deficits?
The discrepancy between research on diets with extreme caloric deficits versus those with
more moderate deficits is perplexing. At first glance it would seem that the greater the caloric
deficit, the more fat which should be lost. However in practice, even with sufficient dietary
protein, this is rarely the case, especially in the first few weeks of a diet. Although the reasons for
this discrepancy are unknown, some speculation is warranted.
It appears that there are certain caloric thresholds beyond which the physiological
responses to diet and exercise change. As discussed in chapter 22, exercise has its greatest
impact in increasing fat loss and decreasing muscle loss with moderate caloric deficits. (51) Once
calories are reduced below a certain point, exercise generally stops having a significant effect.
It may also be that once calorie levels fall below a certain level, there is increased muscle
loss regardless of diet, especially in the first few weeks. That is, for reasons which are not entirely
understood, the body appears to be limited in the quantity of fat it can breakdown without some
loss of protein (52). This makes it difficult to measure significant differences in bodyfat and
protein losses, simply because they are so high in both ketogenic and non-ketogenic VLCDs.
This speculation is consistent with studies on metabolic rate showing a much larger
decrease in metabolic rate once calories reach a certain low level (53,54). Hence this book’s
recommendation to use moderate caloric restriction with exercise. It is interesting that the study
done with the highest caloric intake (1800 calories/day) showed the most significant differences in
fat and weight loss ; but more research is needed at this calorie level.
Along with this is the issue of inadequate protein, discussed previously in this book. The
low-calorie nature of the VLCD mandates low protein levels. With only 400 calories per day, the
maximum amount of protein which could be consumed would be 100 grams, still lower than the
150 grams required to prevent all nitrogen losses determined in the last chapter. Low protein
intake may be one cause of the decrease in metabolic rate with VLCDs (55) and it seems
reasonable that this could have an impact on fat loss/LBM loss as well.
Summary
The effects of the ketogenic diet on weight and water loss are fairly established. In general,
due to the diuretic nature of ketones, total weight and water loss will generally be higher for a
ketogenic diet compared to a non-ketogenic diet. However, once water losses, which may
represent a weight loss of 5 pounds or more, are factored out, the true weight loss from a
ketogenic diet is generally the same as for a non-ketogenic diet of the same calorie level. This is
especially true at low calorie levels.
The research on fat and LBM losses are more contradictory and may be related to calorie
level. At maintenance calories, fat loss will not occur. At extremely low calorie levels, below 1200
per day and lower, there are some studies suggesting that a ketogenic diet causes more fat/less
LBM loss than a non-ketogenic diet while other studies support the opposite. In all likelihood, the
differences are due to variations in study design, protein intake, study length, etc. Because these
studies do not mimic the types of ketogenic diets described in this book, with a moderate caloric