All that can be said from most of these studies is that a non-ketogenic diet will spare
nitrogen better than a ketogenic diet as long as the diet periods are less than three weeks
(13,16,19,21). The problem being that diets are rarely used for a period as short as three weeks
in the real world. Some studies show greater nitrogen sparing for the ketogenic diet (22-24) while
others show no advantage (21,23,25) and others show less nitrogen sparing (13,15,26).
At higher calorie levels (maintenance to 1200 calories), there are few studies. One study
at 1200 calories found less lean body mass (LBM) loss for the higher carbohydrate diets (27)
while another found no difference in LBM losses (28). A final study done at 1800 calories found
less nitrogen sparing for the ketogenic diet during the first three weeks of the diet but greater
nitrogen sparing during the last three weeks of the diet (18).
Summary
Arguably the most critical aspect to prevent nitrogen losses on a ketogenic diet is the
consumption of adequate protein. It should be noted that there is great variability in how well
people spare protein on a ketogenic diet. On average it appears that a protein intake of at least
120-150 grams per day should be sufficient to maintain nitrogen balance, regardless of calorie
levels. However, this value does not include any additional protein needed to cover exercise, and
none of these studies have discussed weight training individuals. This topic of exercise and
protein requirements is discussed in chapter 9.
It is difficult to draw any good conclusions about the relative effects on protein sparing for
ketogenic versus non-ketogenic diets. The general study designs, incorporating very short study
periods, very low calories and inadequate protein make it impossible to draw conclusions for an
individual dieting at twenty percent below maintenance calories, with adequate protein, and who
is exercising. The limited studies done at higher calorie and higher protein levels suggest that the
ketogenic diet is no worse in terms of protein sparing than a non-ketogenic diet, assuming that
adequate protein is given. One study suggests that protein sparing is better as long as adequate
protein is given and the adaptations to ketosis are allowed to occur.
Anecdotal evidence suggests that there is great variety in muscle loss when individuals
diet. Many individuals can avoid muscle loss effectively with any number of diets while others
find that muscle losses are much less on a ketogenic diet compared to a more balanced diet. By
the same token, some individuals find that their muscle loss is greater on a ketogenic diet versus
a more traditional diet.
The implication of the above data is this: if an individual finds that they lose too much
muscle on a balanced diet, with a reasonable deficit, and adequate protein, a ketogenic diet may
be worth trying. By corollary, if an individual finds that they are losing lean body mass on a
ketogenic diet (as indicated by changes in body composition measurements or consistent losses of
strength in the gym), and protein intake is adequate, it should be concluded that the adaptations
to ketosis are not sufficient to prevent protein losses and a more ‘balanced’ dietary approach
should be tried.