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ARS Home » Southeast Area » Little Rock, Arkansas » Microbiome and Metabolism Research Unit » Research » Publications at this Location » Publication #208771
Title: Infants fed soy formula appear to maintain steady-state isoflavone concentrations

Author
item Gilchrist, Janet
item BADGER, THOMAS - ACNC/UAMS
item GU, LIWEI - ACNC/UAMS

Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 2/7/2007
Publication Date: 4/28/2007
Citation: Gilchrist, J.M., Badger, T.M., Gu, L. 2007. Infants fed soy formula appear to maintain steady-state isoflavone concentrations [abstract]. The FASEB Journal. 21(5):A369.

Interpretive Summary: We studied the blood levels of isoflavones ("estrogen-like" substances found in soy-foods) in 3-month-old infants (40 boys, 31 girls). All infants studied had been fed only soy-based infant formula since at least 2 months of age. Infants came to our Center after not having any formula for at least four hours. We drew blood once from each infant at one of five time points: before having formula, 1/2 hour, 1 1/2 hours, 2 1/2 hours, or 3 1/2 hours after having a bottle of soy formula. The blood was analyzed for isoflavones. The levels of isoflavones in infants' blood did not change over time. The major isoflavones present in infants' blood were genistein and daidzein. Infants' blood values of genistein and daidzein were nearly the same as levels found in the blood of adults who eat a lot of soy-based foods. Only one infant out of the 71 had any equol in their blood. Several other isoflavones break-down products, DHD, DHG, and O-DMA, were found in the blood of 3, 4, and 12 infants, respectively. The levels of isoflavones in infants’ blood did not differ based on sex or body weight. These data suggest that infants on soy-based infant formula have steady-state levels of isoflavones in their blood. These levels are in the range known to have effects on metabolism. Some infants had break-down products in their blood, so infants at this age are able to metabolize isoflavones. Future studies will determine if these levels of isoflavones have effects on development and health of children or whether there may be health issues that become apparent when they are adults.

Technical Abstract: We studied the isoflavone pharmacokinetics of 71 healthy 3-mounth old infants (40 boys) who were exclusively fed soy-based infant formula (SF) for at least 1 mounth. Each study began after a 4-hr fast. Blood was drawn once from each infant at one of five time points: prior to feeding, 0.5, 1.5, 2.5, or 3.5 hrs after feeding. Plasma isoflavones were enzymatically hydrolyzed to yield aglycones, extracted using ethyl acetate, and quantitated using LC-MS. Genistein and diadzein accounted for >95% of total plasma isoflavones. Plasma values of genistein (2.71 plus/minus 1.17 umol/L) and daidzein (0.98 plus/minus 0.39) are similar to those reported for adults with high soy food intake. Only one infant had detectable plasma equol (1.11 umol/L). The metabolites DHD, DHG, and O-DMA were present in plasma of 3, 4, and 12 infants, respectively. Plasma isoflavones did not differ across time and were not correlated with body weight or sex. Amoung some infants, we observed metabolites produced from enzymes thought to be deficient in early life. Infants on SF appear to have steady-state levels of plasma isoflavones in concentrations expected to have biological effects. These preliminary data suggest that future studes of infants fed SF can use plasma obtained at any time point to assess circulating isoflavones.