 Soy foods are a mainstay of Asian cuisines. The soybean has been cultivated in China for at least 3000 years and its most popular food varieties – tofu, soymilk and tempeh – have grown increasingly popular in the West in recent years. Soy foods offer an exceptional source of protein, are low in saturated fat (in contrast to the meat and dairy they often replace) and are also a good source of many other nutrients, including iron, calcium, dietary fiber, vitamins B1, B2, B6, E and folic acid.
Since 1995, when three New England Journal of Medicine articles provided landmark research supporting cardiovascular benefits of soy,1-3 including significant decreases in total cholesterol, LDL cholesterol and triglycerides, there has been a groundswell of new research on soy, as well as an Internet-based backlash against the humble bean. Soy has been praised as a miracle food and lambasted as a poison.
EVIDENCE AND CONTEXT
Here at Cleveland Chiropractic College, we strongly believe that when such controversies erupt, the proper response is to examine studies in the peer-reviewed scientific literature, which by now contains a substantial body of evidence evaluating the health effects of soy. But because individual research articles may be flawed or misleading, it is even more important to read research summaries from trustworthy sources that take a broad view of the entire body of research and apply it to day-to-day practice. Students and practitioners need to see the forest as well as the individual trees; they need appropriate context and an appreciation of complexity. In the long run, this is far better than aiming for quick-and-easy, all-or-nothing conclusions. When it comes to human nutrition and to health-related goals in general, attempting to make one single food or nutrient, or any single type of treatment, the be-all and end-all is usually a false path.
A FOOD, NOT A DRUG
When evaluating the helpfulness of any food, it is important to see it first and foremost as one part of the overall diet and not as a silver-bullet answer to the symptoms or signs of a particular disease. That is, it should be seen as a food and not a drug. From this perspective, soy can be appreciated a source of valuable nutrients and a potential replacement for less healthy foods. It should not been viewed as a single-agent cure for high cholesterol, coronary heart disease, prostate cancer, or any of the other health issues to which it has been linked.
CARDIOVASCULAR EFFECTS
Since 1999, the U.S. Food and Drug Administration has permitted foods containing soy protein to advertise their heart-healthy qualities. As noted by the FDA at the time, “This final rule is based on the FDA’s conclusion that foods containing soy protein included in a diet low in saturated fat and cholesterol may reduce the risk of CHD [coronary heart disease] by lowering blood cholesterol levels … Foods that may be eligible for the health claim include soy beverages, tofu, tempeh, soy-based meat alternatives, and possibly some baked goods.”
Foods containing soy qualified (and still qualify) for this nutrition claim because the FDA concluded that sufficient research justified the claim. However, as further research has emerged in the intervening years, the evidence for these specific cardiovascular claims has weakened. In 2006, a panel representing the American Heart Association (AHA) Nutrition Committee published a report4 summarizing new research which concluded that, “isolated soy protein with isoflavones compared with milk or other proteins decreased LDL cholesterol concentrations in most studies; the average effect was approximately 3%. This reduction is very small … no benefit is evident on HDL cholesterol, triglycerides, lipoprotein(a), or blood pressure. Thus, the direct cardiovascular health benefit of soy protein or of isoflavone supplements is minimal at best.” |
