Previous research studies have reported that soy protein shakes, when consumed as part of a weight maintenance plan, can improve body composition by decreasing either total body fat or decreasing belly fat in postmenopausal Caucasian and African-American women. A new obesity research study examined the possible benefits of soy protein on body composition and body weight in postmenopausal Chinese women .
For this new body composition study, postmenopausal Chinese women were asked to maintain their normal diet and physical activity routine and were randomly assigned to consume (1) 15 grams soy protein + 100 mg soy isoflavones (expressed as aglycones), (2) 15 grams milk protein and 100 mg soy isoflavones, or (3) 15 mg milk protein alone daily for 6 months in addition to their normal dietary routine. After 6 months, the study investigators reported mild, but significant benefits of soy protein and isoflavones on body weight, body mass index (BMI), and body fat as outlined below:
- Women consuming soy protein and isoflavones lost about 1.6 pounds more than women consuming milk protein and isoflavones and about 1.3 pounds more than women consuming just the milk protein.
- Similarly, postmenopausal women in the soy protein and isoflavones group lost about 3.74% more body fat than women in the milk protein and isoflavones group and about 2.54% more body fat than women in milk protein alone group.
- When looking at only women who were within 4 years of menopause, consumption of soy protein and isoflavones was more effective at lowering body weight, BMI, waist size, and body fat compared to the other two groups.
This is an interesting study that confirms the benefits of soy protein and soy isoflavone consumption for body composition. Since this was not a weight loss study, it was not surprising to see only modest changes. Additionally, the average BMI of the study volunteers was 24.5, which represents a normal body weight, and 38% of the study volunteers were within their normal body weight range. This suggests that even postmenopausal women who are not overweight might derive some modest, beneficial body composition changes with dietary soy consumption.*
It is interesting to note that the isoflavone group, those receiving milk protein and isoflavones, did not obtain any body weight, BMI, body fat, or other body composition benefits. This suggests that the combination of soy protein and isoflavones likely provides the best dietary approach.
1. Liu Z-m, Ho SC, Chen Y-m, Ho YP. A mild favorable effect of soy protein with isoflavones on body composition – a 6-month double-blind randomized placebo-controlled trial among Chinese postmenopausal women. International Journal of Obesity 2010; 34:309-318.