Critical review of the World Health Organization's (WHO) 2007 report on 'evidence of the long-term effects of breastfeeding: systematic reviews and meta-analysis' with respect to obesity.

Obesity among children and adults has become a highly recognized public health concern and there is an increasing need to discover causes and evaluate preventative measures. One putatively causal influence on obesity is breastfeeding (BF). The World Health Organization (WHO) recently published a report (WR) on 'Evidence of the Long-Term Effects of Breastfeeding: Systematic Reviews and Meta-Analysis' and concluded 'that the evidence suggests that breastfeeding may have a small protective effect[emphasis added] on the prevalence of obesity . . . [and] the effect of breastfeeding was not likely to be due to publication bias or confounding.' Here we provide a critical overview of the WR's section on BF and obesity by addressing eight questions: Q1: Is there sufficient evidence to conclude that BF is associated with lower rates of obesity in children? Q2: Is there sufficient evidence to conclude that BF is associated with lower rates of obesity among breastfed offspring once they reach adulthood? Q3: If there are such associations, what are their magnitudes in comparison with other putatively causal factors and with respect to the potential impact on individual or population levels of obesity? Q4: Is there sufficient evidence to conclude that BF causes a reduction in risk of obesity during childhood? Q5: Is there sufficient evidence to conclude that BF does not cause a reduction in risk of obesity during childhood? Q6: Is there sufficient evidence to conclude that BF causes a long-term reduction in risk of obesity that persists into adulthood? Q7: Is there sufficient evidence to conclude that BF does not cause a long-term reduction in risk of obesity that persists into adulthood? Q8: What further research might be done to address these questions? We conclude that, while BF may have benefits beyond any putative protection against obesity, and benefits of BF most likely outweigh any harms, any statement that a strong, clear or consistent body of evidence shows that BF causally reduces the risk of overweight or obesity is unwarranted at this time.