Summing up soy studies
Researchers used meta-analysis to combine data from 16 previous clinical trials to study the effects of soy isoflavone supplements on body weight and glucose regulation (how the body metabolizes food to create the blood sugar that fuels cells). All of the study participants were postmenopausal women, and data from these 16 trials were combined to study the effects of soy isoflavones on
- body weight in 528 women,
- fasting glucose (blood sugar) levels in 1,182 women, and
- fasting insulin levels in 1,142 women.
The study revealed significant reductions in body weight, fasting glucose, and fasting insulin levels in women taking isoflavone supplements compared with women in the placebo (no supplement) groups. Lower doses of isoflavones appeared to reduce body weight and blood glucose levels the most, and isoflavones reduced body weight and insulin levels more effectively in normal-weight women compared with obese women.
Though a healthier body weight and better glucose regulation are associated with reduced heart disease risk, it is important to note that the changes were small. The average weight loss in the isoflavone groups amounted to around one pound, and blood glucose levels decreased an average of only 0.2 mg/dL
Smart soy choices
The researchers noted that well-designed clinical trials are needed to further clarify what dose of isoflavones, taken over what duration of time, is most effective for people with different heart disease and diabetes risk factors. Still, this study supports that for some people, isoflavone supplements may provide modest heart disease risk-reduction benefits. Before adding isoflavones into your self-care plan, consider:
- Who was studied? The studies all focused on postmenopausal women. The results do not tell us whether these supplements will have similar effects in men or premenopausal women.
- What's the right dose? With supplements, more is not always better. In this study, lower doses appeared to be more effective than higher doses, the low dose ranging from 40 to 100 mg of isoflavones per day, the high dose defined as above 100 mg per day.
- What are the downsides? Soy isoflavones are safe for many people, but Dr. Alan Gaby, Medical Editor for Aisle7 notes, "There may be some people, such as those who have hypothyroidism or are at risk of developing hypothyroidism, who may need to avoid these products." Consult with your healthcare provider on the best supplement options before making any changes to your self-care practice, especially if you are already managing a health condition.
- Should you try food first? The study found that lower doses of soy nutrients were more effective. Firm tofu provides around 30 mg of isoflavones per 3-ounce serving, while 3 ounces of tempeh provides approximately 35 to 40 mg. Edamame provides between 20 and 50 mg of isoflavones per 3 ounces and soy milk will give you about 25 mg per 8-ounce serving. With just one to 2 servings per day, you can naturally bring your isoflavone intake into the 40 to 100 mg range that the study found most effective.
(In press: Nutr 2012, doi:10.1016/j.nut.2012.03.019; USDA Database for the Isoflavone Content of Selected Foods, Release 2.0; September 2008. Available: www.ars.usda.gov/services/docs.htm?docid=6382)