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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

A Meal Enriched with Soy Isoflavones Increases Nitric Oxide-Mediated Vasodilation in Healthy Postmenopausal Women^1,2

³ Nutritional Sciences Division, School of Biomedical and Health Sciences, King's College London, London SE1 9NH, UK; ⁴ Cardiovascular Division, School of Medicine, King's College London, London SE1 7EH, UK; and ⁵ Unilever Corporate Research, Sharnbrook, Bedfordshire MK44 1LQ, UK

^* To whom correspondence should be addressed. E-mail: wendy.hall{at}kcl.ac.uk.

Evidence from infusion studies suggests that soy isoflavones influence nitric oxide-dependent vasorelaxation. It is uncertain whether orally consumed isoflavones have similar effects. Healthy postmenopausal women (n = 22) consumed 2 low-fat test meals in random order 1 wk apart, with 80 mg isoflavones (ISO) or without isoflavones (CON). Endothelium-dependent vasodilation, assessed by brachial artery flow-mediated dilatation (FMD), was measured in fasting subjects, and 4 and 6 h following the test meal, in addition to blood pressure and pulse wave analysis to derive the peripheral augmentation index (pAIx). Blood samples were taken after fasting, and 5 and 7 h following the test meal for serum isoflavone, plasma 8-isoprostane F₂, nitric oxide metabolites (NOx), glucose, and triacylglycerol analysis. Serum genistein and daidzein concentrations (geometric mean, 95% CI) reached 1.49 (1.20–1.84) µmol/L and 0.95 (0.70–1.30) µmol/L, respectively, following ISO (7 h). FMD and plasma NOx concentrations were greater following ISO compared with CON, indicating better postprandial endothelial function. FMD values (%, mean ± SD) were: CON, 5.49 ± 2.32, 4.35 ± 2.32, 4.40 ± 2.26; ISO, 5.38 ± 1.91, 5.08 ± 1.74, 6.11 ± 2.60, at baseline, 4 h, and 6 h, respectively (P < 0.01). Plasma NOx concentrations (µmol/L, mean ± SD) were: CON, 20.0 ± 5.1, 16.8 ± 5.1, 23.1 ± 6.0; ISO, 18.6 ± 6.3, 19.5 ± 5.1, 21.3 ± 10.1, at baseline, 5 h, and 7 h, respectively (P < 0.005). Treatment did not affect pAIx, blood pressure, or plasma 8-isoprostane F₂ concentrations. In conclusion, consuming an isoflavone-enriched low-fat meal acutely increases endothelium-dependent vasodilation in postmenopausal women. Regular consumption of soy isoflavones may protect against endothelial dysfunction.