Reply to DS Kalman and CM Colker

Division of Nutritional Sciences University of Illinois at Urbana-Champaign Urbana, IL E-mail: j-erdman{at}uiuc.edu
Protein Technologies International/DuPont St Louis, MO
The Functional Foods for Health Program University of Illinois at Urbana-Champaign Urbana, IL

Dear Sir:

We reassert our conclusion that "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" (1). We fully agree with Kalman and Colker that there is much more to learn about soy. However, a strong body of evidence from several laboratories, including a meta-analysis, already exists on the effects of soy protein on blood lipids (2–4). The Food and Drug Administration (FDA) reviewed the extensive literature published on this subject and in October of 1999 approved a health claim for foods containing soy protein (5). The qualifying amount of soy protein approved in this health claim (25 g) is similar to and consistent with the amount of soy protein shown to decrease blood lipids in our paper (20 g). Therefore, the results of our study, in fact, provide additional support for the FDA-approved health claim.

The comment of Kalman and Colker regarding our conclusion may have resulted from a misunderstanding on their part of our study design. In our study, the control group received 50 g casein (ie, no replacement). For all other groups, different amounts of casein (20, 30, 40, and 50 g) were replaced by equivalent amounts of isolated soy protein, so that the total protein intake remained constant. Therefore, our conclusion about the replacement of animal protein with soy protein was indeed consistent with our data and study design. The comment of Kalman and Colker regarding nutrient analysis is also incorrect. Besides the analysis of macronutrients and isoflavones, we also calculated total cholesterol and saturated, monounsaturated, and polyunsaturated fat, as stated in the paper. Soy intake was also known because the only form of soy consumed was the one provided in the test protein (1).

Regarding the non-HDL-cholesterol values, non-HDL cholesterol is by definition any cholesterol that is not associated with HDL particles, and it corresponds to the cholesterol from all apolipoprotein B–containing lipoproteins [ie, VLDL, IDL, LDL, and lipoprotein(a)] (6). We labeled non-HDL cholesterol as VLDL + LDL cholesterol because the traditional definition of LDL entails LDL + IDL + lipoprotein(a) (7). We chose to report non-HDL cholesterol because it has been shown to be a good indicator of coronary heart disease (6).

We agree that measuring actual concentrations of LDL and VLDL cholesterol separately would provide additional useful information, especially because LDL cholesterol is used historically to determine risk of coronary heart disease (8). LDL cholesterol is also commonly determined through use of the Friedewald formula (9). However, it is well known that this formula is not accurate if triacylglycerol concentrations are >4.66 mmol/L (400 mg/dL) (10). Moreover, when triacylglycerol concentrations are between 2.3 and 4.5 mmol/L (200–400 mg/dL), LDL-cholesterol values obtained by the Friedewald formula show considerable variability as compared with those from ultracentrifugation (10). Most patients in our study fell into 1 of the 2 previous categories, so we chose not to use the Friedewald formula.

REFERENCES

1. Teixeira SR, Potter SM, Weigel R, Hannum S, Erdman JW Jr, Hasler CM. Effects of feeding 4 levels of soy protein for 3 and 6 wk on blood lipids and apolipoproteins in moderately hypercholesterolemic men. Am J Clin Nutr 2000;71:1077–84.
2. Carroll KK. Review of clinical studies on cholesterol-lowering response to soy protein. J Am Diet Assoc 1991;91:820–7.
3. Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. N Engl J Med 1995;333:276–82.
4. Kritchevsky D. Dietary protein, cholesterol and atherosclerosis: review of the early history. J Nutr 1995;125:589S–93S.
5. Food and Drug Administration. Food labeling: health claims; soy protein and coronary heart disease. Fed Regist 1999;64:57699–733.
6. Vega G, Grundy S. Does measurement of apolipoprotein B have a place in cholesterol management? Arteriosclerosis 1990;10:668–71 (editorial).
7. Belcher J, McNamara J, Grinstead G, Rifai N, Warnick G, Bachorik P. Measurement of low-density lipoprotein cholesterol concentration. In: Rifai N, Warnick G, eds. Laboratory measurement of lipids, lipoproteins and apolipoproteins. Washington, DC: AACC Press, 1994:107–24.
8. The Expert Panel. Summary of the second report of the National Cholesterol Education Program (NECP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel II). JAMA 1993;296:3015–23.
9. Friedewald W, Levy R, Frederickson D. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem 1972;18:499–502.
10. Schaefer E, McNamara J. Overview of the diagnosis and treatment of lipid disorders. In: Rifai N, Warnick G, eds. Laboratory measurement of lipids, lipoproteins and apolipoproteins. Washigton, DC: AACC Press, 1994:21–42.