Taking a closer look at soy
Health food advocates have long claimed that soy, the little legume used in tofu burgers and smoothies, can protect against heart disease, ward off cancer and combat hot flashes. Those claims are coming under scrutiny now that a soy food manufacturer is seeking government approval to tout on its labels soy’s supposed cancer-fighting abilities.
The company’s petition to the Food and Drug Administration for a new health claim has the support of some soy researchers but has angered others who say the science simply isn’t there to support it.
Some controversial research in mice even suggests that soy could promote breast cancer. The FDA, which has loosened its rules on what products do and don’t deserve to be sold with health claims, is accepting public comment on the issue this month.
The company, Solae of St. Louis, wants its labels to say, in part, that “scientific evidence suggests that consumption of soy protein may reduce the risk of certain cancers”; in other materials, the labels would name cancers of the breast, colon and prostate. The company cites 58 studies in support of its position but also asks that the labels carry the caveat: “However, this evidence is not conclusive.”
Indeed, the evidence is not conclusive. Most comes from epidemiological studies, which look at groups of people to find associations between their habits, such as soy consumption, and their risks of getting diseases. Such studies, however, are not designed to prove that certain behaviors cause or protect against diseases.
Dr. David Heber, director of the Center for Human Nutrition at UCLA, is sympathetic to Solae’s claim. “Soy is an important tool in helping women achieve their personal best body weight and shape, and obesity is a major contributor to breast cancer risk,” he said.
But leaping from that to the idea that eating soy can help prevent cancer and other diseases is dangerous business, said David Schardt, a senior nutritionist at the Center for Science in the Public Interest, a nutrition advocacy group in Washington, D.C. “It doesn’t make sense to urge people to consume these products when we don’t know whether they prevent cancer or make matters worse,” he said.
The notion that soy could make matters worse makes some theoretical sense. Soybeans are rich in weak plant estrogens, specifically genistein and daidzein, which are called isoflavones. Like the estrogens that humans make in their bodies and buy by prescription, these estrogens could theoretically spur the growth of estrogen-dependent breast cancer cells. Some hints come from the laboratory of Bill Helferich, a professor of Food Science and Human Nutrition at the University of Illinois. He has found that genistein from soy can promote the growth of human breast tumors implanted into mice.
In Asia, he said, soy is consumed in minimally processed forms such as tofu, and Asians do have a lower incidence of breast cancer than Americans. The whole soybean contains 30% to 40% protein. But many soy products in the U.S. are highly concentrated and contain up to 90% protein. The concentrated products still contain isoflavones but may be missing potentially beneficial but unidentified compounds, he said. Heber of UCLA argues that Helferich’s mouse model is flawed because mice are missing an enzyme in human fat cells that controls estrogen metabolism.
Soy has been losing its luster for several years. Nearly five years ago, the FDA became so convinced of soy’s capacity to lower cholesterol that it began allowing manufacturers to put health claims on soy products indicating that it may lower heart disease risk.
But since then, the emerging data “has not upheld that health claim,” said Alice Lichtenstein, a professor at the Friedman School of Nutrition Science and Policy at Tufts University in Boston. It turns out, she said, that soy has “very little effect” on lowering “bad,” or LDL, cholesterol. Others note that soy can reduce heart disease risk when it is substituted for greasy meat.
Nor has soy lived up to its promise for combating hot flashes, said Dr. Sherwood Gorbach, professor of community health and medicine at Tufts University School of Medicine, who only a few years ago was developing a soy supplement for hot flashes and has now abandoned that effort. “We have a patent,” said Gorbach, “but the evidence was not compelling.”
But the real battle now is over soy’s alleged anti-cancer properties, and how that goes depends on new thinking at the FDA -- which recently weakened its rules on health claims for food and dietary supplements.
In 1990, Congress passed a statute, the Nutrition Labeling and Education Act, which required that FDA-approved health claims for food be based on “significant scientific agreement,” said Bruce Silverglade, director of legal affairs for the Center for Science in the Public Interest, a nutrition advocacy group based in Washington, D.C.
The food industry objected, arguing that this requirement violated its First Amendment rights to free speech. The FDA ignored the industry’s argument until 2002, when it said it would “permit health claims for foods even if there is no significant scientific agreement” on the benefits, Silverglade said.
Last July, the FDA announced it would allow some food companies to make “qualified” health claims, the weaker claim Solae is seeking. In September, Silverglade’s group and a Washington-based advocacy group, Public Citizen, sued the FDA over this change in policy. A ruling is pending.
