Early nutrition, particularly breastfeeding, may modify the risk of obesity later in life. The results of previous studies of the effects of breastfeeding on obesity have been inconsistent. Owen and colleagues performed a systematic review to determine the extent to which breastfeeding affects a person’s risk of developing obesity in later life.

The authors found 61 studies measuring weight differences in formula-fed versus breastfed infants, with 28 of these reporting unadjusted odds ratios. Overall, breastfed infants were less likely to become obese than formula-fed infants, regardless of the age at which the outcome was measured. Small studies showed stronger associations between breastfeeding and reduced risk of obesity. In the six studies in which it was possible to adjust for confounding factors, the benefit of breastfeeding was reduced from an odds ratio of 0.86 before adjustment to 0.93 after combined adjustment. The protective effect of breastfeeding over obesity was stronger and more homogenous in four studies in which initial feeding groups exclusively breastfed. The effects also were more pronounced when breastfeeding lasted two or more months. In studies that looked at associations rather than providing actual odds ratios, breastfeeding was unrelated to obesity; however, these studies tended to be small.

The authors conclude that in studies reporting quantitative estimates, breast-feeding has a consistent beneficial effect on subsequent body weight. From a pathophysiologic standpoint, breastfeeding may exert its influence by affecting adipocyte development and fat deposition, as well as modulating calorie and protein intake and insulin secretion. However, nutritional studies in infants are observational, which limits their value. Also, the effect of breastfeeding seems to be markedly attenuated when adjusting for lower socioeconomic status and maternal obesity. Publication bias favoring an effect may skew the findings. More evidence on the relationship between breastfeeding and obesity is needed.