Soy and soy products, which are high in isoflavones, have often been seen as helpful for preventing coronary heart disease (CHD), and in 1999 the U.S. Food and Drug Administration (FDA) approved claims to that effect. But because it can be difficult to isolate the effects of isoflavones from other nutrients, the findings of studies on soy and CHD published have been inconsistent.
That's why dietary guidelines and a science advisory, both published in 2006 by the American Heart Association (AHA), concluded there was little evidence that soy had cardiovascular benefits. Any of the heart benefits gained from eating soy were likely from higher levels of polyunsaturated fats, fiber, vitamins and minerals, and lower levels of saturated fats, rather than isoflavones, the AHA believed.
Recently, however, researchers from China and Harvard University have found more evidence that eating isoflavone-rich tofu, or soybean curd, can reduce the risk of developing CHD.
Eating tofu at least once or more each week reduced the risk of coronary heart disease by 18 percent.
During the study, 8,359 cases of CHD were identified among the nearly 4.9 million person-years of follow-up, or the total number of years participants were free of CHD. The number of person-years of follow-up helps researchers measure how fast something, in this case CHD, occurs in a population.
As tofu consumption went up, CHD risk went down. Eating tofu at least once or more each week reduced the risk of coronary heart disease by 18 percent. Eating tofu less than once a month reduced the risk of CHD by 12 percent.
This association was strongest among young women and postmenopausal women not taking hormone replacement therapy (HRT). The isoflavones in tofu may be especially beneficial in these populations because they mimic estrogens the body makes naturally by binding to estrogen receptors.
Qi Sun, lead author on the study, told TheDoctor that he and his team believe that among postmenopausal women, isoflavones function as estrogens and keep their risk of CHD low. The protective effect of isoflavones may be more pronounced in younger women because their estrogen receptors are more responsive.
The researchers observed what the participants did before they developed CHD, and studied whether what they did was associated with future CHD risk, but other factors may explain why isoflavones lower CHD risk, explained Sun. “…[M]en and women who ate more tofu also exercised more and ate a healthier diet than those who did not.”
Prevention is the cornerstone of public health, and Sun, an assistant professor of nutrition at the Harvard T.H. Chan School of Public Health, went on to say, “Individuals who are at increased risk of developing heart disease should consider switching to healthy, more plant-based diets, of which tofu and other soy products can be really good components.”
The study is published in Circulation.