Is it a joy to eat soy?
July 8, 2003 | 12:00am
Soy has gone from ordinary taho to cult food. It is everywhere. Even Americans now spend $3.3 billion each year for tofu, tempeh, soy nuts, soy milk, and "power" bars. "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 reality: It can ... but you’ve got to eat a lot.
In the early 1990s, there were already 38 well-conducted clinical trials which showed that soy lowers blood cholesterol levels. By 1999, the US Food and Drug Administration (FDA) told manufacturers that their labels could claim that soy can help reduce the risk of heart disease, but with few stipulations. The FDA 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 to 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 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 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 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.
Soy is the most popular supplement for coping with the symptoms of menopause. And alternatives to estrogen-progestin for menopause are "a hot market," says Rieva Lesonsky of Entrepreneur magazine. "There’s no question that this is going to be a lucrative market for at least the next 15 to 20 years," he adds.
But to make money selling soy for menopause, companies will have to ignore most of the research. Six published studies or soon-to-be-published studies in the US – from MIT, Tufts 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 Dr. Lee Alekel of Iowa State University. "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 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."
Two studies on Chinese and Asian-American women showed that those who have consumed at least one serving of soy foods a week during adolescence had a significantly lower risk of breast cancer than those who ate little or no soy.
"What soy seems to do during early life," says Carol Lamartiniere of the University of Alabama, "is stimulate 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." 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 when signs of breast cell proliferation were found in some premenopausal women who ate soy regularly for a few weeks to a few months. Cell proliferation may raise the risk of breast cancer. Postmenopausal women were unaffected. But the alarm may have been premature. A further analysis of added data from more subjects showed that the impact of soy on breast cells was no longer statistically significant.
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 Kurzer.
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. 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. Their risk of spinal osteoporosis is 40 to 50 percent higher than Americans. So why do the Japanese suffer fewer hip fractures than 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. "These studies, however, have been for short periods of time or involved small numbers of volunteers," says William Wong of the Baylor College of Medicine.
Two large, long-term studies are being planned – at Baylor and at Iowa State University. "These studies will try to answer the three questions everyone wants answered," says Wong. "Do soy isoflavones work? Are they safe? And, if they do work, how much should you take?"
The bottom line: Until the results of more studies are in, the impact of soy or its isoflavones on bones is far from clear.
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