Effects of 16 weeks of isoflavone‐rich soy protein on weight and fat gain in female college students

Abstract

Human intervention trials aimed at reducing weight gain and body fat using soy protein and isoflavones are few in number and show equivocal results. The objective of this study was to compare the effects of a daily isoflavone‐rich soy‐based meal replacement versus a casein‐based control on body weight and fat gain over 16 weeks in 18–19 year old female college freshmen (N = 120). Participants were randomized to treatment group (soy or casein) in this double‐blind, placebo‐controlled trial. Fat mass (FM), fat‐free soft tissue mass (FFST) and % body fat (%BF) were measured using dual energy X‐ray absorptiometry (Delphi 4500). A 2 x 3 RM‐ANOVA was used to measure the response of the dependent variables (body weight, FM, FFST, %BF, and waist circumference) to the intervention. No significant group by time interactions were observed. Body weight, FM, FFST, and %BF increased significantly in both groups over time (i.e., time effects; p < 0.05). Average weight gain was 50–75% less than reported in previous studies of college freshmen. Both soy and milk‐based meal replacements may be beneficial with respect to slowing weight gain in healthy premenopausal women; however, further study is needed to determine the effects of soy and casein meal replacements using a non‐intervention control group. Funded by The University of Georgia Research Foundation.