A systematic review and meta-analysis of prospective cohort studies evaluating infant risk factors for childhood obesity found that breastfeeding was associated with a lower risk of obesity.1 The authors identified 10 trials (primarily from the United States and Europe) with more than 76,000 infants that compared the effect of some breastfeeding in the first year to no breastfeeding. Follow-up ranged from 2 to 14 years (median 6 years).
Having ever breastfed decreased the odds of future overweight (BMI >85th percentile) or obesity (BMI >95th percentile) by 15% (adjusted odds ratio [AOR]=0.85; 95% confidence interval [CI], 0.74-0.99).
Subsequent studies suggest increased risk with formula feeding
Three large, prospective, longitudinal cohort studies have been published since the meta-analysis. One, which followed 43,367 term infants in Japan, found that formula feeding before 6 months was associated with increased risk of obesity compared with continuous breastfeeding for 6 months.2 Researchers evaluated weight at 7 years and adjusted for child and maternal factors associated with weight gain (AOR for obesity, formula-fed infants=1.8; 95% CI, 1.3-2.6).
A similar prospective longitudinal cohort study of 2868 infants in Australia analyzed maternal breastfeeding diaries and followed children’s weight to age 20 years.3 Introducing a milk other than breast milk before 6 months of age was linked to increased risk of obesity at age 20 (odds ratio [OR]=1.5; 95% CI, 1.1-1.9).
Finally, in a prospective cohort of 568 children in India, 17% of children who breastfed for fewer than 6 months were above the 90th percentile for weight at age 5 years, compared with 10% of children who were breastfed for at least 18 months.4 The result didn’t reach statistical significance, however (P=.08).
Interventions that increase breastfeeding don’t seem to have an impact
An RCT of an intervention to promote breastfeeding didn’t find any effect on subsequent obesity rates. Researchers in Belarus randomized 17,046 mother-infant pairs to breastfeeding promotion, modeled on the UNICEF Baby-Friendly Hospital Initiative, or usual care. The intervention increased the prevalence of exclusive breastfeeding (at 3 months, 43% vs 6%; at 6 months, 7% vs 0.6%; P values not given).
When researchers evaluated 13,879 children at 11 or 12 years by intention-to-treat analysis, however, they found no difference in mean BMI between the children whose mothers received the intervention and those whose mothers didn’t (BMI difference=0.16; 95% CI, -0.02 to 0.35).5
Introduction of solid foods: Later is better
A systematic review investigated the association between the timing of introducing complementary (solid) foods and childhood obesity in 23 primarily cross-sectional and cohort studies (17 from the United States, Canada, and Europe) with more than 33,000 patients. Follow-up ranged from 4 to 19 years.