A new study shows that formula-fed infants or infants who stopped breastfeeding before 4 months and started eating solid foods before 4 months of age were six times more likely to be obese by age 3 than infants who started solid foods later.

However, the timing of introducing solid foods was not linked to obesity risk among infants who were breastfed for at least four months.

Researchers say childhood obesity is the leading public health problem facing children, and these results suggest that prevention strategies starting in early infancy may be needed.

“The first few months after birth may be a critical window for the development of obesity,” researcher Susanna Y. Huh, MD

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, MPH, of Children’s Hospital Boston, and colleagues write in Pediatrics. “Parental feeding practices during early infancy, such as the timing of solid food introduction, may be one key determinant of childhood obesity.”

The study, published in Pediatrics, looked at the link between when infants started solid food (before 4 months, between 4-5 months, and at 6 months or later) and the risk of childhood obesity in 847 children. At 4 months of age, about two-thirds of the children were breastfed and one-third were formula fed.

The results showed that by age 3, 9% of the children were considered obese.

Among infants who were breastfed for at least four months, the timing of starting solids was not linked to any increase in childhood obesity risk.

But infants who were never breastfed or stopped breastfeeding before the age of 4 months and started solids before 4 months of age were 6.3 times more likely to be obese by age 3.

Researchers say this increase in obesity risk was not explained by other factors such as rapid early growth.

Experts say the results validate current recommendations to wait until infants are at least 4 months old before starting them on solid foods.

“It has always been common pediatric advice to avoid starting solid foods earlier than four months of age, and preferably actually waiting until six months of age before doing so,” Cliff Nerwen, MD, medical director of the division of general pediatrics at Cohen Children’s Medical Center of New York, says in an email. “Additionally, it further confirms the tremendous long-term nutritional value of breastfeeding during the first six months of life.”