- Author: Ann Brody Guy
Soy is now everywhere in the American diet. Tofu has become a more mainstream ingredient, soy milk crowds dairy cases, and soy fillers and additives can be found in processed foods from soups to meat and vegi-burgers to flavorings like cheese powders. The ubiquitous bean’s high levels of estrogen-mimicking compounds, called phytoestrogens, have long been a topic of scientific study and the nation’s ongoing conversation about nutrition and health. Does eating soy impact our sexual development? Harm women’s reproductive health? Minimize the symptoms of menopause? In a confusing matrix of news reports over the past decade, it’s been reported to both encourage some cancers and protect against others.
“Despite great interest in the effects of phytoestrogens on humans and livestock, very little is known about how often estrogenic plants are consumed by our closest-living relatives, so I decided to begin screening the important plant foods of various wild primate species for estrogenic activity,” said Michael Wasserman, a postdoctoral scholar in the Department of Anthropology at McGill University and lead author of the study, who conducted the research while completing his Ph.D. in UC Berkeley’s Department of Environmental Science, Policy, and Management.
Working in lab of Dale Leitman, an adjunct professor in UC Berkeley’s Department of Nutritional Sciences and Toxicology, Wasserman measured the presence of phytoestrogens in the diets of two leaf-eating primate species from Uganda and found that both species routinely consumed estrogenic plants as part of the staple foods in their diets. The red colobus monkey of Kibale National Park consumed more than 10 percent of its diet in estrogenic plants, and in mountain gorilla of Bwindi Impenetrable National Park, studied by his co-author Jessica Rothman, an assistant professor of primate ecology at Hunter College, estrogenic plants comprised nearly 9 percent of the animals’ total diet.
Wasserman is now looking into how these plants affect the red colobus’s endocrine system, which, like ours, regulates many physiological processes and behaviors. He is also measuring the presence of phytoestrogens in the diets of fruit-eating primates, like the chimpanzee, which should yield more information about the relationship between these animals and plants.
As his findings grow, Wasserman hopes the research will shed light on how long humans have been eating estrogenic plant foods over our evolutionary history.
“Throughout most of human history we have lived as hunter-gatherers, consuming large amounts of wild plant foods, especially fruits, and our biology has changed little since these pre-agricultural times,” he said.
By studying chimpanzees, gorillas, and other wild primates that also depend on wild plant foods to meet their nutritional needs, Wasserman hopes to help clarify the importance of dietary niche (fruit- vs. leaf-eater) and phylogeny (ape vs. monkey) to phytoestrogen exposure.
“If it is only the leaf-eaters consuming these plants, then eating foods like soy may be a relatively new trend for us," Wasserman said. "If fruit-eating apes consume estrogenic plants, we have probably been consuming phytoestrogens for millions of years.”
The study is published in the May issue of the American Journal of Physical Anthropology.
- Author: Janet Byron
One dietary component that has received considerable attention for its potential heart-protective effects is soybeans, which contain lean vegetable protein, dietary fiber and antioxidants called isoflavones.
In a recent issue of the University of California’s California Agriculture journal, scientists reviewed research concerning the relationship between soy and heart disease. Several potential mechanisms have been identified for the observed cardioprotective effects of soy, including cholesterol-lowering properties, antioxidant activity and gene regulation.
“Soybeans and foods made from soy are the major source of isoflavones, which serve as antioxidants, scavenging and neutralizing free radicals that might otherwise cause inflammation and increase the risk of heart disease,” wrote Emily R. Cena, senior writer, and Francine M. Steinberg, professor and chair of the UC Davis Department of Nutrition.
Soy acts like compounds similar to the hormone estrogen, such as blood vessel dilation and gene regulation. “Some health concerns have been raised related to soy's estrogenlike properties, particularly with regard to breast cancer risk, but these concerns were beyond the scope of the current article,” the authors wrote.
The preponderance of research shows that soy isoflavones increase levels of cardioprotective HDL (“good”) cholesterol and decrease levels of LDL (“bad”) cholesterol, thereby lowering the risk of heart disease. Soy may also help ameliorate metabolic syndrome, a constellation of risk factors including abdominal obesity, high blood pressure, insulin resistance and alterations in blood lipids that result in increased risk of heart disease and type 2 diabetes.
A current research project funded by the UC Davis Center for Health and Nutrition Research is investigating the effects of consuming whole soy foods on biomarkers of cardiovascular risk in individuals with metabolic syndrome; it may be completed in 2012.
“Soy isoflavones have a broad variety of biological actions,” Cena and Steinberg wrote. “The beneficial effects of soy are modest compared to pharmacological treatment, such as statin drugs. However, the cumulative effects over a lifetime are likely to be significant.”
The authors highlight epidemiological studies suggesting that Asian populations consuming large amounts of soy have lower rates of cardiovascular disease than Western populations. For example, in the mid-1990s a meta-analysis of 29 clinical trials found that compared to animal protein, soy protein significantly reduced blood levels of several fats (total cholesterol, LDL cholesterol and triglycerides). This prompted the U.S. Food and Drug Administration to approve the current health claim that 25 grams of soy protein per day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.
The review article on soy and heart health was featured in a special issue of California Agriculture journal, “Food as medicine: Can what we eat help cure what ails us?”