Effect of the Level of Dietary Protein with and without Added Cholesterol on Plasma Cholesterol Levels in Man

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Abstract
Sixty-five male university students were divided into two groups and given a formula ration providing protein and fat (butter) at levels of 15 and 30%, respectively, with or without a supplement of 500 mg cholesterol/950 Cal. for 8 days. The two groups were each divided into 5 sub-groups and transferred for another 8 days to diets in which the protein moiety was changed to 5, 10, 15, 20 and 25% by the addition or withdrawal of the protein preparation, calcium caseinate for equicaloric amounts of maltose-dextrins. Only the diets low in protein (5% of calories) caused a significant change in plasma cholesterol and this was in the form of an increase. The plasma cholesterol values in milligrams per 100 milliliters for these two groups fed the diets low in protein at day 8 and 16 were, respectively, 152.0 and 171.1 mg (+ 19.1, P < 0.05, without added cholesterol) and 168.3 and 180.2 (+ 11.9, P < 0.05, with added cholesterol). Thirty-two female students consumed the unsupplemented diet for 8 days. They were then divided into three groups and continued to receive for another 8 days diets, modified as described above, providing 5, 15, or 25% of calories as protein. The only significant change observed in the plasma cholesterol was a small but significant decrease in the case of the diet high in protein (- 7.4 mg/100 ml, P, 0.01 to 0.02). These data obtained from the first large scale experiment to be performed on normal young subjects fed a formula ration provide no support for the possibility that high intakes of protein per se are implicated in the development of cardiovascular disease through any elevating effect on plasma cholesterol levels.