Soy has recently been tarnished by a variety of mixed messages, which leave people wondering about the validity of its supposed benefits. 
What makes soybeans interesting is that they contain a complex mix of phytochemicals, including isoflavones. Some isoflavones are "phytoestrogens" or plant estrogens, and their possible effect is to mimic the effects of estrogen or act as an anti-estrogen (blocking the effects of estrogens in the body).

Each of soy's professed benefits comes with its own set of debates, leaving researchers stumped and consumers confused:

HEART DISEASE: Soy supposedly reduces the "bad" cholesterol, increases the "good" cholesterol, and is said to provide a small reduction in blood pressure. Even the Food and Drug Administration approved the following dietary health claim for soy foods: "Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease." 

Although some experts claim that the heart healthy benefits are a bit "exaggerated and unrealistic," most researchers agree that there are advantages to eating soy protein to prevent and treat cardiovascular disease -- they just don't concur as to the degree or reason why. Some say it's the isoflavones, others claim it's the unique protein, and there are still others who say it's because soy often replaces other unhealthy foods -- or a combination of all of the above.

"The positive cardiovascular effects of soy are really a package which includes: using soy protein as a replacement for foods that are high in saturated fats and cholesterol; the modest reduction in blood pressure; the small reduction in LDL (bad cholesterol) and increase in HDL (good cholesterol). All this bundled with other positive dietary changes offers enough to make a difference," says David J.A. Jenkins, M.D., Ph.D., D.Sc., a professor in the department of Nutritional Sciences at the University of Toronto.

Bottom Line: "Eating soy protein (not just soy-based products) in moderation and replacing foods that are high in saturated fats can only be positive," says Dr. Jenkins. 

BREAST CANCER: Although there have been a number of clinical trials, there's no definitive answer as to the reduction of breast cancer risk associated with consuming soy. The basis for this claim stems from the fact that women in Asian countries who regularly consume a minimum of 11 grams of soy per day had a lower incidence of breast cancer. Note that much of the positive research shows that soy protein is particularly helpful if consumed during adolescence for the prevention of breast cancer.

Recent news about estrogen brings forth another issue for women and soy intake: If soy mimics estrogen, and estrogen is related to increased breast cancer risk -- then couldn't soy actually cause breast cancer instead of protecting against it? "This is a very valid concern, but it is specific to women who already have estrogen-receptor-positive breast cancer. The research is pretty clear that there is no effect [for the average person], and soy should not be removed from a person's diet," says soy researcher Mark Messina, Ph.D. Also, it should be noted that estrogen is about 1000 times as active as phytoestrogen, and is actually a different substance.

Bottom Line: "It is way too early to draw any conclusions as to whether soy decreases risk (or even increases risk) of breast cancer in women -- with all the studies completed, there is still no conclusion," says Christopher D. Gardner, Ph.D., a professor at Stanford Center for Research in Disease Prevention. 

PROSTATE CANCER: The theory is that soy and isoflavone (specifically genistein and daidzein) consumption reduce the risk of prostate cancer. A recent study in China concluded that soy consumption reduced the risk of prostate cancer among men ages 50-89.

Bottom Line: Although there have been few human studies to date, "there seems to be a real indicator that there is a link to risk reduction," says Dr. Gardner. It couldn't hurt to add a little soy to your diet if you're concerned about prostate cancer.

MENOPAUSAL SYMPTOMS: In theory, it makes sense -- soy protein contains phytoestrogens, which mimic the action of estrogen in some tissues, so it should be able to reduce the problems associated with menopause (reduction of estrogen). Some of the research does show a slight reduction of symptoms in those women who have a high frequency of hot flashes (i.e., five or six per day).

Bottom Line: "Although a great deal of the clinical trials looking at hot flashes and night sweats have shown soy isoflavones fared no better than the placebo, if people believe that it works [placebo effect], then why not?" says Dr. Jenkins.

OSTEOPOROSIS: The theory is that isoflavones, the proteins, or some other components of soy stimulate bone growth, just like natural estrogen. An article in the September 2003 Journal of Clinical Nutrition reviewed all of the latest clinical studies on soy protein and osteoporosis, and concluded that there is evidence that soy protein assists in building stronger bones.

Bottom Line: It is too early to make any firm conclusions, but many researchers are excited about the positive results from early clinical studies.

Although the benefits of soy have been studied, reviewed, and debated among experts, there are still very few definitive conclusions that a consumer can rely on with certainty. However, given that the evidence does point to many positive, albeit unexplained, benefits -- experts recommend integrating a total of 11 grams of soy protein (two eight-ounce glasses of soymilk, or one ounce of Dr. Soy nuts) specifically from food sources -- not supplements -- into your diet throughout each day.

"Soy is among the top in terms of food choices. You still need to have variety in your diet, but if you could only have one spoonful of food for your next meal, and if you hadn't already had soy earlier in the day, you really couldn't do much better in a single spoonful than soy," says Dr. Gardner. 

Other Points to Ponder

SUPPLEMENTS: Much of the research shows that nothing compares to eating actual soy-containing foods. Soy contains a unique and not fully understood combination of nutrients; therefore, it is difficult to extract the exact components that offer the full health effects. "It's easy to overdo it with pills, but you can't really overdo it with food. Until we know what the optimal dose is, we'd prefer to recommend foods (since we do have examples of other nutrients where MORE is harmful, not better)," says Christopher D. Gardner, Ph.D., assistant professor at the Stanford Center for Research in Disease Prevention. In fact, the further away you get from the actual bean, the less effective the isoflavones.

SOY PROTEIN: "For some reason, the amino acid DISTRIBUTION in soy is more similar to human needs than any other plant source of protein. Also, plants often have very little protein compared to animal sources of foods, but soy has a HIGHER PERCENTAGE of protein than any other plant food. For example, many grains contain 10% protein, and most beans contain 20% protein, yet soy has 30-40% protein," says Dr. Gardner.

INFANTS: There were claims that soy could be dangerous to infants because of the high dose of isoflavones being able to duplicate behavior of estrogen. "Recent investigations have compared the millions of children raised on soy infant formula to those who weren't. They looked for changes in the timing or extent of sexual maturation, or other hormone-related possible consequences. The investigators couldn't detect any differences," say Dr. Gardner.

COGNITIVE ABILITY: A study of middle-aged Japanese-American men demonstrated that those who ate at least two servings of tofu per week had a decline in mental ability as they aged, and were more prone to Alzheimer's compared to those who ate no tofu. "No such effects have been seen in Japan, where life expectancy is high and soy protein is a staple -- not only that, elderly Japanese are often regarded as being rather sharp," offers Dr. Jenkins.

NOT CREATED EQUAL: Choose your soy foods wisely since they don't all have the positive benefits. Soy sauce, for instance, contains no soy protein. A recent study showed that isoflavone amounts varied among commercial soy milks and weren't even consistent between repeat purchases of the same product.

WEIGHT GAIN: Even soy foods with a heart-healthy claim on the package may be high in salt, sugar, and calories. Be sure to evaluate food labels carefully. Keep in mind that soybeans contain about 8 grams of fat per serving, which may contribute significantly to your recommended daily fat intake. Oh, and by the way -- when I asked the numerous experts about the effects of soy to help you lose weight -- they made it clear that there was no evidence, other than using it as a lower calorie alternative to other foods.

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