still provide 18 grams of glucose per day, protein breakdown will only be 20 grams per day (see
table 2 on the next page) (6). As stated previously, is appears the primary purpose of ketones in
humans is to provide the brain with a non-glucose, fat-derived fuel for the brain (27,30).
Summary
The implication of the adaptations discussed above is that the body does not require
dietary carbohydrates for survival (exercise and muscle growth are a separate issue). That is,
there is no such thing as an essential dietary carbohydrate as the body can produce what little
glucose it needs from other sources.
Of course, the price paid is the loss of body protein, which will ultimately cause death if
continued for long periods of time. This loss of body protein during total starvation is
unacceptable but the above discussion only serves to show that the body goes through a series of
adaptations to conserve its protein. As we see later in this chapter, the addition of dietary
protein will maintain ketosis, while preventing the breakdown of bodily protein. In brief, rather
than break down bodily protein to produce glucose, the body will use some of the incoming dietary
protein for glucose production. This should allow maximal fat utilization while sparing protein
losses.
Table 2: Sources of glucose during long term starvationSource Glucose produced (grams)
Amount of carbohydrate required by brain ~40
Breakdown of 180 grams of fat 18
Breakdown of 20 grams of protein 20
Total carbohydrate produced per day 38
in the liver and kidneySection 4: Ketosis and protein sparing
Having quantitatively examined the adaptations which occur in terms of glucose use and
nitrogen losses during starvation, the mechanisms behind the ‘protein sparing’ effect of ketosis
can now be discussed.
The question which needs to be answered is what mechanisms exist for ketones (or
ketosis) to spare protein. There are at least four possible mechanisms through which ketogenic
diets may spare protein, three of which are well established in the literature, the fourth less so.
They are discussed in more detail below.
Decreasing the body’s glucose requirements
This is arguably the primary mechanism through which ketosis spares nitrogen losses.
This adaptation is discussed in detail in the previous sections and is well established in the