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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
SCIENTIFIC PROGRAM
Satellite Symposium
Current Understanding of Soy and Infant Health
Isoflavone and testosterone extraction from disposable diapers: the New Zealand experience.
C.H.G. Irvine, N. Shand & S.L. Alexander
Lincoln University, NEW ZEALANDConsiderable controversy exists on the merits of feeding young human infants on soy-based formulae with three major questions as yet unanswered: 1) At what age can infants hydrolyse dietary phytoestrogens into biologically-active aglycones? 2) Does a high phytoestrogen intake alter reproductive hormone concentrations in infants? and if so 3) Does this then disturb imprinting of subsequent sexual behaviours? Our study has initially focused on developing methodology for addressing the first two questions.
Isoflavone excretion in older infants appears to fluctuate, resulting in highly variable isoflavone levels when measured in spot urine samples as is common practice. Our aim was to test the feasibility of measuring isoflavones and testosterone in urine absorbed into commercially-available disposable diapers. Urine (100 ml) from adult males having a high dietary soy intake (>1 mg/kg per day) was poured into each of four diapers or retained in a plastic jar (control) and held at 4C overnight. Diapers were then soaked for 16h at 20C in 300 ml distilled water (+0.02% ascorbate, 0.02% sodium azide). Liquid was expressed by squeezing and urine dilution assessed by creatinine assay.
Steroid or isoflavone conjugates were extracted onto SepPaks, eluted, then cleaved by enzymatic hydrolysis (Patella vulgata). Isoflavones or testosterone were assayed using hplc separation with spectrophotometric detection or radioimmunoassay, respectively. Mean (+ SEM) recoveries (as a % of the control value) were 97+3% (genistein), 72+8% (daidzein) and 111+4% (testosterone).
This sampling method enables easy collection of pooled urine samples and is completely noninvasive, making large-scale home studies of normal healthy infants feasible. We have commenced such a study together with the Plunket Society, New Zealand's unique programme in which infants are monitored by regular home visits by paediatric nurses. However, recruiting soy-fed infants is proving difficult since the use of soy formula in New Zealand is declining. Over the last year, soy's share of formula sales fell by one third, which is probably due to repeated media exposure of concerns that feeding soy formulae is harmful to infant.
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