Effect of soy protein containing isoflavones on blood lipids in moderately hypercholesterolemic adults: a randomized controlled trial
Department of Medicine, Division of Preventive and Behavioral Medicine; Department of Medicine, Division of Cardiovascular Medicine
Adult; Aged; Anticholesteremic Agents; Cholesterol; Cholesterol, HDL; Cholesterol, LDL; Dietary Supplements; Double-Blind Method; Female; Humans; Hypercholesterolemia; Isoflavones; Lipids; Male; Middle Aged; Soybean Proteins; Triglycerides
Behavioral Disciplines and Activities | Behavior and Behavior Mechanisms | Community Health and Preventive Medicine | Dietetics and Clinical Nutrition | Preventative Medicine
BACKGROUND: Dietary intake of soy protein with isoflavones may be associated with reductions in serum cholesterol.
OBJECTIVES: To compare the effects of a water-washed soy protein concentrate with a milk-protein based control on blood lipid levels in hyperlipidemic men and women.
METHODS: A randomized, double-blind, controlled clinical trial including 159 subjects. After a 3-week run-in period during which all subjects consumed a milk protein-based supplement, participants were randomized into one of two groups: a control group (continued milk protein) and an intervention group (soy protein) for a five-week period. Fasting venous blood draws for lipid measurement were obtained at baseline, towards the end of the run-in period and at the end of the intervention. Blood isoflavone concentrations were measured at the end of the study.
RESULTS: Blood lipid levels were not significantly different between groups at any point in time; and there were no significant associations between blood isoflavones and lipid levels. Significant decreases in total cholesterol (19 mg/dL), and LDL-cholesterol (11 mg/dL), were observed during the run-in period, with no further decreases in lipids during the intervention period in either group.
CONCLUSIONS: These results do not support the hypothesis that water-washed soy protein has an effect on blood lipids. Several hypotheses are discussed, highlighting the selective nature of the effect of soy consumption in the population. The cholesterol-lowering effect during the run-in period may be explained by the "regression to the mean effect" and by other factors related to study participation, mainly nutrient displacement induced by the protein supplement.
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Citation: J Am Coll Nutr. 2005 Aug;24(4):275-85.