| Summary: | Background: The value of soy, as an effective component of a cholesterol lowering diet, is currently questioned due to smaller lipid reductions than previously reported for the currently approved US FDA health claim for soy. Nevertheless, intrinsic and extrinsic factors may exist that influence the effectiveness of soy, but little research has been done in this area. Such factors include the soy isoflavone content, dietary components that alter colonic fermentation and the colon’s ability to biotransform isoflavones (i.e. equol status).
Objective: To determine if specific factors, such as dose of soy isoflavones and those that alter colonic fermentation, influence the hypocholesterolemic effect of soy. Furthermore, whether cholesterol reductions differ depending on the interindividual variation in isoflavone biotransformation (i.e. equol status), when soy is consumed under different dietary conditions (i.e. with specific factors).
Methods: 85 men and postmenopausal women (42M, 43F) with hyperlipidemia participated in one of three substudies where soy foods, containing 30-52g/d of soy protein, were provided over a one-month period under the following conditions: 1) high-normal (73mg/d) or low (10mg/d) soy isoflavones (N=41); 2) with or without a prebiotic (10g/d polyfructans) to increase colonic fermentation (N=22); or 3) with a reduced carbohydrate diet (26% of calories) to decrease colonic fermentation (N=22).
Results: Unmodified soy foods significantly reduced LDL-C by 5.1%±2.0% (P=0.016). LDL-C reductions were not altered with increased soy isoflavone content nor were the effects dampened with reduced carbohydrate. However, coingestion of soy with a prebiotic improved the cholesterol lowering effect of soy. Equol producers (N=30) showed a relative increase of 5.3±2.5% in HDL-C (P=0.035) after soy compared to nonproducers (N=55), but no significant differences were observed for LDL-C or other lipids. Equol excretion was increased with increased soy isoflavone content, but not with the addition of a prebiotic.
Conclusion: The effectiveness of soy, as a cholesterol lowering food, may be improved with the addition of prebiotics, but not with decreased carbohydrate or increased isoflavones. Equol status appears to alter the HDL-C, but not the LDL-C response. These data support the continued use of soy foods as part of the dietary approach to coronary heart disease risk reduction.
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