Effects of Two Types of Soy Milk and Dairy Milk On Plasma Lipids in Hypercholesterolemic Adults
In the past 30 years, several clinical trials have investigated the cholesterol-lowering potential of soy protein. Earlier studies concluded that soy protein is an effective strategy to lower cholesterol, leading the FDA to approve a health claim for soy protein at a dose of 25 grams/day. However, more recent trials have found the cholesterol-lowering power of soy protein to be much more modest that that reported by the earlier trials, and not clinically significant. Several differences in the designs of the studies may explain these conflicting results. In addition, most trials used soy protein isolate (a product manufactured by grinding soy beans into a powder and depriving them of all their fat) and very few have evaluated the effect of more traditional, less processed Asian foods such as soy milk or tofu, which contain other beneficial nutrients in addition to the soy protein.
A rigorous trial was conducted to examine the effect of soy milk intake on blood lipid levels in 28 adults with high LDL-cholesterol levels. Two different types of soy milk were compared, one made from whole soy beans and one made from soy protein isolate, with dairy milk (control) to determine whether differences in proteins and other characteristics would affect the results.
In this trial, participants drank soy or dairy milk 3 times a day in a “cross-over design.” They alternated drinking each type of milk for four weeks, with a “washout” period of four weeks between each phase of the study.
At the completion of all three phases, LDL-cholesterol was modestly reduced at the end of the soy milk phases compared to the dairy milk phase, with no differences between the two kinds of soy milk.
Interestingly, three quarters of participants found that drinking about 3 cups of soy milk a day was “too much” to continue on on a long-term basis.
To learn more about the details of the study, read:
- Abstract, published in Journal of the American College of Nutrition