Menopause-induced estrogen deficiency increases the risk of cardiovascular disease, which is related to a shift in regional fat distribution. We tested the hypothesis that estrogen-like isoflavones in soy protein isolate (SPI+) would lessen both regional fat gain and lean loss compared with isoflavone-poor soy (SPI−).
Perimenopausal participants (N = 69) were randomly assigned (double-blind) to 24 weeks of treatment (40 g soy or whey protein per day): SPI+ (n = 24), SPI− (n = 24), or whey control (n = 21); each participant had blood drawn in the fasted (12 hours) state, had physical activity assessed, and kept a 5-day food diary. Dual-energy x-ray absorptiometry was used to examine the effects of SPI+ on regional fat and lean tissue distribution changes in the waist, hip, and thigh regions.
Mean body mass increased (P < 0.01) in each group, but treatment had no effect on gain in overall body mass, fat mass, or lean mass using analysis of variance. In all treatment groups combined, lean mass increased in each region; fat mass increased only in the waist region. Treatment had an effect (P = 0.039) on hip lean mass and a marginal effect (P = 0.077) on thigh fat. Regression analyses revealed that SPI+ diminished the increase in thigh fat (P = 0.018) and heightened the increase in hip lean (P = 0.035) mass. Carbohydrate intake (P = 0.006) and cohort (reflective of season; P = 0.011) contributed to the gain in thigh fat. Total protein intake (P = 0.0012), plasma insulin (P = 0.0034), and physical activity (P = 0.047) contributed to the gain in hip lean mass.
Gain in hip lean mass was greater (P = 0.014) in SPI+ than other groups, but SPI+ did not reduce the disease-promoting menopausal shift in regional fat mass.
From the 1Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa; the 2Department of Food Science & Human Nutrition, Human Metabolic Unit, Center for Designing Foods to Improve Nutrition, and the Departments of 3Statistics and of 4Health and Human Performance, Iowa State University, Ames, Iowa; and the 5Department of Human Nutrition & Food Science, California State University at Pomona, Pomona, California.
Journal Paper 19453 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 3602, supported by Hatch Act and State of Iowa funds, USDA/Special Grant, and Iowa State University Research Grant.
Address reprint requests to D. Lee Alekel, PhD, RD, 1127 Human Nutritional Sciences Building; Department of Food Science & Human Nutrition, Iowa State University, Ames, IA 50011-1120. E-mail: firstname.lastname@example.org.