The article, published in the journal Nutrients, looks at studies conducted on soy including those reported in 2016. The article reviews studies on the food’s effect on a number of health parameters, including cardiovascular disease, bone health, kidney function, breast cancer, prostate cancer, cognitive function and thyroid function.
One of the key differences between soy and other legumes is the bean’s high isoflavone content. Isoflavones are one of the sources of soy’s purported health benefits, but they can also bind to estrogen receptors in the body in a way similar to how the hormone itself behaves, leading the molecules to be classified as phytoestrogens. This property has given rise to concerns that the molecules could have untoward effects. The issue has dogged soy foods for years, and has helped drive the popularity of ‘soy free’ claims and has even led some less scrupulous marketers to speak of the ‘dangers’ of soy when hawking their alternative products.
The article’s author, Mark Messina, PhD (full disclosure: While Messina an adjunct professor at Loma Linda University he is also was director of the industry-funded body the Soy Food Institute), acknowledges the issue but said that recent developments are finally burying that particular hatchet. Much of the concern about estrogenic effects comes from mice and rat studies, Messina said, which in this regard are of limited value because those animals metabolize isoflavones differently than do humans. This fact has now been officially recognized via an opinion issued a little more than a year ago by EFSA.
“Although isoflavones are purported to exert a number of health benefits these molecules are not without controversy. Concerns have arisen that because of their estrogen-like properties they may exert untoward effects in some individuals such as postmenopausal women. However, after a comprehensive, multi-year evaluation of the literature, the European Food Safety Authority (EFSA) concluded that in postmenopausal women, isoflavones do not adversely affect the three organs that were investigated, the breast, thyroid and uterus,” Messina wrote.
Cardiovascular events continue to be the most common cause of death worldwide, leading to an ongoing search for the best intervention strategies. Messina said that the research on soy shows the food can have significant effects in improving overall cardiovascular health markers. Messina said this could in part be attributed to soy’s balance of fatty acids as well as its overall protein quality.
“Soy protein is higher in quality than other legume proteins and the soybean is a good source of both essential fatty acids. Soy protein also directly lowers circulating LDL-cholesterol levels and may also modestly lower blood pressure. Replacement of commonly-consumed sources of protein in Western diets by soyfoods may also lead to a favorable change in the fatty acid content of the diet,” he wrote.
Promise for isoflavones
Messina said research on some other areas is more preliminary. Isoflavones have been shown to have potential applications in skin health and in alleviating depressive symptoms in some study groups. In these, as in other areas of the purported benefits of isoflavones, more research is necessary, he said.
“The most distinctive aspect of the soybean is its high isoflavone content. Isoflavones are proposed as having a number of health benefits although not surprisingly, the degree to which the evidence supports these claims varies. For example, there is solid evidence in support of isoflavones alleviating hot flashes and improving arterial health in menopausal women whereas the evidence that they reduce risk of breast and prostate cancer, not surprisingly, is more preliminary,” he wrote.
Messina said that there is no recommendation for how much soy people should consume to get these health benefits. And a confounding factor (in a good way) is the notion that soy can substitute for less healthful elements of the diet.
“Population and clinical studies involving adults suggest benefits are associated with approximately two to four servings per day. Ideally, soyfoods are incorporated into the diet by displacing less healthy foods and as part of an overall healthy diet designed to lower risk of chronic disease such as the approach represented by the portfolio diet,” he wrote.
“Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature”
2016, 8(12), 754; doi:10.3390/nu8120754
Author: Messina M