A large study of low-income mothers has confirmed that those who are
obese before pregnancy tend to breastfeed less than slimmer mothers (Am J Clin Nutr. 2003;77:931-936).
While noting that the average difference in duration of breastfeeding
was "not large," the study's authors, from the Centers for Disease Control
and Prevention (CDC), write that the increasing prevalence of obesity and
the known benefits of breastfeeding herald the significance of the findings.
Vastag B. Obesity and Breastfeeding. JAMA. 2003;289(15):1915. doi:10.1001/jama.289.15.1915-a