Phytoestrogen supplementation in addition to usual diet appears to have little impact on body composition in postmenopausal women.
A systematic review and meta-analysis of 23 randomised controlled trials found phytoestrogen supplementation had no effect on body weight, BMI, waist circumference, hip circumference, total fat mass or percentage body fat.
The 1,880 women in the trials were four to 16 years into menopause and were not using hormone replacement therapy.
Supplementation compared to placebo did lead to a small decrease in waist-to-hip ratio in the eight studies that included that data, the study found.
In a sub-group analysis based on the health of the women, the study found phytoestrogen supplementation lead to a small weight loss (0.28kg) in healthy postmenopausal women.
However in women with evidence of metabolic disorders such as prediabetes, type 2 diabetes, prehypertension or hyperlipidaemia, supplementation, compared to placebo, increased their body weight.
Women were also more likely to lose weight if they were supplemented with an isoflavone mix and more likely to put on weight with daidzein.
The researchers said while many obese women tried phytoestrogens for the relief of menopausal symptoms, the mechanism by which they may reduce adiposity was not fully understood.
“Phytoestrogens may affect the body composition directly binding oestrogen receptors (mainly ER α), by mediating the action of hormones thought to be involved in the regulation of body composition (adiponectin, ghrelin, insulin, leptin) or by altering the metabolic activity of adipocytes,” they said.
They concluded the type of phytoestrogens and underlying disease in women may modify the effectiveness of phytoestrogens in improving body composition and may even lead to increase in body weight.
“Therefore, until obtaining more evidence in favor of beneficial role of phytoestrogens in reducing body weight, it might be much safer to combine phytoestrogen supplements (especially daidzein rich formulations) with hypocaloric diet/enhanced physical activity to maintain normal body weight during the supplementation period.”