Soy Protein, Isoflavones, and Cardiovascular Health: A Summary of a Statement for Professionals From the American Heart Association Nutrition Committee

F. M. Sacks
2006 Arteriosclerosis, Thrombosis and Vascular Biology  
for the AHA Nutrition Committee T his editorial summarizes the recent American Heart Association (AHA) Science Advisory on soy protein and isoflavones (phytoestrogens) published in the February 21, 2006, issue of Circulation. 1 Soy protein and isoflavones have gained considerable attention for their potential role in improving risk factors for cardiovascular disease. This scientific advisory report assesses the more recent work published on soy protein and its component isoflavones. In 22
more » ... avones. In 22 randomized trials, isolated soy protein with isoflavones compared with milk or other proteins decreased LDL cholesterol concentrations in most studies; the average effect was approximately 3%. This reduction is very small compared with the large amount of soy protein tested in these studies, averaging 50 g, approximately half the usual total daily protein intake. No significant effects were evident on HDL cholesterol, triglycerides, lipoprotein(a), or blood pressure. Among 19 studies of soy isoflavones, the average effect on LDL cholesterol and other lipid risk factors was nil. Soy protein or isoflavones have not been shown to lessen vasomotor symptoms of menopause, and results are mixed regarding slowing of postmenopausal bone loss. The efficacy and safety of soy isoflavones for preventing or treating cancer of the breast, endometrium, and prostate are not established; evidence from clinical trials is meager and cautionary as regards a possible adverse effect. For this reason, use of isoflavone supplements in food or pills is not recommended. Thus, earlier research indicating that soy protein compared with other proteins has clinically important favorable effects has not enjoyed confirmation. In contrast, many soy products should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat. In October 1999, the US Food and Drug Administration (FDA) approved labeling for foods containing soy protein as protective against coronary heart disease. 2 The FDA based this decision on clinical studies showing that at least 25 g soy protein per day lowered total and LDL cholesterol. The FDA requires for the claim that a serving contain at least 6.25 g soy protein, 25% of the necessary daily amount, 25 g, expecting that foods containing soy protein would be eaten at least 4 times per day. The FDA also stated, "the evidence did not support a significant role for soy isoflavones in cholesterollowering effects of soy protein." In 2000, the AHA Nutrition Committee released a scientific advisory on soy protein and CVD. 3 Since then, many well-controlled studies on soy protein and soy-derived isoflavones substantially added to the knowledge base. This scientific advisory report assesses the more recent work published on soy protein and its component isoflavones, focusing on blood LDL cholesterol and other cardiovascular disease risk factors, HDL cholesterol, triglycerides, lipoprotein(a), and blood pressure. The medical literature was searched comprehensively for original research publications on the effects of soy protein or isoflavones on cardiovascular disease risk factors, and all controlled trials that separately listed soy protein and isoflavone content were used. Most studies exchanged soy protein for other dietary proteins, and this evidence is evaluated in this report. Much less is known about the potential impact on risk factors for CVD of increasing total protein intake by adding soy or other plant protein in place of carbohydrate or fat; this important dietary change is currently being studied. Animal proteins raise blood cholesterol concentrations in several animal species fed cholesterol-free semi-synthetic diets. 4,5 Casein, the most prevalent protein in milk, has been the most often used, although other animal proteins such as pork and beef protein do the same. In contrast, when soy protein is substituted for the animal protein, hypercholesterolemia does not occur. Diets similar to those eaten by humans, based on either soy protein or casein, were fed to rabbits, and casein produced hypercholesterolemia as expected. 6 However, when the same diets were fed to healthy people, the protein source did not affect blood cholesterol. 6, 7 In the late 1970s and early 1980s, Sirtori and colleagues found that diets high in soy protein, replacing nearly all the animal protein, substantially reduced blood cholesterol by 20% to 30% in severe hypercholesterolemia. 8 Because the soy protein diets were also reduced in saturated fat and cholesterol and increased in polyunsaturated fat, and because
doi:10.1161/01.atv.0000227471.00284.ef pmid:16857959 fatcat:2gcry3t7mrdkdnl7a4y34nfpoq