Meta-analysis finds soy protein improves lipids

The results of an analysis of 41 randomized controlled trials, published in the September 1, 2006 issue of the American Journal of Cardiology found that supplementing the diet with soy protein significantly lowered triglycerides and total and low-density lipoprotein (LDL) cholesterol, while raising high-density lipoprotein (HDL) cholesterol.

Researchers at Tulane University in New Orleans, led by assistant professor of epidemiology at the Tulane School of Public Health and Tropical Medicine Kristi Reynolds, PhD, selected 27 reports providing 41 comparisons in which isolated soy protein supplementation was the only intervention and changes in serum lipids were reported. The studies were conducted from 1982 and 2004 and included a total of 1,756 participants. The amount of isolated soy protein administered in the trials ranged from 20 to 61 grams per day.

The results of the analysis found an average 5.26 milligram per deciliter reduction in total cholesterol, a 4.25 mg/dL reduction in LDL, a 6.26 mg/dL reduction in triglycerides, and a 0.77 mg/dL increase in HDL cholesterol. The effect was greater with a higher intake of soy, and among women who were not postmenopausal. Soy showed a greater beneficial impact on HDL in trials of longer duration and among individuals with higher cholesterol.

The authors remark that previous meta-analyses of soy’s effect on lipids found stronger effects for soy, which may be due to the inclusion of nonrandomized studies, or the use of a variety of soy protein products. “Our results support the notion that soy protein should be an important component of a comprehensive dietary intervention for the prevention and treatment of hypercholesterolemia,” they conclude, however, they recommend that reduced dietary intake of cholesterol and saturated and trans fats, combined with an increase in polyunsaturated fats should remain the focus of cholesterol-reducing dietary interventions.

Health Concern

Cholesterol reduction

Soy has been a staple part of the Southeastern diet for nearly 5,000 years and is associated with a reduction in the rates of cardiovascular disease, and certain types of cancer. The research is now showing that phytochemicals in soy are the mechanism of action responsible [Society for Experimental Biology and Medicine (United States), 1998, 217[3]:386-92].

Diets rich in soy protein can protect against the development of atherosclerosis. The mechanisms of action of soy protein include cholesterol lowering, inhibition of LDL oxidation, protection against the development of atherosclerosis, and reduction in risk of thrombosis. The active constituents in soy responsible for these benefits are the isoflavones genistein, daidzein, and glycitein. In a study to determine whether soy isoflavones would protect against atherosclerosis in mice, it was reported that mice fed a soy diet averaged 30% lower cholesterol (J Nutr [United States], June 1998, 128[6]:954-59).

In a study in Metabolism, June 1997, investigations suggest that dietary soybean protein has a beneficial effect on cardiovascular risk factors. According to another study completed at about the same time, "Potential mechanisms by which soy isoflavones might prevent atherosclerosis include a beneficial effect on plasma lipid concentrations, antioxidant effects, antiproliferative and antimigratory effects on smooth muscle cells, effects on thrombus formation, and maintenance of normal vascular reactivity" (American Journal of Clinical Nutrition, Dec. 1988, 68[6] Suppl., 1390S-93S).

Adding to the evidence that soy is beneficial, conclusions of a September 1998 Journal of Nutrition study are that "the efficacy of the American Hospital Association Step I cholesterol-lowering diet can be improved with the addition of soy protein." If you want to reduce your disease risk to heart disease and avoid elevated cholesterol levels, it is recommended that you use soy.