FRIDAY, Jan. 27, 2006 (HealthDay News) -- Americans who depend on soy to protect them from heart disease, cancer and other ills may want to think again.
Soy protein, for years touted as the health-conscious way to reduce cholesterol, isn't so effective, according to a new review of studies.
In a report from the American Heart Association (AHA), experts say the favorable effect of soy on so-called LDL "bad" cholesterol and other heart disease risk factors has not been confirmed by studies reported during the past decade.
The findings could change U.S. Food and Drug Administration rules regarding claims made by soy product manufacturers.
Earlier studies had suggested that consumption of at least 25 grams of soy protein a day could reduce cholesterol, and in 1999 the FDA allowed manufacturers to claim that soy products might cut the risk of heart disease risk. In 2000, the American Heart Association also recommended soy be included in a diet low in cholesterol and saturated fat.
In the wake of the latest report, the FDA is looking at the science, "including the AHA study," according to an agency spokeswoman. The FDA may decide that a re-evaluation of the soy claim is needed, she said.
The new review will appear in the Feb. 14 issue of Circulation.
No one's advising that people abandon soy-rich foods such as veggie burgers and tofu. Soy foods are "generally good foods, low in saturated fat and cholesterol," said Dr. Frank M. Sacks, a professor of nutrition at the Harvard School of Public Health, and lead author of the report.
However, "soy foods were given an extra boost from the idea that soy protein somehow has special properties to lower cholesterol," he said. "But that is not the case."
The AHA decided to re-examine the issue as more studies came out refuting soy's earlier promise. The committee, led by Sacks, reviewed 22 studies on soy protein. They found that large amounts of the nutrient in the diet reduced so-called LDL "bad" cholesterol by only about 3 percent, and had no effect on the so-called HDL "good" cholesterol. Soy-rich diets also had no significant effect on blood pressure.
The committee also looked at 19 studies that evaluated isoflavones, the bioactive molecules found in soy. They, too, had no effect on lowering blood levels of bad cholesterol or triglycerides, another heart disease risk factor, or on improving good cholesterol.
The committee also reviewed studies of soy protein and isoflavones on menopause-related symptoms, such as hot flashes. Again, they found the compounds had no effect in easing these symptoms.
"It's a little unusual for the Heart Association to go beyond the heart," Sacks said. But he said the panel decided to evaluate hot flash claims because they knew people would ask.
Finally, the evidence that soy isoflavones could help prevent breast, prostate and endometrial cancer was "inconclusive," Sacks said. While soy prevented the development and growth of prostate cancer in animal models, human studies showed it did not reduce prostate-specific antigen (PSA), a marker of prostate cancer development.
And Sacks noted that soy may also spur the unhealthy growth of cells in the breast.
The bottom line: "We feel really there is no reason why anyone should take isoflavone supplements," he said.
Not everyone agreed with the new findings. For instance, the National Prostate Cancer Coalition issued a press release, claiming the new soy study was misunderstood. "Soy does help in the fight against prostate cancer," it read in part.
"We believe the soy slows the progression of prostate cancer," said Jamie Bearse, a spokesman for the Washington, D.C.-based coalition. Bearse and the coalition experts point to studies that suggest soy works to slow the growth of prostate cancer. They pointed also to Asian diets, where soy is a staple food. Prostate cancer rates in Asia are much lower than in the United States, they said.
But Sacks said the lower rates in Asia may be due to more than diet.
And he isn't suggesting anyone give up on consuming soy, but just be realistic as to how much good it will do you. Sacks said the protein in soy is just as good -- but probably not better -- than the protein found in fish.
"Soy products are generally good for your cardiovascular health if they replace other adverse foods like [meat] burgers," Sacks said. "Have a soy burger instead of a hamburger, tofu in pasta instead of meatballs."
More information
To learn more about heart health, visit the American Heart Association.
