Effect of a daily supplement of soy protein on body composition and insulin secretion in postmenopausal women

ObjectiveTo determine whether a supplement of soy protein improves body composition, body fat distribution, and glucose and insulin metabolism in postmenopausal women without diabetes compared with an isocaloric casein placebo.DesignRandomized, double-blind, placebo-controlled 3-month trial.SettingClinical Research Center.Patient(s)Fifteen postmenopausal women.Intervention(s)Computed tomographic scans at L4/L5, dual energy x-ray absorptiometry, hyperglycemic clamps.Main Outcome Measure(s)Total fat, total abdominal fat, visceral fat, subcutaneous abdominal fat, and insulin secretion.Result(s)Weight by dual energy x-ray absorptiometry did not change between groups (+1.38 ± 2.02 kg for placebo vs. +0.756 ± 1.32 kg for soy, mean ± SD). Total and subcutaneous abdominal fat increased more in the placebo group than in the soy group (for differences between groups in total abdominal fat: +38.62 ± 22.84 cm2 for placebo vs. −11.86 ± 31.48 cm2 for soy; subcutaneous abdominal fat: +22.91 ± 28.58 cm2 for placebo vs. −14.73 ± 22.26 cm2 for soy). Insulin secretion, visceral fat, total body fat, and lean mass did not differ between groups. Isoflavone levels increased more in the soy group.Conclusion(s)A daily supplement of soy protein prevents the increase in subcutaneous and total abdominal fat observed with an isocaloric casein placebo in postmenopausal women.