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Peak Wellness, Inc 50 Holly Hill Lane Greenwich, CT 06830 E-mail: peakwell{at}idt.net
Department of Internal Medicine Greenwich Hospital 6 Perryridge Road Greenwich, CT 06830-4697
Dear Sir:
Teixera et al (1) concluded that "consuming as little as 20 g soy protein/d instead of animal protein for 6 wk reduces concentrations of non-HDL cholesterol and apo B by 2.6% and 2.2%, respectively." This appears to be an incorrect conclusion considering the data and discussion put forth by these authors. In keeping with the given protocol of evaluating the effects of various levels of soy protein supplementation (soy with or without casein) in moderately hypercholesterolemic adults, their conclusion does not match the test. Specifically, the group who received 20 g isolated soy protein (ISP) also received 30 g casein; additionally, only the groups who received either 50 g ISP or casein did not receive a mix of the 2 proteins. Given that only the macronutrient and isoflavone contents of the diet were quantified and that actual meat, soy, or other lipid-affecting nutrients were not evaluated, the authors' conclusions become weak. Furthermore, the conclusion that ingesting 20 g ISP/d instead of animal protein for 6 wk reduces non-HDL cholesterol is both misleading and inaccurate.
In the apparent zeal of the authors to show the positive effect of small, daily servings of soy on lipid profiles, they mistakenly labeled non-HDL cholesterol. The authors state that non-HDL cholesterol equates to subtracting HDL from total cholesterol (TC), the error is within the framework of labeling non-HDL as VLDL + LDL cholesterol. Simply stated, the authors had the means to measure actual VLDL and LDL because they had measured TC, HDL, triacylglycerol, lipoprotein(a), apolipoprotein A-I, and apolipoprotein B. Thus, with all of the technical machinery available to the authors for firsthand measurement of these various lipids, it is questionable for them to put forth that observed changes in mathematically determined VLDL and LDL are accurate and truly reflective of the non-HDL lipid pool. Although it can be said that 65–70% of TC is carried as LDL, 10–15% as VLDL, and 20% as HDL and that there are various subfractions of LDL, we cannot accept the conclusion of the authors as a true measurement of non-HDL cholesterol (2).
Certainly, the role of soy and soy protein as medicinal foods for the treatment of mild to moderate hypercholesterolemia deserves more independent prospective trials to further determine both the risks and benefits of including this food in the Western diet. However, before we accept generalized conclusions such as those made in Teixera et al's article, we must insist on a strong body of evidence. Such a body of evidence must be in place before we can make recommendations to patients or to the general public. There is still more to learn about soy.
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