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Dr. Barry said malnourished mothers in poor countries still produce healthy breast milk, though they may not be able to make enough, but are unlikely to have access to clean water for reconstituting powdered infant formula. In wealthier countries, poor women who do have access to clean water often dilute expensive formula to make it last longer, which can also cause malnutrition.

Twelve years ago, during the George W. Bush administration, the Department of Health and Human Services promoted breast-feeding in a public health campaign that suggested that failing to breast-feed would be as bad for your baby as riding a mechanical bull while pregnant. A senior scientific adviser to the Office on Women’s Health in the department at that time said that it was risky not to breast-feed, and compared not breast-feeding to smoking during pregnancy.

While some women are unable to breast-feed, cannot make enough milk, have medical conditions that prevent them from breast-feeding, or choose not to, the consensus of most mainstream medical organizations is that “breast is best” when it comes to infant nutrition and health. Breast milk provides essential nutrients as well as hormones and antibodies that protect newborns against infectious disease.

A report by the federal Agency for Healthcare Research and Quality analyzed the available evidence on breast feeding and found that breast-fed infants had significantly fewer respiratory tract infections during their first year of life, a 50 percent decrease in ear infections, and a 64 percent decrease in gastrointestinal infections. For premature infants, breast milk is considered critical because it lowers their risk of developing necrotizing enterocolitis, a dangerous condition that can destroy the wall of the intestine.

Breast-feeding is also associated with a lower risk for sudden infant death syndrome; allergies, including conditions like asthma and eczema; celiac disease and childhood inflammatory bowel disease.

Children who were breast-fed have lower rates of Type 1, or juvenile, diabetes, and of two types of leukemia. They also have lower obesity rates, though the link may be a result of higher educational and income levels among many breast-feeding mothers in the United States.

The report also noted that breast-feeding makes economic sense : Researchers who ran a cost analysis reported that if 90 percent of mothers in the United States breast-fed exclusively for six months, there would be savings of $13 billion per year.