Isoflavones in plant proteins associated with lower heart disease risk

Consuming plant-based proteins that contain higher amounts of isoflavones may be associated with a moderately lower risk of heart disease, especially for younger women and postmenopausal women not taking hormones, according to new observational research published in the journal Circulation.

Researchers from Harvard Medical School and Brigham and Women's Hospital in Boston, Massachusetts analyzed data from more than 200,000 people who participated in three prospective health and nutrition studies. All participants were free of cancer and heart disease when the studies began.

In the study, researchers analyzed health data of more than 74,000 women from the Nurses' Health Study (NHS) from 1984 to 2012; approximately 94,000 women in the NHSII study between 1991 and 2013; and more than 42,000 men who participated in the Health Professionals Follow-Up Study from 1986 to 2012. All participants were free of cardiovascular disease and cancer at the beginning of each study. Dietary data was updated using patient surveys, conducted every two to four years. Data on heart disease was collected from medical records and other documents, while heart disease fatalities were identified from death certificates.

A total of 8,359 cases of heart disease were identified during 4,826,122 person-years of follow-up, which is the total number of years that study participants were free of heart disease and helps to measure how fast it occurs in a population, the researchers said.

After eliminating several other factors known to increase heart risk, investigators found consuming tofu, which is high in isoflavones, more than once a week was associated with a 18 percent lower risk of heart disease, compared to a 12 percent lower risk for those who ate tofu less than once a month. Additionally, the researchers found favorable association with eating tofu regularly primarily in young women before menopause or postmenopausal women who were not taking hormones.

Qi Sun, MD, ScD, a researcher at Harvard's T.H. Chan School of Public Health in Boston, Massachusetts, said he does not 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, he said.

Sun said populations that traditionally consume isoflavone-rich diets including tofu, such as in China and Japan, have lower heart disease risk compared to populations that follow a largely meat-rich and vegetable-poor diet. However, the potential benefits of tofu and isoflavones as they relate to heart disease needs more research.

Tofu, which is soybean curd, and whole soybeans such as edamame are rich sources of isoflavones. Chickpeas, fava beans, pistachios, peanuts and other fruits and nuts are also high in isoflavones. Soymilk, on the other hand, tends to be highly processed and is often sweetened with sugar, Sun said. This study found no significant association between soymilk consumption and lower heart disease risk.

Sun said the study should be interpreted with caution because their observations found a relationship but did not prove causality. Many other factors can influence the development of heart disease, including physical exercise, family history, and lifestyle habits.

“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,” said Sun in a statement. “Although we have controlled for these factors, caution is recommended when interpreting these results.”