What to know about the link between breastfeeding and BMI

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Breastfeeding infants may help them not overeat. Getty Images

When it comes to ensuring your child ends up at a healthy weight, breast really might be best for feeding them when they’re infants.

That’s the finding of a study released today that examined the relationship between infant feeding practices and weight gain during the first year of life.

The researchers found that breastfeeding was linked with a lower body mass index and also a reduced risk of weight gain considered excessive in an infant’s first year of life.

The benefits of breastfeeding on BMI of infants have been well-established, but this study is the first to find that the length of time an infant is breastfed makes a difference.

“The beneficial effect of breastfeeding is stronger with longer and more exclusive breastfeeding, meaning that any is better than none, and every feed counts,” Meghan Azad, PhD, lead author of the study and a research scientist at the Children’s Hospital Research Institute of Manitoba, told Healthline.

“I think this is a positive and important message for moms. I was surprised to find that the method of breast milk feeding matters: Our results show that feeding breast milk from a bottle is not equivalent to direct feeding at the breast (although it was still superior to feeding formula). Very few studies make this distinction — it is an important finding that raises new questions for further research,” she said.

Azad and her colleagues studied 2,553 infants between 2009 and 2012. Ninety-seven percent initiated breastfeeding, and the median duration of breastfeeding was 11 months. Seventy-four percent of infants were given solids before six months.

Babies who were partially breastfed, given some expressed breast milk, or exclusively given formula had a higher BMI at age three months than babies who were exclusively breastfed directly.

It was found that the benefits of breast milk differed between breast milk delivered directly from the breast and milk expressed and given in a bottle. Azad says this was a surprising finding.

“There are several possible reasons. First, the bioactive components of breast milk could be degraded during the routine steps between pumping and feeding breast milk — i.e., pumping, freezing, and thawing,” said Azad.

“Second, feeding at the breast might promote better self-regulation because breastfed infants learn to stop feeding when they are full, whereas bottle-fed infants, regardless of what is in the bottle, are often encouraged to empty the bottle, and do not regulate their own milk intake.”

Azad said over time this may make it more difficult for infants to regulate how much food to take in when they’re hungry.

“This could lead to poor self-regulation and higher weight gain even after weaning,” Azad explained. “Feeding at the breast also promotes mother-infant bonding, which has important health and psychosocial benefits.”

In the United States, the number of children and adolescents with obesity has tripled since the 1970s. One in three children is overweight or obese, and Azad says most of those are already overweight before entering preschool.

“It is clear that obesity prevention strategies must focus very early in life,” she said.

Dr. Joan Younger Meek, chair of the American Academy of Pediatrics’ Section on Breastfeeding, says breastfeeding can be a part of a helpful foundation for an infant’s healthy development.

“There is no question that breast milk is more beneficial to a child’s overall health and development than formula,” she said.

“The American Academy of Pediatrics and the World Health Organization unequivocally state that exclusive breastfeeding is preferred for the first 6 months of life, with continued breastfeeding after the introduction of complementary solids for at least one year (AAP), or for at least two years (WHO).”

Meek pointed out that infant formula can be a helpful alternative to breast milk, but isn’t equivalent.

“There are many protective factors, growth promoting factors, hormones, and even whole cells in human milk not found in infant formula,” she told Healthline.

Breastfeeding not only helps infants develop the ability to feed when they feel hunger and stop feeding when they are full, it can also help with cognitive development, and plays a significant role in a healthy gut as well.

“Breastfeeding promotes optimal development of the bacteria that inhabit the baby’s intestinal tract, the microbiota, which protect against infection and inflammation,” said Meek. “Breastfeeding promotes optimal cognitive development.”

Dr. Jaime Friedman, a pediatrician at the Children’s Primary Care Medical Group in California, says the decision to breastfeed or use formula is a personal decision that may be influenced by a number of factors, and that women who don’t breastfeed can take steps to ensure their child is healthy.

For moms who are unable to breastfeed, she says it’s important to not overfeed.

“It makes sense that expecting a baby to finish a bottle, regardless of contents, may lead to overfeeding compared to allowing them to decide when they are finished at the breast without knowing how much they have taken,” she said.

Friedman said new mothers can take clear steps to keep their child healthy, whether or not they decide to breastfeed.

“New mothers have enough to worry about. Many already feel sad or guilty if they are unable to breastfeed,” she said. “The important thing is to avoid overfeeding or encouraging a baby to finish a bottle if they are no longer hungry.”

Breastfeeding is associated with a healthier body composition during infancy.

This benefit was found to be stronger for infants who were exclusively breastfed for longer and was found to be weaker when milk was expressed and fed from a bottle, and weaker still in infants who were given formula.