Effect of Soy Bread on Markers of Bone Metabolism and Cardiovascular Disease

Overview

A study was designed with two specific aims: (1) to assess the effect of soy bread, compared with wheat bread, on markers of bone metabolism and cardiovascular health, and (2) to evaluate whether soy bread consumption affects the metabolism of phytoestrogens. To answer Aim 1, a double-blind randomized crossover trial was conducted. Individuals with an ability to metabolize a specific isoflavone, daidzein, consumed 3 slices of bread (either soy or wheat) daily over a 12-week period. After a 4-week wash-out period, subjects consumed 3 slices/day of the other type of bread. Markers of bone metabolism and cardiovascular health were evaluated before and after each time period. To answer Aim 2, individuals who did not metabolize daidzein at baseline entered a double-blind randomized trial of soy bread with or without fructooligosaccharide (a type of dietary fiber) over an 8-week period. Subjects were evaluated regarding their ability to metabolize daidzein to equol.

Soy beans are rich in isoflavones, such as genistein and daidzein, which exhibit estrogenic activity. While the cardiovascular benefits of isoflavones in soy have been recognized, the effects on bone metabolism are less well known. The National Aeronautics and Space Administration expressed an interest in the effects of soy on bone loss and a former NASA scientist developed a soy product, soy bread, which may be more palatable for most Americans than currently available soy foods. A two-treatment two-period crossover trial was conducted to assess the effects of soy bread consumption on deoxypyridinoline, N-telopeptides, bone-specific alkaline phosphatase, osteocalcin, calcium, leptin, insulin-like growth factor-1, luteinizing hormone, follicle-stimulating hormone, testosterone, cholesterol (total, HDL, LDL), triglycerides, apolipoprotein AI, apolipoprotein B, C-reactive protein, and glycosylated hemoglobin. The crossover trial was conducted in subjects identified as having the ability to metabolize daidzein to equol. The treatment was 3 servings of soy bread daily over a 12-week period. The control period included 3 servings of a placebo wheat bread over a 12-week period. For subjects who did not metabolize daidzein to equol at baseline, a pretest-posttest trial of soy bread consumption over an 8-week period was conducted to examine whether 3 servings/day of soy bread increased urinary equol concentrations and whether the addition of fructooligosaccharide enhanced this excretion.