Overwhelming research points to soy's health benefits Soyfoods have been touted as the silver bullet cure for a myriad of health problems. Study after study alleges that soy can shoot down heart disease, cancer, osteoporosis and even postmenopausal symptoms. But just how much of the hype is true? Fact is, questions have been raised that place a shadow on soy's health benefits.
In February 1999, two FDA scientists, Daniel Sheehan and Daniel Doerge, protested the impending approval of the health claim for soy protein. They stated, "It is unreasonable to approve the health claim until complete safety studies of soy protein are conducted."
Most of the safety concerns pertain to soy's possible negative impact on the thyroid gland, and on the health of babies consuming soy-based infant formula. In both cases, research has shown no negative effects. However, there have been personal reports of a relationship between overconsumption of soy and hypothyroidism and goiters.
In addition, New Zealand, Australia and Great Britain all have voiced concern about the safety of soy-based infant formula, and have looked at limiting its use.
Despite these concerns, FDA officials approved the soy protein health claim in October 1999. It states: "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease."
Studies reviewed by FDA proved up to a 15% decrease in cholesterol rating and a 30% reduction in the risk of a heart attack.
"I think there was more than sufficient evidence ... to show that soy protein can, in a healthy diet, bring down moderately to high cholesterol levels," says Anne Patterson, a registered dietician from Nutrition Advantage, Farmington, IL.
James Anderson, professor of medicine and clinical nutrition at the University of Kentucky who analyzed the results of 38 experiments, agrees. "Soy is like a designer food for blood fats," he says. "It does all the things we want it to do."
BENEFICIAL COMPOUNDS Studies have yet to prove what chemical in soy is beneficial or how much we should consume, but two compounds, genistien and daidzein, get credit for the positive effects. Those two compounds, also called isoflavones, are phytoestrogens, or plant-derived estrogens.
However, more and more research points to possible health benefits from saponin, another compound found in soy.
"When you eat soy, it's not just isoflavones that are in there," says Mark Berhow, a USDA researcher. "There are hundreds of thousands of different chemical species that make up a soybean. It could be any combination of those compounds that give us the effects we're seeing."
A FIGHTING FORCE Soy shows promise in fighting several health problems facing Americans. Here's what's known so far:
- Osteoporosis. Estrogen has long been heralded in keeping bone loss from occurring in post-menopausal women. Soy's phytoestrogens are showing similar effects and may actually help women increase bone mass, not just prevent bone loss.
- Menopause. Many postmenopausal women hope that there is an alternative to the standard hormone replacement therapy (HRT). The estrogen found in standard HRT is taken from a compound in horse urine. Postmenopausal women taking HRT cut their heart disease risk by 50% and hot flashes by 70%.
While a Mayo Clinic study revealed some evidence that soy reduces the incidence of hot flashes, a new study presented to the American Heart Association shows that soy may decrease the severity of hot flashes, not the number.
- Cognitive Function. Animal research supports scientists' theory that phytoestrogens protect brain function just as estrogen does. A study of 727 women documenting estrogen's effect on cognition in HRT proved women who took estrogen scored higher on cognition tests than those who didn't.
A Hawaiian study of Japanese-born Americans linked tofu consumption to Alzheimer's. But the study has been widely criticized for lack of scientific protocols.
- Cancer. Soy's phytoestrogens may vie with naturally occurring estrogens within the body, blocking some stronger estrogens. This has been linked to many types of cancer prevention, including breast, bowel and prostate cancers.
"Genistien is mutagenic, but on the other hand genistien may be the perfect thing to fight existing cancer cells because it slows or stops the growth of rapidly dividing cells," says USDA's Berhow. "It may not be good for preventing cancer, but it might be good for treating it."
Although American women are four times more likely to develop breast cancer than their Japanese counterparts who consume more soy, the scientific data on the effect of soy on estrogen-receptor cancers is unclear. The best advice is still to ask your doctor.
"People need to visit with their primary health care provider. There is no silver bullet that takes care of every difficulty that we have," says Tony Anderson, president of the American Soybean Association. "You want to be accurate about monitoring what you're taking, why you think you're taking it and what is happening to you as you do it," he says.
Experts claim more research is needed to gain definitive answers on some health issues. Soy may not prove to be the silver bullet, but scientists say its possible wide- reaching effects on health are encouraging.
Two things may explain conflicting research results about the effects of soy and isoflavones on human health. Both boil down to a lack of clear scientific protocols.
1) Soy or soy-derived compounds vary from study to study. Some studies use tofu, some use soy meal or soy flour, others use a pill form of isoflavone. Even FDA scientists aren't sure what compound in soy makes it work.
"We don't know whether it's the protein or the isoflavones that are having the predominant effect," says James Anderson, a professor of medicine and clinical nutrition at the University of Kentucky. "Isoflavone supplements don't lower cholesterol and we have some studies that show soy protein by itself is not very effective. It looks like it takes the combination of the protein and the isoflavones to get the optimal effect."
2) Scientists aren't sure what dose to give, when to give it, and whom to give it to. Even though isoflavone supplements are now prevalent on the market, Mark Berhow, a USDA researcher, says they usually contain far more isoflavones (200+ mg/pill) than the actual soybean. Soybeans contain 2-4 mg of isoflavone per gram of protein.
How do you make sure you're not overconsuming soy? Eat whole foods - not supplements - and read labels, experts say.
"The whole food is always going to provide a much better balance for people than taking something in a highly concentrated pill or powder form," says Mary Shomon, founder/editor of thyroid-info.com and author of Living Well with Hypothyroidism.