(March 2001)

Soybean products contain estrogen-like substances called isoflavones. Reporting in the Archives of Internal Medicine, investigators from Wake Forest University School of Medicine studied 156 healthy men and women who were given soy protein for nine weeks. Subjects were chosen if they had moderately elevated blood levels of cholesterol and its dangerous component low-density lipoprotein cholesterol (LDL - so called bad cholesterol). They averaged 52 years of age. The 156 men and women were divided into five groups; one acted as controls, the other four got increasing amounts of pure soy protein. Those who received the highest dosage of soy protein showed a modest 4 percent fall in total cholesterol and LDL cholesterol with about a 10 milligram drop from 243 to 233 in total cholesterol and 166 to 156 in LDL. A more impressive 9 percent reduction was found among those who started off with higher blood cholesterol and LDL levels and were given the highest soy protein dosage; they experienced a drop in total cholesterol from 260 to 237 and of LDL from 181 to 163 milligrams. In those with the higher cholesterol levels at the start of the study, those given the second to largest amount of soy protein also showed significant total cholesterol and LDL reductions.

Commentary: Soy products can now join oatmeal and other soluble fibers and certain margarine-like products that can lower total cholesterol levels and LDL levels in the blood to a modest extent. Although there are no persuasive and convergent data showing that oat fiber or soy products or the new cholesterol lowering margarine-like spreads actually do lower the risk of heart attacks, it does seem reasonable that the modest cholesterol lowering will translate into some benefit in lowered heart attack risk. A 10 milligram drop in cholesterol or LDL levels should result in a 20 percent drop in heart attack rates. Unfortunately, the amount of cholesterol lowering is very variable; some people get no lowering, some moderate reduction, some more impressive lowering. A low fat diet and weight loss are likely to be more effective than eating soy products, oat fiber, or using the cholesterol lowering margarine-like spreads; nevertheless, including one or all three in your diet can be helpful in cholesterol control.

The authors of this study did not tell us how much of soy products we have to eat to achieve moderately lower cholesterol and LDL levels. Other studies suggest 40 to 50 grams a day will be adequate.

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But don’t expect dramatic results - the most you can realistically expect is a 4 or 5 percent reduction. To get a bigger reduction requires the addition of a general low fat diet and, if possible, weight loss. Additionally, those with elevated cholesterol and LDL levels must be under a doctor’s care to be sure there are regular blood cholesterol determinations to see whether and when one of the very effective cholesterol-lowering drugs should be added.

Will including both soy products and oat fiber in your diet and, at the same time, using cholesterol-lowering margarine-like spreads result in much greater cholesterol lowering than using only soy products (or only oat fiber)? That is not yet known.

Crouse, J.R. III, et al. A randomized trial comparing the effect of casein with that of soy protein containing various amounts of isoflavones on plasma concentrations of lipids and lipoproteins. Archives Internal Medicine. Vol 159. (September 27) Pgs 2070-2076. 1999.