Isoflavones in breastfed infants after mothers consume soy1–3

Background: The bioavailability of isoflavones in children after soy exposure is uncertain. Objective: We aimed to compare isoflavone patterns in infants exposed to isoflavone-containing breast milk (BF), in tofu-fed (TF) infants, and in mothers consuming a soy beverage. Design: Eighteen nursing mothers who were not feeding soy foods to their infants consumed one daily serving of a soy protein beverage for 2–4 d and collected their own milk and urine and infant urine. Plasma was collected from infants if venous blood draws were or-dered by pediatricians. Blood and urine were collected from addi-tional children after they consumed tofu. Isoflavones were measured by liquid chromatography–mass spectrometry. Results: In 7 subjects, isoflavone values increased significantly from baseline after mothers ate soy: in maternal urine (x SEM) from 18.4 13.0 to 135.1 26.0 nmol/mg creatinine, in breast milk from 5.1 2.2 to 70.7 19.2 nmol/L, and in infant urine from 29.8 11.6 to 111.6 18.9 nmol/mg creatinine. The mean isofla-vone concentration in plasma obtained from 11 BF infants was 19.7 13.2 nmol/L. TF infants had much higher mean isoflavone values (urine, 229 129 nmol/mg creatinine; plasma, 1049 403 nmol/L). Statistically significant correlations were observed be-tween the types of fluids investigated within mothers, between moth-ers and infants, and within infants. Urinary isoflavone excretion per hour adjusted for dose per body weight was 81 % lower for BF infants and 24 % higher for TF infants than for their mothers after eating soy. Conclusions: More isoflavones appear in children than in adults after adjustment for isoflavone intake. Systemic isoflavone exposure in infants can be determined by urinary analysis. Am J Clin Nut