The effect on the blood lipid profile of soy foods combined with a prebiotic: a randomized controlled trial.

The value of soy protein as part of the cholesterol-lowering diet has been questioned by recent studies. The apparent lack of effect may relate to the absence of dietary factors that increase colonic fermentation and potentiate the cholesterol-lowering effect of soy. Therefore, unabsorbable carbohydrates (prebiotics) were added to the diet with the aim of increasing colonic fermentation and so potentially increasing the hypocholesterolemic effect of soy. Twenty-three hyperlipidemic adults (11 male, 12 female; 58 +/- 7 years old; low-density lipoprotein cholesterol [LDL-C], 4.18 +/- 0.58 mmol/L) completed three 4-week diet intervention phases-a low-fat dairy diet and 10 g/d prebiotic (oligofructose-enriched inulin, a fermentable carbohydrate), a soy food-containing diet (30 g/d soy protein, 61 mg/d isoflavones from soy foods) and 10 g/d placebo (maltodextrin), and a soy food-containing diet with 10 g/d prebiotic--in a randomized controlled crossover study. Intake of soy plus prebiotic resulted in greater reductions in LDL-C (-0.18 +/- 0.07 mmol/L, P = .042) and in ratio of LDL-C to high-density lipoprotein cholesterol (-0.28 +/- 0.11, P = .041) compared with prebiotic. In addition, high-density lipoprotein cholesterol was significantly increased on soy plus prebiotic compared with prebiotic (0.06 +/- 0.02 mmol/L, P = .029). Differences in bifidobacteria, total anaerobes, aerobes, and breath hydrogen did not reach significance. Soy foods in conjunction with a prebiotic resulted in significant improvements in the lipid profile, not seen when either prebiotic or soy alone was taken. Coingestion of a prebiotic may potentiate the effectiveness of soy foods as part of the dietary strategy to lower serum cholesterol.