“I wonder if mothers who are committed to breastfeeding make other lifestyle choices which have a positive outcome on their children’s weight – eg. More likely to walk or bike than drive; healthier food choices, etc. This was probably taken into account in the surveys, but I can’t remember all the questions.”
The study did attempt to examine some influences such as gender, economic status, place of residence, family history of asthma etc on breastfeeding rates, obesity and asthma. However personal lifestyle factors are difficult to tease out.
The SAGE study, being an epidemiological study, helps researchers identify trends and associations but does not always explain the “why” of the trends. Your question is appropriate and other lifestyle factors such as diet, activity levels, stress, may well play a role in the outcome. The exact role they play and the exact mechanism continue to be important questions that researchers are trying to answer.