Got soy? A good food ... but no miracle worker. (Special Feature).
Soy is everywhere. One in four Americans eats a soy food at least once a week, according to a recent industry survey.
"Soy has become the yogurt of the 2000s," says Mark Messina, a soy expert and adjunct professor at Loma Linda University in California.
"In the '70s, yogurt was a healthy food that you only ate if you wanted to live to be 110," Messina explains. "Then it moved into the mainstream. Soy is now ready to follow the same path."
Soy is being touted as an anti-cancer, anti-heart-disease, anti-osteoporosis miracle worker. And with new uncertainties about the safety of hormone replacement therapy (HRT), food companies and dietary-supplement makers are scrambling to promote soy--and the plant estrogens it contains--as a natural alternative to prescription estrogen for women who are searching for something safer.
Does soy really live up to its billing? Here's a rundown of what's currently known.
The promise. Soy can lower cholesterol levels and reduce the risk of heart disease.
The reality. It can ... but you've got to eat a lot.
In the early 1990s, the United Soybean Board, an industry trade group, hired University of Kentucky researcher James Anderson to review the results of 38 well-conducted clinical trials showing that soy lowers blood cholesterol levels.
Anderson's 1995 study started the ball rolling. Four years later, the FDA told manufacturers that their labels could claim that soy can help reduce the risk of heart disease, but with a few stipulations.
The feds decided that 25 grams of soy protein a day could lower the average person's cholesterol by about nine points. (In one study, that translated into a six percent drop in LDL ["bad"] cholesterol.) So the FDA permitted foods that contain a quarter of that amount (6 1/4 grams) per serving to make the claim. Its reasoning: people can eat soy foods four times a day.
But even most Asians don't eat that much, says Mark Messina. To get 25 grams, you'd need the equivalent of some four (eight-ounce) cups of soy milk or 12 ounces of tofu every day.
And the FDA approved a health claim only for soy protein, not for the isoflavones that are found in soy. (Isoflavones are the plant estrogens that are among soy's active ingredients.)
"That was a wise decision, since there isn't much evidence that these isoflavones by themselves lower cholesterol levels," says Mary Anthony of the Wake Forest University School of Medicine in Winston-Salem, North Carolina.
Messina's bottom line: "Though soy has a relatively modest effect on cholesterol levels, I still encourage people who are concerned about heart disease to eat soy foods."
The promise. Soy or its isoflavones can relieve hot flashes, night sweats, and other symptoms of menopause.
The reality. Soy is probably no better than a sugar pill. "Most studies have found that soy has no more effect than a placebo," says Gregory Burke of the Wake Forest University School of Medicine. Burke has led three large studies on menopausal symptoms.
Roughly 5,000 women start menopause each day in the U.S. The most popular supplement for coping with symptoms: soy or the isoflavones extracted from soy.
Soy got a boost last July when researchers abruptly halted the Women's Health Initiative trial, which was testing the combination of estrogen and progestin that millions of women take after they start menopause. The hormones increased (slightly) the risk of invasive breast cancer, heart attacks, strokes, and blood clots, stunning scientists and consumers alike.
Alternatives to estrogen-progestin for menopause are "a hot market," Rieva Lesonsky of Entrepreneur magazine told the Associated Press last August.
"Entrepreneurs are saying, `How can I get my part of this?' There's no question that this is going to be a lucrative market for at least the next 15 to 20 years," she said.
But to make money selling soy for menopause, companies will have to ignore most of the research. Six published or not-yet-published studies in the U.S.--from MIT, Tuft University, the Mayo Clinic, Iowa State University, and Wake Forest University--have come up almost empty.
"We found that soy protein, with or without isoflavones, was no better than milk protein in relieving hot flushes and night sweats," says D. Lee Alekel of Iowa State University. She and her colleagues gave 69 menopausal women soy protein that was rich in isoflavones (80 mg a day), soy protein that was low in isoflavones (4 mg a day), or milk protein as a placebo. (1) "After six months, the frequency of hot flushes and night sweats was the same in all three groups," says Alekel.
Only two U.S. studies have found a slight benefit from soy or soy isoflavones. A study sponsored by Johnson & Johnson, which sells Healthy Woman soy pills, gave 122 women either 50 mg of isoflavones in pills or a placebo every day. After 12 weeks, the isoflavone-takers detected a modest relief in the severity--but not the frequency--of their symptoms. (2)
And in the first of two Wake Forest studies, 51 women who consumed 34 mg a day of isoflavones in a soy beverage also had a small reduction in the severity, but not the frequency, of their hot flashes. (3)
However, soy isoflavones bombed in the second, longer study, in which daily soy drinks with 42 mg or 58 mg of isoflavones were no better than a soy drink with 4 mg at relieving hot flashes and night sweats over a two-year period in close to 250 women.
"The claims about soy isoflavones relieving menopausal symptoms have been blown way out of proportion to what the research shows," concludes Alekel. "The weight of the evidence just doesn't show much of an effect on symptoms."
The promise. Soy or its isoflavones can prevent breast cancer.
The reality. It's too early to say.
"The studies looking at women's soy consumption and their risk of breast cancer are conflicting," says Barbour Warren of Cornell University's Program on Breast Cancer and Environmental Risk Factors. "Only some studies of Asian women have found a link, and other studies have found no association at all," he says.
What has caught researchers' attention are two studies showing that eating soy before or during puberty is linked to a lower risk of breast cancer in women:
* In 2001, Vanderbilt University researchers interviewed 1,500 Chinese women with breast cancer and 1,500 similar women without breast cancer. Those who said they had eaten the most soy between the ages of 13 and 15 had half the risk of those who ate the least soy. (4)
* From 1995 to 1998, Anna Wu of the University of Southern California and her colleagues interviewed 500 Asian-American breast cancer patients and 600 similar women without breast cancer in Los Angeles County.
Those who reported having consumed at least one serving of soy foods a week during adolescence had a significantly lower risk of breast cancer than those who said that they ate little or no soy. (5) Those who ate the most soy during both adolescence and adulthood were protected the most.
"This human research is consistent with what my group has found in a series of animal studies," says Coral Lamartiniere of the University of Alabama at Birmingham.
"If we expose adult female rats to a potent carcinogen, they're protected to some extent from developing breast cancer if they had consumed genistein before puberty or both before puberty and during adulthood," says Lamartiniere. Consuming genistein only during adulthood didn't protect them. (6) (Genistein is one of the two major isoflavones in soy.)
"What soy seems to do during early life," says Lamartiniere, "is stimulate the differentiation of the terminal end buds in the breast."
"Terminal end buds are where cancer typically develops in the adult breast," says Mindy Kurzer of the University of Minnesota. "The more differentiated they are, the less likely they will become cancerous."
"The effect of soy may be comparable to the impact of an early pregnancy, which changes the breasts and makes them less susceptible to cancer," adds Lamartiniere. But soy's window may close after puberty.
What happens when women start consuming soy and its isoflavones as adults? Is it protective ... or might it promote breast cancer, like a woman's own natural estrogen does?
"This isn't entirely clear," says Kurzer.
A few years ago, two small studies sent shock waves through the soy research community. In 1996, researchers at the University of California at San Francisco were surprised to find signs of breast cell proliferation in some premenopausal women who had consumed 38 grams of soy protein a day for six months. (7) Cell proliferation may raise the risk of breast cancer. Postmenopausal women were unaffected.
Then in 1998, researchers in the United Kingdom reported signs of breast cell proliferation in 18 pre-menopausal women after just 14 days of eating rolls containing 60 grams of soy protein and 45 mg of isoflavones. (8)
But the alarm may have been premature. A year later, the UK researchers reported that when they added data from ten more women, the impact of soy on breast cells was no longer statistically significant. (9)
The bottom line: "No one has reliably demonstrated an increased or decreased risk of breast cancer among women eating soy," says Cornell's Warren.
Even so, women who already have breast cancer should err on the side of caution. "We can't rule out the possibility that soy may be the wrong food to eat if you have breast cancer," says Mindy Kurzer.
The promise. Soy or its isoflavones can prevent or treat prostate cancer.
The reality. It's too early to say.
"There's some preliminary epidemiological evidence that men who eat soy foods have a lower risk of developing prostate cancer," says Len Cohen of the American Health Foundation in Valhalla, New York. For example, Japanese men have much lower rates of prostate cancer than U.S. men.
Studies that feed animals the soy isoflavone genistein also seem promising. "We've shown in two models that genistein in the diet protects rats and mice from developing prostate cancer," says Coral Lamartiniere of the University of Alabama at Birmingham.
So far, only two small trials in humans have tested soy or its isoflavones on prostate-specific antigen (PSA) levels. (Many more trials are in the works.)
In the first, PSA levels didn't budge in 34 men in their 60s with elevated PSAs (but cancer-free biopsies) who drank a soy beverage with 69 mg of isoflavones every day for six weeks. (10) (Their PSAs averaged eight. A normal PSA is under four.)
In the second, Omer Kucuk and his colleagues at Wayne State University in Detroit gave 41 men with advanced prostate cancer 200 mg of isoflavones every day for an average of six months.
(No one got a placebo because it would have been unethical to give a dummy pill to men with no other treatment options. That makes the results difficult to interpret.)
"The men's PSA levels continued to rise, but not at the same rate as before," reports Kucuk. "And for 24 of the men, PSAs increased by less than 50 percent, which means that their disease had stabilized." That's significant, Kucuk points out, "because we have no effective treatment left to offer patients like these." Unfortunately, the study wasn't designed to see whether the isoflavone pills prolonged the men's lives.
However, Len Cohen worries about men who take isoflavone pills during the later stages of prostate cancer. His new (not yet-published) study found that isoflavones may stimulate--not slow--the growth of advanced prostate tumors in rats.
"Under the right conditions, soy may be valuable in preventing prostate cancer, but then at other times it could be dangerous," he suggests.
The bottom line: "We don't have enough human studies yet to say whether the isoflavones in soy affect prostate cancer for better or for worse," says Kucuk.
Bones and Osteoporosis
The promise. Soy builds bones.
The reality. It's too early to say.
"There are no good long-term studies comparing a soy-rich diet with a dairy-rich diet for their effects on bone," says Robert Heaney of Creighton University in Omaha, Nebraska.
Contrary to what many people have heard, "the high soy content of the typical Japanese diet does not protect them against osteoporosis," he explains. "In fact, the Japanese have as much or more osteoporosis than Caucasians in the U.S. Their risk of spinal osteoporosis is 40 to 50 percent higher than ours."
So why do the Japanese suffer fewer hip fractures than Caucasian Americans? "It's probably because of genetic differences in the way their hips are shaped," says Heaney.
Meanwhile, some researchers are testing whether the isoflavones in soy stimulate bone growth like natural estrogen does.
"Studies looking for an effect of soy or its isoflavones on bone density have found either nothing or a very modest impact," says Gregory Burke of Wake Forest University.
"We don't know yet if soy isoflavones are beneficial for bone because many of these studies have been for short periods of time or involved small numbers of volunteers," says William Wong of the Baylor College of Medicine in Houston. "That's why the government is funding two large long-term trials to find out."
Wong and his colleagues will give 400 postmenopausal women a pill containing 80 mg or 120 mg of soy isoflavones or a placebo every day for two years and monitor how it affects their bone mineral density. (That's the amount of isoflavones you'd get in three to five cups of soy milk or two-thirds to one pound of tofu.)
"We're going to try to answer the three questions everyone wants answered," says Wang. "Do soy isoflavones work? Are they safe? And, if they do work, how much should you take?"
Meanwhile, D. Lee Alekel of Iowa State University and her coworkers will give 234 postmenopausal women 80 mg or 120 mg of soy isoflavones or a placebo every day for three years while monitoring the mineral density in their lower spines.
The bottom line: Until more studies report in, the impact of soy or its isoflavones on bones is far from clear.
(1) Menopause 8: 17, 2001.
(2) Menopause 7: 236, 2000.
(3) Menopause 6: 7, 1999.
(4) Cancer Epidemiol. Biomarkers Prev. 10: 483, 2001.
(5) Carcinogenesis 23: 1491, 2002.
(6) Journal of Nutrition 132: 552S, 2002.
(7) Cancer Epidemiol. Biomarkers Prev. 5: 785, 1996.
(8) Amer. J. Clin. Nutr. 68(suppl): 1431S, 1998.
(9) J. Clin. Endocrin. Metab. 84: 4017, 1999.
(10) Journal of Urology 165: 294, 2001.
RELATED ARTICLE: Straight isoflavones?
Want your isoflavones straight? Supplement manufacturers are eager to oblige. You can find pills that contain anywhere from 3 mg to 80 mg of isoflavones that have been extracted from soy or other plants. You'd have to eat about 11 ounces of tofu to get 80 mg of isoflavones. Even so, you might want to think twice before you swallow the pills.
First, the evidence is slim that isoflavones, by themselves, have the benefits that some people hope soy does.
"Soy with its isoflavones intact lowers blood cholesterol levels, but the isoflavones extracted from soy don't," says Mary Anthony of the Wake Forest University School of Medicine. "Even when we then add back the isoflavones to the soy, it still isn't as good as the original soy was at lowering cholesterol."
"I think it's foolish to say that these isolated isoflavones have beneficial effects, because we really don't know if they do," says Iowa State's D. Lee Alekel. "We're too pill-happy in this country."
Then there's safety. Isoflavones are the plant kingdom's equivalent of estrogen. And that could make them dangerous for people who don't need any more of the hormone.
"We really don't know if taking large amounts of extracted isoflavones is safe for women," says Mindy Kurzer of the University of Minnesota. "For instance, I wouldn't advise a woman with a higher risk of breast cancer to take them." (Estrogen raises the risk of breast cancer.) And there is some evidence that isoflavones may stimulate the growth of advanced prostate tumors in animals.
Finally, the quality of isoflavone supplements is questionable.
"Labs have measured the isoflavone levels in commercial supplements and found tremendous variation in the amounts they contain," says Coral Lamartiniere of the University of Alabama at Birmingham.
In 2000, Kenneth Setchell of the University of Cincinnati College of Medicine and his colleagues analyzed 31 commercial isoflavone supplements or extracts. (1) Sixteen contained significantly less isoflavones than their labels indicated.
Even more alarming: Many of the supplements contained compounds that the researchers couldn't even identify.
"We know that high levels of isoflavones can cause reproductive problems in animals," Setchell points out. "There is little reason to believe that adverse effects could not occur in humans as a result of excessive intakes of some of these compounds."
(1) Journal of Nutrition 131: 1362S, 2001.