(18-09-06) Soy not as good for the heart as thought: report

By Amy Norton

NEW YORK (Reuters Health) - Tofu and other soy products may not do much for a person's cholesterol levels after all, an American Heart Association panel has concluded.

In a review of 22 clinical trials, researchers with the AHA's nutrition committee found that large amounts of isolated soy protein helped lower study participants' "bad" cholesterol by only about 3 percent on average.

The change is less than impressive considering the large doses of soy protein used in the studies, according to the AHA panel.

Supplements containing isoflavones -- estrogen-like compounds found in soybeans -- appeared even less effective. In 19 studies, the effect of isoflavones on LDL, or "bad," cholesterol was generally "nil," Dr. Frank M. Sacks and other committee members report in the AHA journal Circulation.

Beyond LDL cholesterol, soy protein and isoflavones have shown no influence on levels of other blood fats or blood pressure, the panel says. Evidence is also lacking when it comes to preventing or treating a range of other conditions -- menopause symptoms, osteoporosis and breast, prostate and uterine cancers.

A number of early studies had found that diets rich in soy protein -- found in tofu, soy milk and other foods -- might help lower LDL cholesterol, and possibly raise levels of the heart-healthy HDL cholesterol. Based on this evidence, the Food and Drug Administration (FDA) in 1999 gave the go-ahead for soy-containing foods to claim a heart benefit on their labels.

In 2000, the AHA nutrition committee issued a statement recommending that people include soy protein in their diets. This latest report is an update of that statement, given that a number of well-designed studies on soy protein have been conducted since the last recommendations were issued, according to the AHA.

Based on these more recent trials, the committee members note, there is no basis for recommending isoflavone supplements. And for its part, soy protein seems to have no special cholesterol advantage over other vegetable proteins, Sacks told Reuters Health. "Soy protein does lower cholesterol, but by a very small amount," he added.

"But," he stressed, "diet has a big effect on cholesterol." And since soy-based foods are considered healthy choices, Sacks said, they should be included in a heart-friendly diet.

According to the AHA panel, replacing animal protein with soy protein -- having a soy burger instead of a hamburger, for instance -- would presumably help heart health because soy products have little to no saturated fat and cholesterol, but do have healthful fatty acids, fiber, and vitamins and minerals.

The panel's review also included research on whether soy protein or isoflavone supplements help fight hot flashes, osteoporosis and certain cancers. Because isoflavones have both estrogen-like and anti-estrogen actions, scientists have been interested in whether the substances can lower the risk of or help treat diseases influenced by the hormone.

Overall, Sacks said, the evidence on hot flashes is "not impressive," while research findings have been mixed regarding osteoporosis.

The evidence is also "meager" as to what effect, if any, soy isoflavones have on tumors of the breast, prostate and uterine lining, according to the AHA committee.

There is even a "little worry" over possible adverse effects, Sacks said, given that a few women in one trial showed abnormal cell growth in the uterine lining -- a potential precursor to cancer.

SOURCE: Circulation: Journal of the American Heart Association, January 23, 2006.

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