protein for 9 weeks (18). Carbohydrate intake varied from 104 grams to 60 grams to 30 grams.
Although all three groups were in ketosis to some degree (especially during the first three weeks),
we will only consider that 30 and 60 carbohydrate gram diets as truly ketogenic diets.
Nitrogen balance was slightly negative during the first week of the diet. Approximately 2
grams of nitrogen were lost, equating to 13 grams of protein converted to glucose, meaning that
22 additional grams of protein would have been required to attain nitrogen balance. Added to the
115 grams of protein given, this yields a total of 137 grams of protein to prevent all nitrogen
losses. Nitrogen balance was achieved during week 2 and became slightly positive during the
third week.
In a third study, which examined the metabolic effects of a variety of different dietary
approaches, subjects were studied under a total of 6 different dietary conditions (19). We are only
concerned with three of them. The first was a 400 calorie diet consisting of 100 grams of protein.
In this group the average negative nitrogen balance was -2 grams, the equivalent of 12 grams of
body protein broken down to make glucose. An additional 20 grams of dietary protein (for a total
of 120 grams/day) would have provided this amount of glucose and prevented any nitrogen losses.
When you consider that even 100 grams of protein was unable to prevent nitrogen losses, it is no
surprise that studies using less protein (often only 50 grams per day) than this fail to show
nitrogen sparing with ketogenic diets.
The second dietary approach we are concerned with was a group given 800 calories as 200
grams of protein. In this group, there was a positive nitrogen balance of almost 8 grams/day, the
equivalent of 48 grams of protein. This suggests that a protein intake of 152 grams would have
been sufficient to achieve nitrogen balance, supporting the value of 150 grams from the previous
section.
A third group was given 400 calories of protein and 400 calories of fat and showed the
same negative nitrogen balance as the 400 calories of protein only. This points out that the fat
intake/calorie level of a ketogenic diet does not affect nitrogen balance. Meaning that, protein
calories are far more important than fat calories in terms of achieving nitrogen balance on a
ketogenic diet.
This study is interesting as it shows that nitrogen balance can be attained essentially
regardless of calorie level as long as sufficient protein intake is consumed, as has another study
(20). The difference between the two values for protein intake determined in this study (120
grams and 152 grams) cannot be explained from the data presented.
Do ketogenic diets spare more nitrogen than non-ketogenic diets?
A lack of well done studies makes this question difficult to answer unequivocally. As
mentioned above, the problem is that many studies are very short, generally a few days to a few
weeks. As the studies discussed above show (and discussed in detail in chapter 5), a minimum of
3 weeks is required for the protein sparing adaptations to ketosis to occur.
Most studies comparing ketogenic to non-ketogenic diets are done at very low calorie levels
(VLCD, below 600 cal/day). These have limited applicability to an individual dieting at 10-20%
below maintenance levels as advocated in this book for reasons discussed in detail below.