Effects of Dietary Soy Protein on Atherosclerosis

Effects of Dietary Soy Protein on Iliac and Carotid Artery Atherosclerosis and Gene Expression in Male Monkeys.

Dietary soy has long been thought to have positive health benefits with respect to atherosclerosis-related disease (14). However, the roles of the individual soy components, as well as the mechanisms underlying the beneficial effects of soy are poorly understood. Soy protein isolate (SPI) is commonly used in experimental studies addressing possible cardiovascular benefits of dietary soy and is a basic component of many health foods and dietary supplements available to the general public. The major components of soy protein isolate (SPI) most often associated with the suggested cardiovascular benefits of soy are the protein/peptide fractions and the isoflavones (IF). IF are estrogen-like compounds found in soy beans, as well as many legumes and grains (5). The most abundant IF in soy products are daidzein, genistein, and glycitein. In addition, IF metabolites, such as equol, may contribute to the biological activity of dietary IF (5). IF are structurally similar to estradiol and known to interact with estrogen receptors, imparting estrogen agonist/antagonist activities in vitro and in vivo (6).

Studies with nonhuman primate models have demonstrated inhibitory effects of dietary SPI on atherosclerosis in both male (juvenile and adult) and female (adult) subjects (2, 3, 7). Sex as well as the timing of intervention may be important issues, as age and or amount of atherosclerosis at initiation may impact outcomes. In both sexes, SPI treatment has been associated with favorable changes in plasma lipid profiles, increasing plasma high density lipoprotein (HDL) cholesterol (HDLc) and decreasing non-HDLc (VLDLc + LDLc) levels. These changes in plasma lipids account for approximately 50% of the decrease seen in atherosclerotic plaque area in these studies (2, 7). Our data in post-menopausal female monkeys suggest that dietary soy IF may have anti-inflammatory properties (8), perhaps at the level of the artery wall, although the exact site of such an activity is unclear.
Recently we found that coronary artery atherosclerosis (CAA) in adult male monkeys was reduced by SPI (2). The objective of the present study was to compare and contrast the effects of dietary SPI on atherosclerosis and inflammation in the coronary, iliac and carotid arteries of male cynomolgus macaques. Inflammation was assessed in vascular sites and the liver by measurement of the expression of genes implicated as mediators of inflammation and atherogenesis. We also assessed expression of estrogen receptors as potential mediators of IF effects. We hypothesized that consumption of IF-containing SPI would have anti-inflammatory effects in arteries and/or the liver which would be accompanied by decreased atherosclerotic plaque area.

I’ll summarize this and find some more information and post it later. Basically, the monkeys who got the soy protein had significantly less plaque in there arteries than the other monkeys.

I got the following from the FDA

In October 1999, FDA approved a health claim that can be used on labels of soy-based foods to tout their heart-healthy benefits. The agency reviewed research from 27 studies that showed soy protein’s value in lowering levels of total cholesterol and low-density lipoprotein (LDL, or “bad” cholesterol).

Food marketers can now use the following claim, or a reasonable variation, on their products: “Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease. One serving of (name of food) provides __ grams of soy protein.” To qualify for the claim foods must contain per serving:

  • 6.25 grams of soy protein
  • low fat (less than 3 grams)
  • low saturated fat (less than 1 gram)
  • low cholesterol (less than 20 milligrams)
  • sodium value of less than 480 milligrams for individual foods, less than 720 milligrams if considered a main dish, and less than 960 milligrams if considered a meal.

Foods made with the whole soybean, such as tofu, may qualify for the claim if they have no fat other than that naturally present in the whole bean.