Early ReportExposure of infants to phyto-oestrogens from soy-based infant formula
Introduction
More than a decade after attention was first drawn to the levels of phyto-oestrogens in soy infant-formulas,1, 2 concerns are being expressed about the possibility of hormonal effects from exposure of infants to phyto-oestrogens from soy-based infant formulas.3 These concerns have prompted at least one government agency to issue statements and recommendations about the use of soy-based infant formulas in early life.4
The phyto-oestrogens in all soy-protein foods belong to the isoflavone class.1 With few exceptions all soy-protein products and soybeans are rich in isoflavones.5, 6 Variation in amount of isoflavones in different soy foods is accounted for mainly by the differences in industrial processing of the soybean, and the type and extent of incorporation of the soy protein into the food matrix.5 Isoflavones when ingested are metabolised extensively in the intestinal tract, absorbed, transported to the liver, and undergo enterohepatic recycling.1, 7, 8 Intestinal bacterial glucosidases cleave the sugar moieties and release the biologically active isoflavones, daidzein and genistein, and in the adult these can be further biotransformed by bacteria to the specific metabolites, equol,9 desmethylangolensin, and p-ethylphenol.10 All of these phyto-oestrogens are then eliminated, mainly by the kidney, and therefore share the physiological features and behaviour of endogenous oestrogens.7
In addition to acting as oestrogen mimics,7, 8 isoflavones have important non-hormonal activities. Genistein, for example, is a potent inhibitor of tyrosine kinases11 and interferes with cell signal-transduction pathways.12 The ingestion of high concentrations of phyto-oestrogens has adversely affected reproduction in several animal species,13, 14 and in premenopausal women daily ingestion of soy protein lengthens the menstrual cycle and suppresses the usual midcycle surge in pituitary gonadotropins,15 effects that epidemiological evidence suggests are beneficial in decreasing risk of breast cancer. The hypocholesterolaemic action of soy protein is well established and anticancer actions of soy isoflavones have been shown in in-vitro studies and in several classic animal models of chemically-induced breast cancer.7, 8
Although urinary analyses have indicated that isoflavones are absorbed by the infant fed soy-based infant formula, data on the composition of phyto-oestrogens in infant formulas are scant and the level of exposure of the infant fed soy-based formula to phyto-oestrogens is uncertain. We now describe a comprehensive analysis of the isoflavone composition of randomly selected samples of five different brands of commercially available soy-based infant formulas and a comparison of the plasma concentrations of isoflavones in 4-month-old infants fed soy infant-formula, cow-milk formula, and human breast-milk.
Section snippets
Phyto-oestrogen analysis of soy-based infant formulas
Five samples each of five of the major commercial brands of soy-based infant formulas were purchased from three stores in the Cincinnati area. The brands were: Nursoy powdered formula (Wyeth Laboratories, Philadelphia, Pennsylvania), Isomil powdered formula (Ross Products Division Abbott Laboratories, Columbus, Ohio), Isomil “Ready to Feed” liquid formula (Ross Products Division Abbott Laboratories, Columbus, Ohio), Alsoy liquid formula concentrate (Carnation Nutritional Products Division,
Isoflavone composition of soy-based infant formulas
A typical HPLC profile of the phenolic fraction of soy-based infant formula consists of a complex pattern of peaks with absorbance at 260 nm that were identified on the basis of retention index and mass spectrometry to be conjugated and unconjugated isoflavones.5 The predominant isoflavones identified in all of the soy-based formulas were the β-glycosides, genistin and daidzin, and the 6-“O”-malonyglycosides and 6-“O”-acetylglycosides of genistein and daidzein. Glycitin was also found in
Discussion
Since most brands of soy infant-formulas are prepared from soy isolates, the total isoflavone content should be similar among formulas, and related to the proportion of soy isolate incorporated. All five soy-based formulas analysed contained considerable amounts of isoflavones, and these were mostly glycosidic conjugates of daidzein and especially of genistein. Unconjugated isoflavones accounted for only 3–6% of the total. This composition is consistent with the reported findings for soy
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