Even though, for example, isoflavone supplementation has proved effective in reducing levels of ‘bad’ LDL cholesterol in many studies, the review, published in the latest edition of the British Journal of Pharmacology, said overall benefits - and risks - required further data.
The major groups of phytoestrogens present in fermented soy products, such as tofu or soy drinks include isoflavones, prenylflavonoids, coumestans, and lignans.
Gut bacteria a factor?
Led by Dr Ivonne Rietjens, from the Wageningen University in The Netherlands, the team undertook an analysis of published literature that spanned the last 60 years.
Potential health benefits of phytoestrogens included lowered risks of cardiovascular disease, obesity, metabolic syndrome and type 2 diabetes, and brain function disorders.
However phytoestrogens are known to interfere in hormone function and the review reflected that with references to infertility and increased cancer risks in oestrogen-sensitive organs such as the breast and uterus.
“This implies that a definite conclusion on the health effects of phytoestrogens, positive or negative, cannot be made," said Rietjens. “It may be that the question of whether phytoestrogens are beneficial or harmful has different answers dependent on individuals' age, health status, and even the presence or absence of specific gut bacteria.”
Go easy with high doses
Professor Mary Ann Lumsden, senior vice president of Strategic Development, Royal College of Obstetricians and Gynaecologists (RCOG) said that it was difficult to draw conclusions from the available literature as some of the studies were small and of variable quality.
“Although there is some evidence of benefit, it is inconsistent; therefore it is not possible to draw definitive conclusions from this study.”
“Information on adverse effects is sparse and since these could be significant, it is difficult to compare risks and benefits at the moment. Further well conducted clinical trials are required.”
Commenting on the review, Professor Edzard Ernst, emeritus professor of Complementary Medicine at the University of Exeter, cautioned moderate phytoestrogen consumption.
“The best advice therefore is to be cautious and avoid the regular intake of phytoestrogens, particularly high dose supplements.”
Source: British Journal of Pharmacology
Published online ahead of print, DOI: 10.1111/bph.13622
“The potential health effects of dietary phytoestrogens.”
Authors: Ivonne Rietjens et al.