How Safe Is Soy?

I don't know about you, but for the past year or so I've gotten very confused about the safety of soy.

Both as a food and in supplement form, soy has been sold to women as a miracle food, especially after menopause. It has been found to reduce hot flashes, lower cholesterol and risk of heart disease, prevent breast cancer, relieve vaginal dryness, and strengthen bones. In fact, soy appeared to be so beneficial that last October the Food and Drug Administration (FDA) ruled that food manufacturers could say that soy protein (not its isolated isoflavones that are found in supplements) can help lower cholesterol and protect against heart disease.

But not everything we're hearing about soy is positive. Sixteen years ago, Noni Anderson, a Canadian mother, fed soy milk to her baby girl who had a problem with cow's milk. "She now has all the symptoms of a classic soy baby: menstruated at the age of 10, low thyroid, frequent and intense migraines, learning disabilities, and a skin disease that has been associated with low thyroid called vitilago," Anderson says. While she doesn't blame soy for all her daughter's problems, she does wonder why there was no hint of a possible problem that could come from a diet of soy formula.

Noni's story is not an isolated case. Other people have had bad reactions to soy as well. Several studies linking tofu intake to brain aging and atrophy, thyroid problems, and even the growth of breast tissue have sent out signals of alarm. The media, as usual, ran with the scary headlines. After all, it sells newspapers, magazines, and advertising space on radio and TV. But Elizabeth A. Yeatley, PhD, lead nutrition scientist at the FDA's Center for Food Safety and Applied Nutrition (CFSAN) commented that "every dietary health claim that has ever been published has had controversy."

So what's the real story about soy? I decided to talk with some of the experts on the subject and try to understand what people are saying, why they're saying it, and what's behind their statements alleging that soy causes more problems than it solves.

It's truly difficult to get a clear picture since not all the studies cited to back up any particular point are as good as we'd like them to be. In fact, some are seriously flawed. People and organizations with vested interests often heavily influence the slant of articles both pro and con. Meanwhile, some scientists are concerned about soy's safety based on preliminary studies and it will be years before we get more studies to either back up these opinions or refute them.

I'm convinced that some people don't tolerate soy well, but that doesn't mean soy is harmful to everyone. Let's look at just some of the allegations, and take a peek behind them at the "other" side.

Does Tofu Consumption Cause Brain Atrophy?

Lon White, MD, senior neuro-epidemiologist at the Pacific Health Research Institute and Professor at the University of Hawaii School of Nursing, conducted a study in Hawaii that concluded that Japanese men and their wives who ate the most tofu from ages 45-65 had the greatest loss of cognitive function after age 75. In addition, their brains appeared to shrink and atrophy.

But Mark Messina, PhD, Chairman of the Third International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, notes that Alzheimer's disease typically has been found to be more prevalent among Japanese men living in Hawaii than those living in Japan. In fact, that dementia is lower in Asia than in Europe.

The study, from which this extrapolation was taken, wasn't designed to show a relationship between change in brain size and function and its possible cause. Could eating soy be just one factor in a lifestyle that leads to lower cognitive function as Messina asks? Or could the isoflavones in soy have been responsible for the end results?

Other factors may have influenced the outcome of the Hawaiian study as well, such as the aluminum content of tofu. Aluminum is suspected of being implicated in Alzheimer's. William Harris, MD, of Honolulu, had 16 samples of soy products tested for aluminum at the University of Hawaii. Some of the tofu was high in aluminum, and it was found that aluminum content of soy is increased when it is cooked in aluminum pots. We don't know about the aluminum content of the tofu ingested by the people Dr. White found had decreased brain function. We do know that a two-year study of Japanese women living in Seattle did not show an association between tofu intake and cognitive decline.

Vesanto Melina, MS, RD, co-author of Becoming Vegetarian and Becoming Vegan (Book Publishing Co., 1995 and 2000), points out that, "The Hawaii study's research design was seriously flawed in a number of respects, including not quantifying the amounts of soy consumed. It is a single study, is not more widely reflected, and clearly factors other than soy could be responsible for the findings."

I contacted Dr. White, who replied that only one other study had ever investigated this question, and it was a poor study. His, he claimed, is about as good a study as it gets so far. "But it is still an observational study," he said, adding, "Bottom line is that we have too little information to attach significant importance to such comparisons beyond just saying they are interesting."

Is Soy Bad for Your Thyroid?

As far back as the 1930s, studies have suggested that soy produced goiters in laboratory animals. A goiter is an enlargement of the thyroid caused by an iodine deficiency or hypothyroidism (low thyroid function). A small number of babies who were fed soy formulas without added iodine also developed goiters. Today's formulas contain iodine, which appear to have eliminated the problem. In addition, when soy is heated, the properties that lead to goiters are reduced. Dr. Messina points out that no studies have been designed to study the effects of soy formula on thyroid function.

Researchers at the National Center for Toxicology Research (NCTR), looking at laboratory (not human or animal) studies, proposed that isoflavones and other flavonoids may lead to goiters. At the same time, they said that this is most likely to occur in people with low iodine intake. It appears that low iodine may be more of a problem than a high soy-diet.

Seafood, seaweed, nutritional yeast, and iodized table salt all contain good amounts of iodine. So do most multivitamin/mineral formulas. Dr. Messina points to recent studies examining the effects of soy on thyroid that have failed to show much of a connection.

What about Noni Anderson's daughter? Was she born with hypothyroidism? Did her soy formula contribute to her problems, or were there other factors involved? There's so much we don't know.

Is Soy Harmful for Women With Breast Cancer?

Soy contains phytoestrogens, plant-based chemicals with a weak estrogenic effect, called isoflavones. One of the isoflavones in soy, genistein, has been found in studies to slightly stimulate estrogen-receptor-positive breast cells. But higher amounts of genistein inhibit both estrogen-receptor-positive and estrogen-receptor-negative cell growth. Let's complicate this by pointing out that these studies were done in vitro (in laboratories) not in vivo (in humans). Animal studies, which are better than in vitro studies, show soy actually inhibits chemically induced tumors. And there are no studies I've found that show soy foods increase the risk for breast cancer. Everything I've seen indicates the opposite is true.

The American Dietetic Association has suggested that women who are taking tamoxifen to prevent a recurrence of breast cancer avoid soy. But Dr. Messina reports an animal study that found the combination of miso with tamoxifen inhibited the development of chemically induced breast tumors by 50 percent. Tamoxifen alone had no inhibitory effect. While some oncologists actually use high amounts of isoflavones to help shrink breast cancer tumors, it might be wise, if you've had breast cancer, to avoid soy isoflavones in supplement form unless your doctor says otherwise.

Other Studies/Other Allegations

There are other allegations that suggest soy may be harmful, but I think it's important not to jump to this conclusion yet. Until we have more long-range, double-blind, placebo-controlled studies or other well-designed studies with a large number of participants, we won't know the whole picture. This research is many years away from being completed. Meanwhile, we need to consider both sides of the soy picture -- the positive and the negative.

It's important to realize that not all foods are good or safe for everyone, and too much of a good thing may turn it into a harmful substance. A diet heavily weighted in soy will undoubtedly lead to negative side effects in some people, although the same amount may be safe for someone else. Health writer Bill Sardi points out that the companies growing and distributing soybeans are overpromoting this food. Clearly, there are other forms of protein than soy, even in vegetarian diets.

Some of the negative allegations about soy have come from two scientists at the Food and Drug Administration (FDA). The FDA responded by saying that the benefits of soy outweigh any potential problems, and that soy contains healthy substances and is safe to consume. More information can be found at www.fda.gov.

How Much Soy Is Safe?

Last October, the FDA announced that 25 grams of soy protein a day, along with a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. In Becoming Vegan, Vesanto Melina, RD, points out that one cup of cooked soybeans (like edamame) contains 28 1/2 grams of protein, while half a cup of tofu has 17-20 grams. One veggie burger or soy hot dog has 9-13 grams of protein.

How much do some soy experts eat?

James W. Anderson, MD, does soy research on people at the University of Kentucky. He believes that soy is more beneficial to our health than any other food we could eat. He eats two or more servings of soy a day, beginning with 20-25 grams of soy protein for breakfast.

He also eats soybean chili, soy nut snacks, and includes tofu in stir-fry twice a week.

Mark Messina, PhD, has about 10 servings of soy a week, and estimates he's eating from 10-40 mg a day.

As for me, I add one scoop of soy protein powder to my non-soy cereal in the morning. That's about 12 grams of soy protein. Then I choose from edamame, tofu, and an occasional veggie burger or soy dog for another meal on most days. I do eat many other legumes, as well, and that's what I recommend you do, too.

My Personal Recommendations:

* Everyone is different. Soy may be fine for you, but not for someone else.

* Don't overdo soy or any other "miracle" food or supplement. More of something good isn't always better. One or two servings a day appear to be safe for most people.

* Use the most natural form of soy you can find. Boiled green soybeans (edamame) are less processed than tofu. Tofu and tempeh are less processed than soy dogs, soy burgers, soy cheese, and soy protein powder.

* Use isoflavone supplements judiciously and let your health practitioner know what you're taking in case he or she feels you should be monitored for any possible estrogenic side effects.

* Add other legumes to your diet both for variety in taste and ingredients. People who emphasize soy frequently de-emphasize lentils and other legumes.

Messina, Mark, PhD. "The Soy Connection," J Am Diet Assoc, 2000.

White, L.R., H. Petrovitch, G.W. Ross, K. Masaki, J. Hardman, J. Nelson, D. Davis, and W. Markesbery. "Brain aging and midlife tofu consumption." J Am Coll Nutr, 19: 242-255, 2000.

Rice, M.M., A.B. Graves, S.M. McCurry, L. Gibbons, J. Bowen, W. McCormick, and E.B. Larson. "Tofu consumption and cognition in older Japanese American men and women." J Nutr 130: 676S, 2000.

Divi, R.L. and D.R. Doerge. "Inhibition of thyroid peroxidase by dietary flavonoids." Chem Res Toxicol, 1996 January/February, 9(1):16-23.

Zhou, J.R., E.T Gugger, T. Tanaka, Y. Guo, G.L. Blackburn, and S.K. Clinton. "Soybean phytochemicals inhibit the growth of transplantable human prostate carcinoma and tumor angiogenesis in mice." J Nutr, 1999 September, 129(9):1628-35.

"What about soy?" FDA Consumer, May-June 2000.

Sardi, Bill. "They're taking the joy out of soy," The Townsend Letter for Doctors & Patients, October 2000.