Eating tofu and foods that contain higher amounts of isoflavones was associated with a moderately lower risk of heart disease, especially for younger women and postmenopausal women not taking hormones, according to new observational research.

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

“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,"

said lead study author Qi Sun, M.D., Sc.D., a researcher at Harvard’s T.H. Chan School of Public Health in Boston.

Lower Risk Of Heart Disease

After eliminating a number of 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% lower risk of heart disease, compared to a 12% lower risk for those who ate tofu less than once a month; and

  • The favorable association with eating tofu regularly was found primarily in young women before menopause or postmenopausal women who were not taking hormones.

Sun noted that 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.

Foods High In Isoflavones

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 noted. This study found no significant association between soymilk consumption and lower heart disease risk.

“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,"

Dr. Sun said.

Isoflavones are substituted derivatives of isoflavone, a type of naturally occurring isoflavonoids, many of which act as phytoestrogens in mammals. Isoflavones are produced almost exclusively by the members of the bean family, Fabaceae (Leguminosae).

Causality Not Shown

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.

Sun emphasized that 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 a person’s lifestyle habits.

“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,"

said Sun.

Other Evidence

In 2000, the U.S. Food and Drug Administration approved health claims that soy edibles protect against cardiovascular disease. However, since then, clinical trials and epidemiological studies have been inconclusive, and the agency is reconsidering its now twenty-year-old decision.

The American Heart Association’s 2006 Diet and Lifestyle Recommendations and a 2006 science advisory on soy protein, isoflavones and cardiovascular health found minimal evidence that isoflavones convey any cardiovascular benefits and any protections provided by higher soy intake was likely due to higher levels of polyunsaturated fats, fiber, vitamins and minerals, and lower levels of saturated fat.

The consumption of isoflavones-rich food or dietary supplements is under preliminary research for its potential association with lower rates of postmenopausal cancer and osteoporosis in women.[2] Use of soy isoflavone dietary supplements may be associated with reduction of hot flashes in postmenopausal women.[3]

Despite the frequent use of isoflavone supplements, there are insufficient data on safety and adverse effects. Isoflavones have GRAS status in the United States. The European Food Safety Authority has conducted a risk assessment of isoflavone supplements for post-menopausal women and could not identify adverse effects with intakes up to 150 mg/d, although it criticised the lack of data.

The study was funded by the US National Institutes of Health.

[1] Le Ma, Gang Liu, Ming Ding, Geng Zong, Frank B. Hu, Walter C. Willett, Eric B. Rimm, JoAnn E. Manson, and Qi Sun. Isoflavone Intake and the Risk of Coronary Heart Disease in US Men and Women: Results From 3 Prospective Cohort Studies. Circulation. 2020;141:00–00. DOI: 10.1161/CIRCULATIONAHA.119.041306

[2] Wei, P; Liu, M; Chen, Y; Chen, D. C. (2012). Systematic review of soy isoflavone supplements on osteoporosis in women. Asian Pacific Journal of Tropical Medicine. 5 (3): 243–8. doi:10.1016/S1995-7645(12)60033-9

[3] Soy isoflavones. Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis. 2016.

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