Soy equal to cow's milk for babies, says study
The results of a new study show no difference in the long-term health effects of soy infant formula and those based on cow's milk, the researchers claim.
The study, led by Dr Brian L. Strom from the University of Pennsylvania School of Medicine, did not compare infant formula to breast milk, which is now well established as the healthiest food for babies. But it is thought to be the largest controlled study ever into the long-term effects of soy versus cow's milk formulas.
The findings are reported in today's Journal of the American Medical Association.
The researchers studied 811 adults aged 20 to 34 who had participated in controlled feeding studies between 1965 and 1978. One group of 248 had been fed soy formula during infancy (age 9 days to 16 weeks); the other group of 563 had been fed cow's milk formula.
A range of 30 measures included participants' current health, height, weight, and details of menstrual and reproductive history.
The one difference they found was that women in the soy formula group had slightly longer periods and greater discomfort, although there was no difference in the severity of menstrual flow.
"The prolongation of menstrual bleeding was small and was not accompanied by heavier bleeding," write the authors.
There is good evidence that breast milk has positive long-term health effects. It lowers the risk of adult diseases such as diabetes, asthma, and obesity.
However, some mothers are unable to breast feed, and some infants are intolerant to cow's milk.
Soy milk is one alternative, but there has been concern that its high levels of phyto-oestrogens may affect the delicate, hormone-directed process of infant development. Phyto-oestrogens are plant chemicals which act like weaker versions of the hormone estrogen. They are found in many fruits, vegetables, dried beans, peas, and whole grains.
While numerous studies suggest that eating phyto-oestrogens during adulthood can protect against a range of diseases, there has been little research on the long-term effects of consumption during infancy.
The new finding that soy during infancy is correlated with a change in menstrual patterns underlines the possibility that it may have some physiological effect. It is unknown, however, whether this has any clinical effect on health, say the researchers.
"This is the first study of its kind and as such is very important," commented pediatrician Dr Pat Tuohy, who advises the New Zealand Ministry of Health on feeding soy to infants.
Dr Tuohy said there have been some suggestions that children fed soy formula might develop thyroid problems, but previous studies had been small or limited to case reports.
Parents who had fed their children soy and were concerned by such reports should feel reassured by the JAMA study, he said.
Nevertheless, he emphasized that soy formulas should still only be considered for babies with special medical conditions. The Australian College of Pediatrics also supports this policy.
The JAMA study was sponsored by the National Institutes of Health and a grant from the Infant Formula Council. Some of the researchers disclose that they have received funding for research or speaking engagements from Nestle and Mead Johnson Nutritional.