Researchers from the Harvard Medical School and Brigham and Women's Hospital working in collaboration have found that tofu and other plant-based proteins contain certain nutrients called isoflavones that can help those with heart disease and lower their disease risk.
Their study titled, "Isoflavone Intake and the Risk of Coronary Heart Disease in U.S. Men and Women Results From 3 Prospective Cohort Studies," was published in the latest issue of the journal Circulation from the American Heart Association.
What was the study about?
A large population around the world consumes plant-based proteins as their sole source of protein (vegetarians or vegans) or as supplements to animal proteins. Tofu and other plant proteins contain higher quantities of isoflavones. These nutrients lower the risk of heart disease among postmenopausal women who are not on hormonal therapy as well as young women. The purpose of this study was to see if there were any health benefits from soy products related to coronary heart disease (CHD).
The team wrote that the U.S. Food and Drug Administration had first approved a claim in 1999 saying soy products were good for the heart and protected against CHD. Since then, several studies have proven otherwise, and the organization has reconsidered the claims of the heart health benefits of soy products. The American Heart Association, too, in recent guidelines said that the claims of benefits from isoflavones in soy products are minimal, and the actual benefits are due to "higher contents of polyunsaturated fats, fiber, vitamins, and minerals and lower contents of saturated fat."
The researchers also explain that there is a connection between isoflavones and estrogens. Since isoflavones are similar in structure to estrogen, they can bind to the estrogen receptors and exert estrogenic effects.
Tofu is a curd made of soybean. Both whole soybeans, as well as edamame, contain high amounts of isoflavones, the team wrote. Other sources of isoflavones include fava beans, chickpeas, peanuts, pistachios, fruits, and nuts, etc.
What was done?
For this study, 74,241 women enrolled in the NHS (Nurses' Health Study; 1984–2012) and 94,233 women enrolled in the NHSII (Nurses' Health Study II; 1991–2013), and 42,226 men enrolled in the Health Professionals Follow-Up Study (1986–2012) were included. These participants were all free of cancer and heart disease at the start of the study. Every two to four years, the details of their dietary intake were assessed and collected using questionnaires. During follow up deaths due to CHD and heart attacks that were nonfatal were recorded from the medical records and death certificates.
What was found?
Throughout follow up, there were a total of 8,359 cases of coronary heart disease in the total 4,826,122 person-years of follow-up. Results revealed that those consuming tofu high in isoflavones more than once in a week had an 18 percent lower risk of heart disease compared to a 12 percent lower risk of heart disease among those who ate tofu less than once per month. The benefits were more prominent among younger women and postmenopausal women who were not taking any hormone therapy.
Study leader, Qi Sun, M.D., Sc.D., a researcher at Harvard's T.H. Chan School of Public Health in Boston, said, "Despite these findings, I don't think tofu is by any means a magic bullet. Overall diet quality is still critical to consider, and tofu can be a very healthy component." Sun explained that people who consumed more tofu and diets rich in isoflavones, including those in China and Japan, had a reduced risk of heart disease compared to people who consume fewer vegetables and more meat.
Sun added that similar benefits were not seen with soymilk consumption. He said, "Other human trials and animal studies of isoflavones, tofu, and cardiovascular risk markers have also indicated positive effects, so people with an elevated risk of developing heart disease should evaluate their diets. If their diet is packed with unhealthy foods, such as red meat, sugary beverages and refined carbohydrates, they should switch to healthier alternatives. Tofu and other isoflavone-rich, plant-based foods are excellent protein sources and alternatives to animal proteins."
Implications and future directions
The authors of the study concluded, "Higher intake of isoflavones and tofu was associated with a moderately lower risk of developing CHD, and in women, the favorable association of tofu were more pronounced in young women or postmenopausal women without hormone use."
According to Sun, the results are not cause and effect and should be interpreted carefully. He explained that several factors could influence heart disease risk, including lifestyle behaviors such as smoking, physical exercise, family history, etc. He said, "For example, younger women who are more physically active and get more exercise tend to follow healthier, plant-based diets that may include more isoflavone-rich foods like tofu. Although we have controlled for these factors, caution is recommended when interpreting these results." The team wrote, "While these associations warrant replications in other populations, as well as in intervention studies on CVD risk factors, the present study overall implied that tofu and other soy products could be incorporated into overall healthy plant-based diets to facilitate the prevention of CHD."
This study was supported by the National Institutes of Health.
Isoflavone Intake and the Risk of Coronary Heart Disease in US Men and Women: Results From 3 Prospective Cohort Studies Le Ma , Gang Liu , Ming Ding , Geng Zong , Frank B. Hu , Walter C. Willett , Eric B. Rimm , JoAnn E. Manson , and Qi Sun, https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.119.041306