Soy Isoflavones
Soy Protein with Isoflavones, but not an Isoflavone Supplement, improves Blood Cholesterol Levels and reduces the risk of Atherosclerosis
What is the problem and what is known about it so far?
Atherosclerosis, or the process in which fatty deposits build up in the lining of arteries, is a major cause of cardiovascular disease (CVD) and death in the United States. One of the major risk factors for developing atherosclerosis is high blood cholesterol (hypercholesterolemia). Fortunately, cholesterol levels can be improved in many people simply by adopting a low-fat diet and eating certain beneficial foods. Many studies have shown that eating soy protein, such as is found in tofu and soy milk, can improve cholesterol levels and reduce the risk of developing atherosclerosis. This effect is believed to be caused by a class of compounds in soy called isoflavones. Exactly how isoflavones reduce cholesterol, and what forms of soy are most beneficial, are areas of ongoing research.
Why did the researchers do this particular study?
The researchers wanted to identify ways that soy protein could help to decrease atherosclerosis, in arteries.They also wanted to determine if taking isoflavones in pill or powder forms could have similar effects to eating soy.
Who was studied?
60 adult female monkeys imported from the Indonesian Primate Center were studied
How was the study done?
The monkeys were all fed the same diet for the 2 months prior to the study. Then the researchers randomly divided the monkeys into three groups of 20, and the groups were fed different diets over the next 20 weeks. The first group was fed a standard protein source derived from milk, the second group was fed the same standard protein source along with isoflavones separated from soy, and the third group was fed whole soy protein. Blood cholesterol levels were checked at various points during the study, and sections of several major arteries were examined at the end of the study to determine how much cholesterol had been taken up by the lining of those arteries.
What did the researchers find?
The researchers found that the monkeys that were fed soy protein had significant improvements in cholesterol levels, with no such improvement seen in the groups that were fed a standard protein source or a standard protein source with isoflavones separated from soy. Similarly, examination of arteries in the monkeys that were fed soy protein showed 50% less cholesterol than the other two groups.
What were the limitations of the study?
While monkeys are more similar to humans than other animals used in studies, it is difficult to say if the results are applicable to humans. However, the results are consistent with other studies that have been done with humans.
What are the implications of the study?
This study provides further support of the beneficial effects of soy on cardiovascular health, while suggesting that isolated isoflavone supplements, commonly sold in pill or powder form, may not be as effective.
Summarized by Kurt H. Kelley, College of Medicine, University of Vermont
Summarized from "Soy Protein With Isoflavones, but not an Isoflavone-Rich Supplement, Improves Arterial Low-Density Lipoprotein Metabolism and Atherogenesis." Wagner, JD et al. Arteriosclerosis, Thrombosis, and Vascular Biology. December 2003, Volume 23, Number 12, pages 2241 - 2246.
