Soy and Isoflavones
Unsafe?... Depends on the Dose
A recent article has people concerned about nutritional supplements containing soy isoflavones. Dr. Steven Clinton from Ohio State University claims that adding soy foods to one's diet is a good way to reduce risk for cardiovascular disease and cancer, but warns that soy supplements, some of which contain extremely high doses of isoflavones such as genistein and daidzin may actually stimulate cancer growth. Really? Aside from assuring that he would make the evening news, Dr. Clinton has very little evidence for his hand-wringing. Exposing immune cells to high concentrations of isoflavones caused a marked alteration of cell function, but it's unscientific and unreasonable to conclude that taking soy supplements causes cancer. On the other hand, you have to admit that there are high-potency isoflavone products on the market and that people often believe that if a little is good, a lot must be better.
What's the best course of action?
Never take your eyes off Mother Nature. In this case, the prudent application of soy research was perfectly clear.
- The Asian diet is believed by most experts to be primarily responsible for their lower incidence of heart disease, prostate and breast cancer.
- Abundant evidence exists to correlate isoflavone intake to reduced risk for these disorders.
Reference: Wiseman H. The therapeutic potential of phytoestrogens.
Expert Opin Investig Drugs. 2000 Aug;9(8):1829-40.
- Based on soy food consumption in Japan, typical daily isoflavone intake has been estimated at approximately 50 mg/person.
Reference: American Journal of Clinical Nutrition 1995; 62:645-9.
- This isoflavone level can be obtained from two and a half servings of soy foods per day; such as 3 cups of soy milk or a cup and a half of tofu.
- Question. Will Americans consume this amount of soy foods every day?
Answer. No way.
- Should Americans eat this amount of soy foods every day?
Answer: Maybe not (see the Soy Debate: Part I)
- So how do we help provide the benefits of soy isoflavones in a safe and efficient way?
Answer: Nature suggests a reasonable dose target for supplementation, being 10 to 50 mg per day. In other words, the amount derived from a natural foods diet rich in soy and other legumes.
- One more point. Some of the high-potency isoflavone products no longer resemble soybeans at all, in that their isoflavone content is skewed by the extraction process. Be sure to select a compound that is carefully extracted to assure that the natural profiles and ratios of isoflavones and other natural compounds are maintained as they are found in the soybean.
IMPORTANT NOTE. This fact sheet refers to features and benefits associated with isoflavones, and controversial points are supported by references to published biomedical literature. Nevertheless, I fully acknowledge that there may be competent scientists who disagree with this position, or who may feel that the cited references provide inadequate scientific support. Such is the case in any rapidly evolving field of research. We encourage readers to consult with their health care professional or scientific expert. We welcome comments from other scientists and look forward to developing consensus on these important issues.