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Setchell KD, Zimmer-Nechemias L, Cai J, Heubi JE.
Lancet 1997 Jul 5 350:9070 23-7.
Abstract
BACKGROUND: The isoflavones genistein, daidzein, and their
glycosides, found in high concentrations in soybeans and soy-protein
foods, may have beneficial effects in the prevention or treatment
of many hormone-dependent diseases. Because these bioactive phyto-oestrogens
possess a wide range of hormonal and non-hormonal activities, it
has been suggested that adverse effects may occur in infants fed
soy-based formulas.
METHODS: To evaluate the extent of infant exposure to phyto-oestrogens
from soy formula, the isoflavone composition of 25 randomly selected
samples from five major brands of commercially available soy-based
infant formulas were analysed, and the plasma concentrations of
genistein and daidzein, and the intestinally derived metabolite,
equol, were compared in 4-month-old infants fed exclusively soy-based
infant formula (n = 7), cow-milk formula (n = 7), or human breast-milk
(n = 7). FINDINGS: All of the soy formulas contained mainly glycosides
of genistein and daidzein, and the total isoflavone content was
similar among the five formulas analysed and was related to the
proportion of soy isolate used in their manufacture. From the concentrations
of isoflavones in these formulas (means 32-47 micrograms/mL), the
typical daily volume of milk consumed, and average bodyweight, a
4-month-old infant fed soy formula would be exposed to 28-47 per
day, or about 4.5-8.0 mg/kg bodyweight per day, of total isoflavones.
Mean (SD) plasma concentrations of genistein and daidzein in the
seven infants fed soy-based formulas were 684 (443) ng/mL and 295
(60) ng/mL, respectively, which was significantly greater (p <
0.05) than in the infants fed either cow-milk formulas (3.2 [0.7]
and 2.1 [0.3] ng/mL), or human breast-milk (2.8 [0.7] and 1.4 [0.1]
ng/mL), and an order of magnitude higher per bodyweight than typical
plasma concentrations of adults consuming soy foods.
INTERPRETATION: The daily exposure of infants to isoflavones in
soy infant-formulas is 6-11 fold higher on a bodyweight basis than
the dose that has hormonal effects in adults consuming soy foods.
Circulating concentrations of isoflavones in the seven infants fed
soy-based formula were 13000-22000 times higher than plasma oestradiol
concentrations in early life, and may be sufficient to exert biological
effects, whereas the contribution of isoflavones from breast-milk
and cow-milk is negligible.
Setchell KD, Zimmer-Nechemias L, Cai J, Heubi JE.
Am J Clin Nutr 1998 Dec 68:6 Suppl 1453S-1461S.
Abstract
Soy-based infant formulas have been in use for >30 y.
These formulas are manufactured from soy protein isolates and contain
significant amounts of phytoestrogens of the isoflavone class. As
determined by HPLC, the isoflavone compositions of commercially
available formulas are similar qualitatively and quantitatively
and are consistent with the isoflavone composition of soy protein
isolates. Genistein, found predominantly in the form of glycosidic
conjugates, accounts for >65% of the isoflavones in soy-based
formulas. Total isoflavone concentrations of soy-based formulas
prepared for infant feeding range from 32 to 47 mg/L, whereas isoflavone
concentrations in human breast milk are only 5.6 +/- 4.4 microg/L
(mean +/- SD, n = 9). Infants fed soy-based formulas are therefore
exposed to 22-45 mg isoflavones/d (6-11 mg x kg body wt(-1) x d(-1)),
whereas the intake of these phytoestrogens from human milk is negligible
(<0.01 mg/d). The metabolic fate of isoflavones from soy-based
infant formula is described. Plasma isoflavone concentrations reported
previously for 4-mo-old infants fed soy-based formula were 654-1775
microg/L (mean: 979.7 microg/L: Lancet 1997:350;23-7), significantly
higher than plasma concentrations of infants fed either cow-milk
formula (mean +/- SD: 9.4 +/- 1.2 microg/L) or human breast milk
(4.7 +/- 1.3 microg/L). The high steady state plasma concentration
of isoflavones in infants fed soy-based formula is explained by
reduced intestinal biotransformation, as evidenced by low or undetectable
concentrations of equol and other metabolites, and is maintained
by constant daily exposure from frequent feeding. Isoflavones circulate
at concentrations that are 13,000-22,000-fold higher than plasma
estradiol concentrations in early life. Exposure to these phytoestrogens
early in life may have long-term health benefits for hormone-dependent
diseases.
Author Address
Clinical Mass Spectrometry Center, Children's Hospital
Medical Center, Cincinnati, OH 45229, USA.
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