The role of breastfeeding in obesity.

Most studies examining the effects of breastfeeding on later obesity have found an insignificant effect. Breastfeeding was positively associated with later body fatness in two studies. A protective effect of breastfeeding on childhood obesity was seen in four studies. An effect of breastfeeding on later obesity, if any, is probably weaker than genetic and other environmental factors. Also, an observed association between breastfeeding and later obesity does not prove causality. Controlling for confounders in an attempt to minimize the effects of differences between breastfeeding and formula-feeding mothers was done to a varying extent across studies. In several of the later studies, adjustment for confounders obliterated the effect of breastfeeding. Whether all the pertinent confounding factors have been measured and whether the differences between mothers who chose to breastfeed and mothers who chose to formula-feed have been controlled for adequately are always questionable. The dose response observed with the duration of breastfeeding is consistent with a causal association, but confounders associated with breastfeeding also may covary in a graded response. Although a highly provocative concept, the protective effect of breastfeeding on later obesity remains controversial.