Tianna Gaines tries to feed her year-old toddler Marianna Turner, in 2009 in Philadelphia. Introducing solid foods earlier than four months of age was associated with a six-fold higher risk of obesity at age three compared with infants who had received solids later, a new study finds. (Mel Evans/Associated Press)

Parents who think they're doing their formula-fed babies a favour by getting them started extra early on solid foods might want to think again.

A new study has found a link between obesity at age three and the introduction of solid foods before the age of four months.

"Early introduction of solid foods earlier than four months of age was associated with a six-fold higher risk of obesity when compared with infants who had received solids at four to five months of age," said Dr. Susanna Huh, a pediatric gastroenterologist at Children's Hospital Boston.

"Our findings persisted even after accounting for several other factors, including maternal income and education."

Huh is co-author of the study appearing Monday in the journal Pediatrics. She and her colleagues studied 847 children, enrolling their mothers at obstetrical offices in eastern Massachusetts when they were pregnant, administering regular questionnaires and conducting some in-person visits.

The study found the timing for introduction of solid food did not affect the chances of being obese at age three if babies were breastfed.

Huh said she believes most pediatricians counsel their patients to wait until babies are at least four months old to start solids, but a recent study in the U.S. showed that one-quarter of infants received solid food for the first time before that age.

In Canada, the document Nutrition for Healthy Term Infants, produced jointly by the Canadian Pediatric Society, Dietitians of Canada and Health Canada, cites the World Health Organization in recommending that infants "should be exclusively breastfed for the first six months of life to achieve optimal growth, development and health."

"Six-month-old infants are physiologically and developmentally ready for new foods, textures and modes of feeding," it says.

Early solids and breastfed babies

Dr. Jonathon Maguire, a pediatrician at St. Michael's Hospital and the Hospital for Sick Children in Toronto, said the main take-home message of the new study is that breastfeeding is very important.

"In children who are breastfed, the age of introduction of solids doesn't seem to matter too much, between four and six months," he said. "But in babies who are formula-fed, the age of introduction seems to matter a great deal."

He said a lot of experts in child nutrition and obesity are trying to figure out what parents can do to influence what is going to happen to their child in terms of weight.

"Parents don't want their child to be obese, yet a lot of us feel powerless on what to do to change those … health trajectories," said Maguire, a scientist who is involved in a large study on young children's health outcomes called TARget Kids.

"This is a really nice example of some of the things that parents can do, so it's basically telling us, reinforcing what we already have thought for a while, that breastfeeding is very helpful, very good for many reasons.

"And that if babies are formula-fed — and there [are] a lot of babies who have to be formula-fed for a number of reasons — but if babies are formula-fed, then delaying the introduction of solids till after four months is probably a good thing, at least in terms of obesity outcomes."

Although the study didn't look at why parents might be introducing solids early, Huh said there are a lot of myths: for instance, that feeding solids early may help the infant sleep better or that infants who are rapidly gaining weight might need more food earlier.

In addition, she noted that lower income and lower education levels are associated with earlier introduction of solid food.

Maguire noted that bottle-feeding formula can be expensive.

"Regular foods are less expensive, so there's an economic incentive as well," he said. "In terms of breastfed babies, it's cheap and it's easy, and once it's going well, it's going well. And it's really not that difficult to breastfeed, once it's initiated, for six months. It seems to me there's less incentive to start solids earlier."