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Effects of Dietary Beef and Soy Protein on Tissue Composition and Low Density Lipoprotein Uptake in Young Pigs^1,2,

Julie A. Johnson^*, Donald C. Beitz^*,,3 and Norman L. Jacobson

^* Department of Biochemistry-Biophysics Department of Animal Science, Iowa State University, Ames, IA 50011

To study effects of dietary protein source on plasma cholesterol homeostasis, six littermate pairs of 8-wk-old, castrated male pigs were assigned randomly to high fat diets containing either lean beef or soy protein isolate, with beef tallow as the major fat source in both diets. Diets were fed for 6 wk, with blood samples taken weekly and analyzed for lipid composition. At 6 wk, each pig was injected with [³H]cholesterol- and [¹⁴C]sucrose-labeled low density lipoproteins, and serial blood samples were taken. Pigs were then killed, and several tissues were sampled. Results show that dietary beef or soy protein, when fed with beef tallow as a fat source, has differential effects on rates of uptake of intact LDL by heart, M. sartorius muscle and subcutaneous adipose tissue, and on rates of uptake of LDL cholesterol by net free cholesterol exchange in subcutaneous and perirenal adipose tissues. Dietary protein source affected the composition of only two tissues analyzed. Pigs fed the beef-based diet had greater lipid concentrations in M. sartorius muscle, whereas pigs fed the soy protein-based diet had greater lipid concentrations in heart. Source of dietary protein did not influence in vivo kinetics of LDL cholesterol removal from blood plasma.

KEY WORDS: • cholesterol • atherosclerosis • low density lipoproteins • pig • beef protein • soy protein • radioactive isotopes

¹ Data taken from a thesis submitted to Iowa State University by J. A. Johnson as partial fulfillment of requirements for the M. S. degree. Journal Paper J-13069 of the Iowa Agriculture and Home Economics Experiment Station, Iowa State University, Ames, IA, Project No. 2735.

² Supported in part by the National Live Stock and Meat Board.

³ To whom correspondence should be addressed at 313 Kildee Hall, Iowa State University, Ames, IA 50011.

Manuscript received 2 December 1988. Revision accepted 21 February 1989.