No, definitely not just formula. It starts with the flora you get from your mother (which is affected by her formula/vax/antibx/hormonal-contraception/etc. status), is affected by vaginal or surgical birth, who first holds the baby, how he is fed (even ONE bottle of formula can disrupt the new baby's flora dramatically), vaccination, antiobiotcs, grains, and sugar.
I apologize; I don't think the abstract went into the conclusions. Here's a media report on the study. http://news.yahoo.com/s/hsn/20080308...redictsobesity
According to the overview, the researchers suggest that the impact on gut flora may be a part of why breastfeeding is associated with decreased obesity risk.