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

Abstract

Objective: To 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.

Design: Randomized, double-blind, placebo-controlled 3-month trial.

Setting: Clinical 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 cm(2) for placebo vs. -11.86 +/- 31.48 cm(2) for soy; subcutaneous abdominal fat: +22.91 +/- 28.58 cm(2) for placebo vs. -14.73 +/- 22.26 cm(2) 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.

Figures

Figure 1

Effect of soy isoflavones on body composition and body fat distribution in women randomized to placebo or soy isoflavones. Values are means ± S.D. A) There were no differences between placebo and soy isoflavones in changes in total body fat or lean body mass as measured by DXA. B) Soy isoflavones prevented the gain in subcutaneous abdominal fat and total abdominal fat compared to an increase with placebo as measured by CT scan (differences between groups based on unpaired t-test, p=0.013 for subcutaneous abdominal fat and p=0.005 for total abdominal fat). There were no differences between groups in BMI or in visceral fat.

Figure 2

Effect of soy isoflavones and placebo on insulin secretion. Values are means ± S.D. A, B) There were no differences within groups in first or second phase insulin secretion with soy isoflavones or with placebo (differences within groups based on paired t-test). C) There were no differences between groups in the area under the curve (AUC) in pmol/min for first or second phase insulin secretion (differences between groups based on unpaired t-test).

Figure 3

Serum isoflavone levels at baseline and changes with placebo versus soy isoflavones. Values are means ± S.D. A) There were no differences in serum isoflavone levels between groups at baseline. B) There were significant increases during the study in daidzein (p=0.004), dihydrodaidzein (DHD, p=0.002), O-desmethylangiolensin (O-DMA, p=0.03), genistein (p=0.01), glycitein (p=0.005), (differences between groups based on unpaired t-tests). There were no differences between groups in equol levels (p=0.17).