Is Soy Safe -- or Scary?
A study I reported on briefly in yesterday's health section suggests a possible link between men's soy intake and reduced sperm concentration. The Soyfoods Association of North America quickly issued a statement debunking that study.
This isn't the first time soy's risk/benefit ratio has been called into question. In fact, the health effects of soy-based foods and dietary supplements are poorly understood and hotly debated.
Interest in soy as a health-promoting food stems from the observation that populations that have historically consumed a lot of soy -- particularly Asians who eat lots of tofu, miso, and tempeh -- have typically enjoyed good health and have lower incidence of such diseases as breast cancer. But nobody knows for sure whether those good outcomes are directly related to eating soy or to some other aspect of these people's lives and behaviors.
Soy and the isoflavones it contains have been touted for their cancer-fighting capacity and cardiovascular benefits. Isoflavones are thought to behave in the body in much the way that estrogen does, but scientists haven't quite figured out whether they work for good or for ill -- or both.
According to Connie Weaver, head of the department of foods and nutrition at Purdue University, flaws have recently been recognized in the research methodology on which our current understanding of soy's pros and cons are based. Much of that research has been in animals, she says, and apparently nobody thought to take into account the compounds -- potentially including those that have estrogenic effects -- that may have been in the chow those animals were fed. "A lot of what we thought we knew is confounded," Weaver says. "And we can't go back and unravel it because nobody was keeping track" of what the animal subjects were fed.
On top of that, she says, soy research is inherently complicated: There are so many varieties of soy, soy-based products and soy derivatives, any of which might have different effects depending on who consumes them and at what stage of their life they do the consuming. It's possible, for instance, that a person who has eaten soy all her life may enjoy protection against breast cancer, while a woman who already has an estrogen-sensitive tumor when she starts eating soy will find her cancer is exacerbated, Weaver explains.
None of this is news to the National Institutes of Health (NIH); that agency plans a workshop next April to address human soy studies and to grapple with issues raised in this 2005 report. In the meantime, the Web site for NIH's Center for Complementary and Alternative Medicine (NCCAM) says the agency has included basic and clinical research into soy protein and soy isolates among the areas of research from which it's taking a brief "pause."
For what it's worth, here's the federal government's most up-to-date assessment on soy. In short, based on the best available evidence, science strongly suggests that soy is a good source of protein and that it may lower overall cholesterol and low-density lipoproteins (LDL, or "bad" cholesterol) moderately. But it's not been shown that that translates into fewer heart attacks or strokes.
Science is more wishy-washy, but generally supportive, when addressing the idea that soy may help ward off diarrhea in infants and young children and ease some symptoms of menopause (such as hot flashes).
For all the other health benefits -- including those related to cancer and cardiovascular health -- attributed to soy intake, the government-funded analysis (issued in March by the independent Natural Standard Research Collaboration) finds inconclusive or contradictory evidence.
So what's your stance on soy? Do you eat soy-based foods because you like them? Or because they're supposed to be good for you? Do you feel your health's better because you eat soy? Or do you worry about soy's possible risks?
Jennifer LaRue Huget
July 30, 2008; 7:00 AM ET
Categories: Alternative and Complementary Medicine
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