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Comparison of Dietary Casein or Soy Protein Effects on Plasma Lipids and Hormone Concentrations in the Gerbil (Meriones unguiculatus)^1,2,

Department of Nutrition, School of Public Health, University of North Carolina-Chapel Hill, Chapel Hill, NC 27514

The effects of dietary animal protein (casein) or soy protein (soy isolate) on plasma lipids and hormones were investigated in the gerbil. Diets, fed to male gerbils (intial weight, 60 g) for 4 wk, contained either 18% casein or soy isolate as the protein source. The dietary fat sources were lard (16%) and safflower oil (1%). The cholesterol content of the diet was 0.1%. Plasma total cholesterol concentrations were lower in gerbils fed the soy protein diet (159 mg/dl) than in the gerbils fed the casein diet (190 mg/dl). Absolute HDL-cholesterol concentrations were unaffected by the protein source, but LDL-cholesterol concentrations were lower in the soy-fed gerbils. Thus, the ratio of LDL to HDL cholesterol was lower in the soy-fed gerbils (0.42) compared with the casein-fed gerbils (0.70). Plasma insulin levels were higher in the soy-fed gerbils as were plasma thyroxine and thyroid-stimulating hormone levels. The results indicate that the gerbils can be used to study dietary effects on cholesterol parameters. These data also suggest that changes in plasma thyroxine levels may in part account for the hypocholesterolemic effect of soy protein.

KEY WORDS: • casein • soy protein • cholesterol • insulin • glucagon • thyroid hormones

¹ This work was supported in part by National Institutes of Health Biomedical Research Support Grant RR05450.

² A preliminary report of these data was presented at the 1983 Federation of American Societies for Experimental Biology meetings in Chicago, IL. Forsythe, W. A., III (1983) Dietary protein source effects on plasma lipid and hormone concentrations in the gerbil (abs. 4483), Fed. Proc. 42, 1057.

Manuscript received 25 October 1985. Revision accepted 19 February 1986.