The Right Formula?

Last Editorial Review: 1/30/2005

Soy Milk vs. Cow's Milk

WebMD Feature

Reviewed By Michael Smith

Nov. 20, 2000 -- When Lori Oliwenstein-Kluger gave birth to daughter Emily, she breastfed her for the first 10 months, supplementing with soy formula when necessary. Then Lori and her husband decided it was time to switch to a bottle full-time. But they faced a big choice: Which kind of formula would be best?

They gave cow's milk formula a try, even though they'd both had trouble with it themselves as children. As it turned out, their suspicions were right: Emily promptly came down with diarrhea. So they switched to a soy formula, and Emily did fine.

For these parents and some others, choosing between formula types is a "no-brainer" since it's based on the comfort and symptoms of their child. But for parents whose babies can tolerate either type, the decision isn't so simple.

The American Academy of Pediatrics (AAP) recommends that parents give soy formula only to infants who cannot digest cow's milk or to those whose parents wish them to follow a vegan diet. For the majority of infants, the AAP says cow's milk formula is still the next best thing to breast milk. Yet the popularity of soy formulas among U.S. parents has increased, with 1 in 4 now opting for soy, according to the academy's estimates.

With growing attention to the possible health benefits of soy products, parents may be choosing this type of formula thinking it's healthier for their babies. But the AAP says it may not be so. And while the academy doesn't claim that soy formula will lead to the development of health problems, some experts aren't so sure.

The estrogen connection

The main concern about soy formula is that it contains high levels of phytoestrogens -- estrogen-like substances found in some plants. People who are worried about soy formula fear that these substances could interfere with a child's development and even cause early puberty, thyroid problems, breast development in male children, or other difficulties. Because of these concerns, a consumer group in New Zealand tried to have soy formula removed from the market in the mid-1990s. That didn't happen, but the New Zealand Ministry of Health did issue an advisory opinion to parents in 1998 recommending cow's milk formula over soy.

The next year, the concern crossed the globe when the Canadian Health Coalition, a group of consumers and health care professionals, called on the Canadian government to restrict the use of soy formulas there. So far the restriction hasn't come to pass, but the debate continues. Today, about one in five Canadian infants uses soy formula, according to estimates from the Infant Feeding Action Coalition in Canada.

Going too far?

Some experts contend that the anti-soy campaigns have gone too far. Kenneth D.R. Setchell, PhD, a researcher and professor of pediatrics at Children's Hospital Medical Center in Cincinnati, believes the fears about soy milk causing developmental problems are unfounded. He points out that the studies that sparked the New Zealand outcry were done in animals, not people. And while soy can cause some endocrine disruptions in animals, humans metabolize soy very differently, he says.

If soy formulas caused problems, Setchell says, physicians would have noticed it by now. Soy milk has been given to infants for centuries in Asian countries, according to the AAP, and in this country since 1909.

Setchell's views are supported by British pediatrician Charles Essex, MD, who wrote in the Aug. 31, 1996, British Medical Journal that there is virtually no data on the effects of phytoestrogens on children. He also noted that pediatricians have not reported large numbers of male infants developing breasts or other female traits because of soy formula. Still, he acknowledged that the long-term effects of soy are not known.

Comparing formulas

Nutritionally speaking, soy and cow's milk formulas are similar. Both include vitamins A, D, E, and K. The main difference is in their protein and sugar make-up.

Cow's milk is processed into formula by heating and other methods that make the animal proteins in the milk more digestible. Supplemental milk sugar (lactose) is added to mimic the higher sugar content of breast milk. Finally, the fat (butterfat) is removed and replaced with vegetable oils or animal fats, which are also easier to digest.

Soy formulas, which contain plant proteins and glucose or sucrose (rather than lactose), have changed greatly since they were first introduced. In the past, they included soy flour, which led to diarrhea, excess gas, and fussiness. Today, the formulas contain a soy protein isolate, which reduces the frequency of gastrointestinal problems.

The quality of protein in cow's milk formulas is a bit better than that in soy, but neither type is as good as that in breast milk, says the AAP. And lactose-free cow's milk formulations are now available for infants that are lactose intolerant.

The bottom line

There's clear consensus among most pediatricians that breast is best. The AAP recommends breast milk for the first 12 months if possible. Short of that, it recommends cow's milk formula as a first choice and soy as an alternative for vegans. But Essex also notes that if an infant is thriving on soy formula, parents should probably leave well enough alone.

Lori Oliwenstein-Kluger says she is comfortable with her choice. Today, 3-year-old Emily is doing well, but Lori will soon revisit the formula decision -- her son is due in January. Will she give him soy milk as well? She admits to some moments of doubt, wondering if the phytoestrogens might cause some hormonal problems. But her pediatrician has helped quell those concerns, and she now plans to breastfeed as long as possible, then switch him to a soy-based formula.

And her pediatrician thinks that's a fine plan.

Kathleen Doheny is a Los Angeles journalist and a contributing editor for WebMD. She also writes for Shape, Working Woman, and Fit Pregnancy magazines and The Los Angeles Times.

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