New research clarifies why some people seem to derive a heart-protective benefit from eating soy foods and others don’t.
Japanese men who are able to produce equol—a substance made by some types of “good” gut bacteria when they metabolize isoflavones (micronutrients found in dietary soy)—have lower levels of a risk factor for heart disease than people that can’t produce it, according to a new study in the British Journal of Nutrition.
“Scientists have known for some time that isoflavones protect against the buildup of plaque in arteries, known as atherosclerosis, in monkeys, and are associated with lower rates of heart disease in people in Asian countries,” says senior author Akira Sekikawa, associate professor of epidemiology at the University of Pittsburgh.
“We were surprised when a large trial of isoflavones in the US didn’t show the beneficial effects among people with atherosclerosis in Western countries. Now, we think we know why.”
All monkeys can produce equol, as can 50 to 60 percent of people in Asian countries. However, only 20 to 30 percent of people in Western countries can.
For the study, researchers recruited 272 Japanese men aged 40 to 49 and performed blood tests to find out if they were producing equol. After adjusting for other heart disease risk factors such as high blood pressure, cholesterol, smoking, and obesity, they found that the equol-producers had 90-percent lower odds of coronary artery calcification, a predictor of heart disease, than the equol non-producers.
“I do not recommend that people start taking equol to improve their heart health or for any other reason unless advised by their doctor. Much more study is needed.”
The daily intake of dietary isoflavones—found in traditional soy foods such as tofu, miso, and soymilk—is 25 to 50 milligrams in China and Japan, while it is less than 2 milligrams in Western countries. Equol is available as a supplement—bypassing the need for gut bacteria to produce it—though no clinical trials have been performed to determine a safe dosage for heart protective effects, or if it even does provide such protection.
“I do not recommend that people start taking equol to improve their heart health or for any other reason unless advised by their doctor,” Sekikawa says. “Much more study is needed.”
The researchers are now pursuing funding for a much larger observational study to expand on the findings and eventually a randomized clinical trial to examine the effect of taking equol on various medical conditions and diseases.
“Our discovery about equol may have applications far beyond heart disease,” Sekikawa says. “We know that isoflavones may be associated with protecting against many other medical conditions, including osteoporosis, dementia, menopausal hot flashes, and prostate and breast cancers. Equol may have an even stronger effect on these diseases.”
Additional researchers from the University of Pittsburgh and from Shiga University of Medical Science, Shimane University, and Keio University, all in Japan, are coauthors of the study.
The National Institutes of Health; Japanese Ministry of Education, Culture, Sports, Science and Technology; and a small grant from Pitt Public Health’s department of epidemiology funded the work.
Source: University of Pittsburgh