Two studies by University of Illinois food
science and human nutrition professor Sharon Donovan show
that the soy isoflavone genistein, in amounts present in commercial
soy infant formulas, may inhibit intestinal cell growth in
babies. So what are we to think about soy in a baby's diet?
Donovan said it's an important question to ask because almost
25 percent of formula-fed babies in the United States consume
soy formula. Although babies on soy formula appear to grow
normally, these formulas contain very high concentrations
of genistein, from 32 to 45 milligrams, which is higher than
the amount found to affect menstrual cycles in women, she
"I'm struck by the fact that these babies are receiving
isoflavones at such high concentrations," Donovan said.
"Formula is the sole source of nutrition for these infants
for the first four to six months of life, when so many important
organ systems are developing."
In the first study, published in the Journal of Nutrition
in June 2004, Donovan treated intestinal cells in culture
with genistein in the amount present in soy infant formula
and found that the cells "basically stopped proliferating."
However, actions seen in cells in culture may not be seen
in infants, Donovan said.
In a second study, she fed one group of newborn piglets a
cow's milk-based formula, while feeding other piglets formula
supplemented with genistein at the level found in soy formula.
This study will be published in the February 2005 issue of
Pediatric Research, but an electronic version was released
on line on Dec. 7.
Newborn pigs are an excellent model for human infants because
they have a similar metabolism and physiology, Donovan said.
In the piglets fed genistein, the number of proliferating
cells in the intestine was 50 percent lower than piglets fed
the cow's milk formula alone. Concentrations of genistein
in the piglets' blood were similar to those of babies fed
soy formula, so these data may be applicable to human infants,
the researcher said.
No differences in the activities of digestive enzymes or
uptake of nutrients were observed, which suggests that genistein
had little effect on mature intestinal cells that were no
Although these data are the first to show that genistein
is bioactive in the neonatal intestine, Donovan said these
results do not mean soy formulas should not be fed to babies.
"Clinical data suggest that soy formulas are safe,"
she said, "but even though they appear to be safe, they
may not be without effect."
So far, Donovan has studied genistein alone, but soy formulas
contain other soy isoflavones that likely affect genistein's
actions in the intestine. The researcher plans to study those
interactions. "Soy isoflavones may have both positive
and negative effects that need to be better understood,"
Donovan pointed to recent research that showed adding long-chain
polyunsaturated fatty acids to infant formula improves brain
and retinal development and even IQ scores. Recent research
has also shown that adding nucleotides to baby formula causes
babies to react better to vaccinations and make more antibodies,
"And although that research showed differences that
were measurable, the babies fed formula with added fatty acids
or nucleotides appeared to grow the same as other babies do,"
she said. "So I don't think you can use growth as the
sole parameter for normal development."
An-Chian Chen contributed to the cell-culture study. Other
researchers contributing to the piglet study were An-Chian
Chen, a doctoral student in nutritional sciences; Mark A.
Berhow, an adjunct professor of biochemistry in the UI department
of crop sciences and researcher for the USDA-ARS Bioactive
Agents Research Unit in Peoria, Ill.; and Kelly A. Tappenden,
professor of food science.
Both studies were funded by the Illinois Council on Food
and Agricultural Research and the USDA.