Surgeon General Regina Benjamin has issued a "call to action" on breast-feeding, urging families, communities, and employers to support women in their efforts to breast-feed. The American Academy of Pediatrics says women should breast-feed exclusively until a baby is six months old. But only 13 percent of women make that target.
Public health experts have pushed breast-feeding as being better for babies because the nutritional balance in breast milk is ideal for infant humans. Breast milk has also been touted for giving newborns immunity from disease, because they ingest antibodies their mothers have produced to fight off germs.
But new research investigating the makeup of human breast milk is uncovering surprises. A mother probably wouldn't say she favors her sons over her daughters, but her body may be doing that from the moment she first holds them to her breast. A mother's body creates different milk for baby boys than it does for baby girls—the boy milk has much more fat and protein, which presumably helps them grow bigger, faster.
The fact that boys get a different "formula" than girls is just one surprise. Indeed, a recent study by researchers at the Telethon Institute for Child Health Research in Perth, Australia, found that boys who were breast-fed for at least six months did better in school at age 10 than did boys who weren't breast-fed. The study was published online in Pediatrics. (The same effect was not seen in girls.)
Another surprise is that human milk contains carbohydrates (oligosaccharides) that don't feed the baby. Instead, they feed good gut bacteria, which help protect a baby against diarrhea. Calito Lebrilla, a chemist at the University of California-Davis, has found that each mother produces her own recipe for human milk oligosaccharides, which means each baby will have tailor-made gut bacteria. No one knows why.
The story gets stranger. Mother's milk also delivers microbes from the mother's intestines to her baby. These lactic acid bacteria travel probably piggyback on white blood cells to reach the mother's mammary glands. These good bacteria attack bad bacteria by pumping out hydrogen peroxide and other compounds that are toxic to other bacteria. Researchers have also found suggestions that the bacteria in breast milk can influence which genes are active in a baby's gut, perhaps impacting the child's digestion.
So by breast-feeding a mother not only gives her baby nutrition, but gives that child important information about the world: what the mother is eating, the environment surrounding her, and even what dangerous germs lie in wait.
Intriguing as this science is, it doesn't help parents answer the big question: Is breast milk always better than formula? The evidence on that varies, according to a recent Nature review on the state of breast milk research. But there's good evidence that breast milk gives babies a boost in the first year of life. It protects pre-term infants from life-threatening gut infections, and reduces the risk of diarrhea and ear infections in full-term babies.
But as children grow, the influence of breast milk becomes less clear. Several studies, including the recent Pediatrics study, have found cognitive benefits. Earlier this decade, researchers in Belarus found a boost in IQ of almost 6 points for formerly breast-fed children at age 6.
Some studies have found that breast-fed babies are less likely to be obese once they reach school age, but that may be because standard infant formulas are packed with more protein than breast milk is. A European study that tested high-protein formula against a low-protein variation more similar to human milk found that children fed the low-protein formula gained no more weight than the breast-fed children did.
Breast-feeding has become politicized in recent years, with both breast-feeding advocates and formula manufacturers touting special benefits for their product. The science so far doesn't end that debate. But it does make the case for subtle yet substantial benefits for mother's milk.