Additionally, since the major adaptations to ketosis (especially with regards to protein
sparing) take at least 3 weeks to occur, studies shorter than three weeks in duration may
erroneously conclude that the ketogenic diet provides no benefit in terms of protein sparing
compared to a balanced diet (13). Invariably these studies show a gradual improvement in
nitrogen balance over three weeks suggesting that the ketogenic diet might have the benefit in
terms of protein sparing in the longer term (13). Since most dieters do not diet for only three
weeks, longer term changes in nitrogen balance are more important than short term.
Most diet studies are done at extremely low calorie levels, generally less than 800 calories
per day (referred to as a very-low-calorie-diet or VLCD). Although the dietary fat intake has little
effect on nitrogen sparing, the low calorie nature of most studies has an important implication: to
keep calories very low, protein intake must also be low.
Research has established that a minimum protein intake of 1.5 grams protein/kg ideal
body weight is necessary to achieve nitrogen balance (2,14). However, some studies provide as
little as 50 grams of protein per day, drawing erroneous conclusions about the nitrogen sparing
effects of ketogenic diets (15). When protein intake is inadequate to begin with, extra
carbohydrate is significantly protein sparing, especially in the first three weeks while the
adaptations to ketosis are occurring (15). But given adequate protein, carbohydrates appear to
have no additional nitrogen sparing effect.
As the following data shows, providing adequate protein from the first day of even a VLCD
ketogenic diet should prevent any loss of nitrogen. The calculations presented in the last section
suggest that 150 grams of protein per day should be used during at least the first three weeks of
a ketogenic diet. The available studies are examined to see if this value is correct.
How much protein is needed to prevent nitrogen loss?
Having examined this question theoretically in the previous section, we can examine a few
studies to see if the suggested 150 grams of protein per day is correct. Since only a few studies
provided an appropriate amount of protein to its subjects, we will look at these studies in detail.
In a maintenance calorie diet study, six subjects were given 2,800 calories with 135 grams
of protein, 40 grams of carbohydrate and 235 grams of fat for a period of 6 days (15). This was
compared to a diet containing 135 grams of protein, 40 grams of fat, and 475 grams of
carbohydrate. Both diet groups were in positive nitrogen balance from the first day of the study.
As well, the 40 grams of carbohydrate in the ketogenic group spared some protein breakdown. It
would be expected that a lower carbohydrate intake would require a larger intake of protein to
avoid nitrogen losses.
In a second maintenance calorie diet study, subjects received 1.75 g protein/kg ideal body
weight daily (17). Nitrogen balance was attained in most subjects by the second week of the
study. However, since the study did not list how many grams of protein were given to each
subject, it is impossible to determine how much additional protein would have been needed to
establish nitrogen balance from the first day. This study simply supports the idea that nitrogen
balance can be attained quickly on a ketogenic diet, provided that sufficient protein is consumed
In another study, eight men were placed on diets of 1800 calories, containing 115 grams of