Soy and Cholesterol

In 1999, FDA approved a health claim for soy and heart disease, after reviewing 27 clinical trials that substituted soy protein for animal protein and found reductions of blood cholesterol in individuals with normal and elevated levels. Since then, science has continued to support the health claim for soy. Three articles published in 2007 provide new evidence for soy’s role in managing cholesterol.

Fresh eyes on the original research

A review by well-known cardiologist Cesare Sirtori, M.D.,Ph.D., University of Milano, Italy, published in the May issue of British Journal of Nutrition, re-examined the studies Dr. James Anderson from University of Kentucky used in a 1995 meta-analysis that found a 9.3% drop in total cholesterol and a 12.3% drop in LDL (bad) cholesterol, when soy was substituted for animal protein. Sirtori and his colleagues grouped the initial studies, as well as 33 studies conducted after 1995, according to baseline levels of cholesterol and separately calculated the cholesterol-lowering effect of soy for each group. Sirtori found that Anderson’s original results, when examined by cholesterol level, almost perfectly predicted results of the later studies.

Sirtori and his colleagues believe soy protein may have a ‘pharmacological effect’ on blood lipids. In all of the later studies examined, soy was only partially substituted for animal protein or added to a regular diet. This demonstrates that soy protein’s cholesterol-lowering effect is not merely observed when it replaces foods high in cholesterol and saturated fat.

Cholesterol-lowering effect of soy protein is independent from soy isoflavones

A review, published in the April issue of American Journal of Clinical Nutrition, looked across 11 controlled diet studies using soy protein. In all the studies, subjects consumed soy protein either with or without soy isoflavones, compounds that occur naturally in soybeans. Researchers concluded that cholesterol levels improved both in those people who ate soy protein alone, as well as in those who had soy protein with isoflavones. This review adds to building evidence that soy’s lipid-lowering action may be enhanced when isoflavones are provided with soy protein, and reinforces an independent effect of soy protein on blood cholesterol.

Soy protein in clinical trials

The Jan.-Feb. issue of Menopause reported on a randomized, double-blind, controlled clinical trial using 216 postmenopausal women. All participants consumed a casein protein-based powdered supplement, to be mixed with beverages, for 4 weeks. Then participants were randomized to continue the current supplement or switch to a soy protein-based one. After 12 more weeks, those using the soy supplement experienced significant reductions in LDL cholesterol, compared to those on the casein supplement. Similar results were found in another clinical trial published in the March issue of American Journal of Clinical Nutrition. In this study, 42 postmenopausal women with metabolic syndrome lowered their cholesterol after 8 weeks of replacing a daily serving of red meat with soy protein.

Scientific evidence continues to support soy protein’s ability to modestly lower LDL cholesterol and triglycerides by about 3-6%, which is consistent with the American Heart Association’s finding of a 2-7% decrease in LDL cholesterol. From a public health perspective, a 3% reduction in LDL cholesterol reduces mortality by 6%. Recommending soyfoods to your patients ensures they Feel Alive with 25!

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References:

  1. Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. N Engl J Med. 1995 Aug 3;333(5):276-82.
  2. Sirtori CR, Eberini I, Arnoldi A. Hypocholesterolaemic effects of soya proteins: results of recent studies are predictable from the Anderson meta-analysis data. Br J Nutr. 2007 May;97(5):816-22.
  3. Taku K, Umegaki K, Sato Y, Taki Y, Endoh K, Watanabe S. Soy isoflavones lower serum total and LDL cholesterol in humans: a meta-analysis of 11 randomized controlled trials. Am J Clin Nutr. 2007 Apr;85(4):1148-56.
  4. Allen JK, Becker DM, Kwiterovich PO, Lindenstruth KA, Curtis C. Effect of soy protein-containing isoflavones on lipoproteins in postmenopausal women. Menopause. 2007 Jan-Feb;14(1):106-14.
  5. Azadbakht L, Kimiagar M, Mehrabi Y, Esmaillzadeh A, Padyab M, Hu FB, Willett WC. Soy inclusion in the diet improves features of the metabolic syndrome: a randomized crossover study in postmenopausal women. Am J Clin Nutr. 2007 Mar;85(3):735-41
  6. Sacks F, Lichtenstein A, VanHorn L, et al. Soy protein, isoflavones, and cardiovascular health. Circulation. 2006:113:1-12.