March 17, 2006 -- There is not enough scientific data to determine whether or not soy formula consumed by millions of infants poses a health risk, a government panel concluded Friday.
Experts say they have little concern that an estrogen-like substance in soy -- known as genistein -- poses a developmental risk to infants who consume it or whose parents consumed it in soy-based foods.
Still, very few studies have looked at the long-term health effects of soy formula, which is used to feed an estimated 25% of all U.S. infants, the panel says.
Soy has raised concerns not only because of its exploding consumption by U.S. infants and adults but also because studies have shown that genistein can interfere with hormonal function in rats and their offspring.
A variety of toxic effects, including stunted growth, sexual organ abnormalities, and decreased fertilization, have all been observed in laboratory animals. All of the effects appear to be caused by genistein's ability to mimic the effects of natural estrogen. Some researchers also suspect soy of playing a role in reduced breast cancer rates in Japan, where soy consumption is very high.
The committee says it had "negligible" concern that usual intakes of genistein cause adverse health effects in newborns and infants who consume soy formula, though one expert -- Ruth Etze, MD -- dissented from the conclusion. Etzel, a pediatrician at the Alaska Native Medical Center in Anchorage, could not be reached for comment.
Human infants consume much lower genistein doses than laboratory animals, and most of the chemical is not absorbed into the human bloodstream, says Karl Rozman, PhD, a University of Kansas toxicologist who led NIH panel.
But at the same time, few studies have looked at soy's effects in a controlled way, he explains.
More Study Needed
"That means there are studies there, but they are not allowing us to come to a firm conclusion one way or another. But it also means that we do not see a problem," says Rozman.
One study pegged infant formula feeding as a risk factor for premature breast development in girls. Experts called for better research to determine if that and other potential health effects are real.
"Another case-control study to examine premature breast development in females following exposure to soy infant formula is needed," the committee concludes.
Panelist Jatinder Mhatia, MD, says soy formula has not shown "a blip on the radar screen" in terms of ill health consequences, despite use by an estimated 40 million total infants.
But Mhatia also says parents are up to 10 times more likely to give their infants soy formula in the U.S. than in Britain. Some countries, including Israel, have restricted formula use to prescription-only status for infants who cannot consume milk. But American doctors are quick to recommend formula for fussy infants, which parents are heavily encouraged by advertising to use, he says.
"Only in our country are we using [soy] in a free-for-all," Mhatia, a pediatrician at the Medical College of Georgia, tells WebMD. "Soy has a specific indication, and we tend to use and abuse in America."
"Why should you use soy unless there's an indication?" he says.