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Letters to the Editor |
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
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