Chapter 5:
Adaptations to Ketosis
Having discussed the basics of fuel utilization, ketone body formation and ketosis, it is now
time to examine in detail the adaptations which occur in shifting the body away from glucose and
towards fat metabolism. The primary adaptation occurs in the brain although other systems are
affected as well.
There is a common misconception, especially among bodybuilders, that ketosis is
indicative of protein breakdown when in fact the exact opposite is the case. The development of
ketosis sets in motion a series of adaptations which minimize body protein losses during periods
of caloric deprivation. In fact, preventing the development of ketosis during these periods
increases protein losses from the body.
The adaptations to ketosis are complex and involve most systems of the body. As with the
previous sections, smaller details are ignored for this discussion and interested readers should
examine the references provided. Rather, the major adaptations which occur in the body’s
tissues, especially the brain, liver, kidney and muscle are described
The adaptations to ketosis have been studied in great depth during periods of total
starvation. While this is an extreme state, the lack of food intake makes it simpler to examine
the major adaptations. To help individuals understand the adaptations to ketosis, the
metabolism of the body is examined during both short and long term fasting. The next chapter
discusses the effects of food intake on ketosis, as well as body composition changes. The following
sections address in detail the effects of ketosis on glucose/protein requirements as well as the
effects on fat and ketone use.
Section 1: An overview of starvation
Starvation and the ketogenic diet
In one sense, the ketogenic diet is identical to starvation, except that food is being
consumed. That is, the metabolic effects which occur and the adaptations which are seen during
starvation are roughly identical to what is seen during a ketogenic diet. The primary difference is
that the protein and fat intake of a ketogenic diet will replace some of the protein and fat which
would otherwise be used for fuel during starvation.
The response to total starvation has been extensively studied, arguably moreso than the
ketogenic diet itself. For this reason the great majority of data presented below comes from
studies of individuals who are fasting. With few exceptions, which are noted as necessary, the
metabolic effects of a ketogenic diet are identical to what occurs during starvation.
Although it is discussed in greater detail in a later section, the critical aspect of developing
ketosis is the quantity of carbohydrates in the diet and carbohydrate restriction mimics the