Phytoestrogen pills leave menopausal weight untouched, and may add it for some

Phytoestrogen-based products are widely used by menopausal women to ease symptoms, and they are especially popular among women who are also trying to manage their weight. Swapping animal protein for soy protein is a common feature of weight loss regimens, so it matters whether phytoestrogens, the main active constituents of soy foods, actually influence body composition. Despite their popularity, their effect on weight and body fat after menopause has never been clearly established. This review pooled the randomised trial evidence to find out whether the supplements move the numbers women take them hoping to move.

The researchers searched five electronic databases from inception to April 2018, screening 5932 references to identify eligible studies. They included 23 randomised controlled trials with a combined 1880 postmenopausal women, each comparing phytoestrogen supplementation alongside a usual diet against placebo. The outcomes examined covered body weight and the main parameters of body composition: body mass index, waist and hip circumference, total fat mass and percentage of body fat. Subgroup analyses separated healthy women from those with pre-existing metabolic disorders and looked at different types of phytoestrogen.

Overall, phytoestrogen supplementation was not associated with any change in body weight, body mass index, waist or hip circumference, total fat mass or body fat percentage. The only overall shift was a very slight decrease in waist-hip ratio of 0.01. Subgroups told a more textured story: healthy postmenopausal women showed a modest weight decrease of 0.28 kg, and smaller trials showed a 0.49 kg decrease, while women with metabolic disorders such as prediabetes, type 2 diabetes, prehypertension or high cholesterol gained 0.78 kg. There were also indications that daidzein specifically, though not soy products or isoflavone mixes, could produce modest adverse changes in body composition.

This pooling clarifies a muddled literature: whatever phytoestrogens do for menopausal symptoms, the trial evidence gives no support for a meaningful effect on weight or body fat. The split between healthy women, who showed a tiny benefit, and women with metabolic disorders, who gained weight, is the most intriguing result, and the authors flag it as a priority for future research into potential adverse effects. Whether specific compounds like daidzein behave differently from whole soy foods also remains an open question that individual trials were too small to settle.

If phytoestrogen or soy isoflavone supplements are part of your menopause routine, nothing here suggests you need to expect changes to your weight or body composition in either direction if you are metabolically healthy. If you have prediabetes, type 2 diabetes, raised blood pressure or high cholesterol, the association with weight gain is worth knowing about, even though subgroup findings like this are suggestive rather than conclusive. It is mainly a reason to judge these supplements on symptom relief, not on any promise about the scale.