Effect of infant feeding on the risk of obesity across the life course: A quantitative review of published evidence

Objective. To examine the influence of initial infant feeding on obesity in later life. Methods. A systematic review of published studies investigating the association between infant feeding and a measure of obesity was performed with Medline ( 1966 onward) and Embase ( 1980 onward) databases, supplemented with manual searches. Data extraction was conducted by 2 authors. Analyses were based on odds ratios of obesity among initially breastfed subjects, compared with formula-fed subjects, pooled with fixed-effects models. Results. Sixty-one studies reported on the relationship of infant feeding to a measure of obesity in later life; of these, 28 ( 298 900 subjects) provided odds ratio estimates. In these studies, breastfeeding was associated with a reduced risk of obesity, compared with formula feeding ( odds ratio: 0.87; 95% confidence interval [CI]: 0.85 - 0.89). The inverse association between breastfeeding and obesity was particularly strong in 11 small studies of < 500 subjects ( odds ratio: 0.43; 95% CI: 0.33 - 0.55) but was still apparent in larger studies of >= 500 subjects ( odds ratio: 0.88; 95% CI: 0.85 - 0.90). In 6 studies that adjusted for all 3 major potential confounding factors ( parental obesity, maternal smoking, and social class), the inverse association was reduced markedly ( from an odds ratio of 0.86 to 0.93) but not abolished. A sensitivity analysis examining the potential impact of the results of 33 published studies ( 12 505 subjects) that did not provide odds ratios ( mostly reporting no relationship between breastfeeding and obesity) showed little effect on the results. Conclusions. Initial breastfeeding protects against obesity in later life. However, a further review including large unpublished studies exploring the effect of confounding factors in more detail is needed.