“Soy may be a suitable food for anti-obesity efforts because of its high protein and isoflavone content,” according to a new study, written by Masoumeh Akhlaghi, Morteza Zare and Fatemeh Nouripour in the international review journal Advances in Nutrition.
“Soy showed no overall statistically significant effect on weight, waist circumference, or fat mass, but a significant increasing effect on weight was observed in some circumstances: for instance, in obese subjects [mean difference (MD): 0.80 kg; 95% CI: 0.15, 1.45 kg; P = 0.02], with ingestions of ≥40 g soy protein/d (MD: 0.94 kg; 95% CI: 0.11, 1.77 kg; P = 0.03), with short-term applications (1–3 months) (MD: 0.45 kg; 95% CI: 0.05, 0.86 kg; P = 0.03), and when soy was compared with meat (MD: 0.36 kg; 95% CI: 0.09, 0.64 kg; P = 0.03) and whey protein (MD: 1.53 kg; 95% CI: 0.10, 2.96 kg; P = 0.04).
“In contrast to the effects of soy on weight, soy significantly decreased waist circumference in older ages (MD: −0.36 cm; 95% CI: −0.71, −0.01 cm; P = 0.04), in women (MD: −0.32 cm; 95% CI: −0.57, −0.08 cm; P = 0.01), and at doses of <40 g soy protein/d (MD: −0.31 cm; 95% CI: −0.57, −0.05 cm; P = 0.02).”
Isoflavone studies, which were conducted only in women, showed that isoflavones may reduce body mass index (MD: −0.26; 95% CI: −0.55, 0.04; P = 0.085). The results were most marked in in dosages of less than 100 mg per day (MD: −0.48; 95% CI: −0.90, −0.06; P = 0.02) and in intervention periods of 2–6 months (MD: −0.28; 95% CI: −0.56, 0.00; P = 0.053). However, no effect was observed in higher doses or longer intervention periods, the researchers noted.
“Overall, results showed that, although soy is the major source of isoflavones, soy and isoflavones may have different impacts on weight status,” the study also noted.
The research was based on a meta-analysis to evaluate potential effects of soy and soy isoflavones on weight, waist circumference, and fat mass. PubMed, MEDLINE, Scopus, EMBASE, and Cochrane databases were searched and 24 trials with soy and 17 trials with isoflavones were included in the analysis.
Isoflavones and health: Conflicting messages
A key distinction between soy and other legumes is its high isoflavone content.
Previous research has linked isoflavones to a number of health benefits, ranging from blood cholesterol reduction to osteoporosis prevention and the easing of menopausal symptoms.
However, isoflavones can also bind to oestrogen receptors in the body, leading the molecules to be classified as phytoestrogens. This has given rise to concerns that isoflavones could have undesirable side effects, an issue that has helped give rise to the popularity of ‘soy free’ claims.
Source: Advances in Nutrition
"Effect of Soy and Soy Isoflavones on Obesity-Related Anthropometric Measures: A Systematic Review and Meta-analysis of Randomized Controlled Clinical Trials"
vol. 8: 705-717, 2017; doi: 10.3945/ an.117.015370
Authors: Masoumeh Akhlaghi, Morteza Zare and Fatemeh Nouripour