Effect of soy protein and isoflavone level in diets on blood hormones in postmenopausal women

It has been postulated that soy protein and/or a component of soy protein lowers blood cholesterol concentration by influencing circulating hormone levels. Therefore, this study was designed to determine whether or not soy protein containing low or moderate levels of isoflavones mediated changes in hormones involved in lipid metabolism. Seventy-one hypercholesterolemic postmenopausal women were investigated during a twenty-four week parallel group study with three intervention arms. Initially subjects were placed on a low fat, low cholesterol NCEP Step I diet for two weeks and then randomly assigned to a treatment group. Subjects then maintained the NCEP Step I diet and consumed 40g protein/day from either soy protein isolate containing 0.8mg isoflavones/g protein, soy protein isolate containing 1.6mg isoflavones/g protein, or casein/nonfat dry milk containing no isoflavones. The test proteins were incorporated into baked products and/or drinks. At baseline. 12 weeks, and 24 weeks, serum or plasma was measured for triiodothyronine (T3), T3 uptake, thyroxine, thyroid stimulating hormone (TSH), insulin, glucagon, and cortisol. Results will be presented. (Funded by the Illinois Soybean Program Operating Board).