By Jeremy Appleton, ND, CNS
Healthnotes Newswire (December 7, 2006)—When it comes to controlling cholesterol, the goal is to lower the “bad” cholesterol (LDL) and raise the “good” cholesterol (HDL). Some studies have shown that soy protein can do just that, plus lower high triglycerides, which are a risk factor for heart disease. Because there have been conflicting results on soy protein’s effects on cholesterol, doctors have been unable to agree on whether or not to recommend it. The new study aimed to answer this question.
“We examined the effect of soy protein supplementation on lipid levels by pooling the results from 27 randomized controlled trials,” said Kristi Reynolds, PhD, MPH, assistant professor of epidemiology at Tulane University School of Public Health and Tropical Medicine. Dr. Reynolds, the lead author of the new review, continued, “With a total of 41 comparisons in our analysis, we were able to come up with a precise and unbiased estimate of the effect of soy protein on cholesterol and triglyceride levels.”
This type of study, known as a meta-analysis, is a useful way for researchers to make sense of diverse results from many studies. Only randomized controlled trials were included in the meta-analysis. (In such trials, participants are randomly assigned to receive either an active treatment or a placebo, and neither the participants nor the researchers know which they are receiving until after the results are interpreted. This type of “blinded” study makes it more difficult for results to be deliberately or unwittingly influenced by the people involved.) Researchers also considered issues such as quality of the study design, publication bias (for example, a tendency to suppress research with negative outcomes), and the special characteristics of subgroups (for example, smokers, ethnic groups, age, and gender).
After reviewing all the qualified studies, researchers concluded that supplementing with soy protein lowers total cholesterol, LDL cholesterol, and triglycerides and slightly increases HDL cholesterol. These effects were found to be smaller than those reported in previous meta-analyses, probably because of differences in the criteria for what studies could be considered. For example, only English language studies were considered, which could exclude much high-quality research.
“Our results indicate that soy protein supplementation reduces serum lipids among adults with or without high cholesterol levels,” said Dr. Reynolds. “Based on these findings, we recommend that people replace foods high in saturated fat, trans-saturated fat, and cholesterol with soy protein. The evidence indicates that this may reduce the risk of heart disease.”
Sources of soy protein include soy milk, tofu, and tempeh.
(Am J Cardiol 2006;98:633–40)
Jeremy Appleton, ND, CNS, is a licensed naturopathic physician, certified nutrition specialist, and published author. Dr. Appleton was the Nutrition Department Chair at the National College of Naturopathic Medicine, has served on the faculty at Bastyr University of Natural Health Sciences, and is a former Healthnotes Senior Science Editor and a founding contributor to Healthnotes Newswire. He has worked extensively in scientific and regulatory affairs in the supplement industry and is now a consultant through his company Praxis Natural Products Consulting and Wellness Services.
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