individuals have little trouble maintaining their bodyfat levels when the ketogenic diet is stopped,
especially if their activity patterns are maintained.
Appetite suppression
An unusual effect of complete fasting is a general decrease in appetite after a short period
of time. Additionally, studies which restrict carbohydrate but allow ‘unlimited’ fat and protein find
that calorie intake goes down compared to normal levels further suggesting a link between
ketosis and appetite (10,11).
Since continued fasting causes an increase in ketone bodies in the bloodstream, achieving
a maximum in 2-3 weeks, it was always assumed that ketones were the cause of the appetite
suppression (12). As with many aspects of ketosis (in this case starvation ketosis), this
assumption was never directly studied and propagated itself through the literature without
challenge. Recent research indicates that ketones per se are most likely not the cause of the
decreased appetite during ketosis.
As discussed in chapter 9, several studies have shown an automatic decrease in caloric
intake (and presumably appetite) when individuals restrict carbohydrates to low levels, despite
being told to eat ‘unlimited’ amounts of fat and protein. In one study the ketogenic diet
suppressed appetite moreso than a balanced diet where an appetite suppressant was given (13).
Several studies have compared appetite on a very low calorie (below 800 calories/day)
ketogenic diet versus appetite on a balanced diet with the same calories (14,15). In general, no
difference was seen in appetite between the two diets. This leads researchers to think that
ketones do not blunt appetite in and of themselves. Rather two possible mechanisms seem a
more likely explanation for the appetite blunting seen with a ketogenic diet.
First, is the relatively higher fat content of the ketogenic diet compared to other diets. Fat
tends to slow digestion, meaning that food stays in the stomach longer, providing a sense of
fullness. The same has been shown to for protein (14). Additionally, protein stimulates the
release of the hormone cholecystokinin (CCK) which is thought to help regulate appetite.
However, studies using very-low-calorie intake (and hence low dietary fat intakes) have
documented this same blunting of appetite, suggesting a different mechanism. Rather than the
effects of dietary fat, the researchers argue that what is perceived as a blunting of appetite is
simply a return to baseline hunger levels.
That is, during the initial stages of a diet, there is an increase in appetite, which is followed
by a decrease over time. It is this decrease which is being interpreted by dieter’s as a blunting of
appetite (14,15).
Overall, the data supporting an appetite suppressing effect of ketogenic diets points to a
mechanism other than ketones. This is not to say that appetite may not be suppressed on a
ketogenic diet, only that it is most likely not ketones or metabolic ketosis which are the cause of
the suppression.
Anecdotally, some individuals have a strong suppression of appetite while others do not.
This discrepancy can probably be ascribed to individual differences. If a dieter’s appetite is
suppressed substantially on a ketogenic diet, it may be difficult for them to consume the