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 said.
"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,
Contact: Phyllis Picklesimer, Media/Communications Specialist
University of Illinois at Urbana-Champaign