Effects of the source of dietary protein on serum lower density lipoprotein (VLDL + LDL) and tocopherol levels in female rats.

The effect of dietary protein on lipid levels of serum and liver and mineral contents of bone tissue was studied in female rats by using 13 semi-purified diets differing with respect to protein source. The diets were characterized with regard to contents of protein, amino acids, fat, crude fiber, phytate, zinc, copper, iron, magnesium, calcium, sodium, potassium, tocopherol and metabolizable energy. Six of the proteins tested were of animal origin and six proteins used were plant proteins. Each diet was fed at a 20% protein, 10% fat level. There was a large variation between groups in the serum content of lower density lipoproteins (VLDL + LDL). Rats fed plant protein diets showed values in a lower range than rats consuming animal protein diets. Triglyceride values showed a similar tendency. A comparison of dietary amino acid composition and blood lipid parameters revealed a significant negative correlation between dietary arginine content and serum VLDL + LDL levels (r = 0.863; P < 0.01). Group differences in total serum cholesterol were also observed. However, this variation was within the same range in animal as well as plant protein diets. Serum tocopherol levels were correlated to the total dietary intakes of tocopherol. No significant trend was observed for the mineral content of bone tissue or for the total lipid content of liver with regard to class of dietary protein. However, all rats fed a blood protein diet developed fatty livers.