COMBINED EFFECTS OF DIETARY-PROTEIN AND FAT ON LIPID-METABOLISM IN RATS

The combined effects of dietary protein (casein, whey protein, or soy protein) and fat (safflower oil, perilla seed oil, or their mixed oil; linoleic acid/a-linolenic acid=5.0) on several lipid parameters were studied in rats. Serum cholesterol and triglyceride levels were lower in perilla seed oil groups irrespective of the protein sources. Liver triglyceride level, and fecal excretion of steroids were influenced ma inly by protein sources, particularly isolated soy protein lowered liv er triglyceride level, and increased the fecal steroid excretion. The fatty acid composition of liver phosphatidylcholine was influenced by dietary fat sources., The proportion of arachidonic acid was significa ntly lower in rats fed perilla seed oil than in those fed safflower oi l or mixed oil, while the proportion of eicosapentaenoic acid was high er in rats fed perilla seed oil than in those fed safflower oil. Arach idonic acid/linoleic acid ratio was significantly lower in perilla see d oil groups, and tended to be higher in casein groups. Eicosapentaeno ic acid/arachidonic acid ratio was influenced by both dietary protein and fat, and protein-fat interaction was observed. Eicosapentaenoic ac id/arachidonic acid ratio was higher in perilla seed oil groups, and i solated soy protein in perilla seed oil groups lowered the ratio in co mparison with other protein sources in perilla seed oil groups.