Children born by Cesarean section are no more likely to become obese than those who are born vaginally, according to a Brazilian study.

Past research from Brazil had found a link between excessive weight and C-sections, leading some scientists to suggest that not being exposed to bacteria from the birth canal could make children fatter. But the latest findings - published in the American Journal of Clinical Nutrition - suggest this doesn't appear to be the case.

"We thought from the beginning that probably what happened with the previous study is that they didn't adjust for all of the confounders," says Fernando Barros of the Catholic University of Pelotas, who worked on the study, referring to such factors as the mother's height and weight.

"The really simple explanation would be that more obese women require more Cesarean sections than lean women ... and it's really not the C-section itself," says David Ludwig, director of the Optimal Weight for Life Clinic at Children's Hospital, Boston, who was not involved in the study.

He says that things, such as a pregnant woman's diet and smoking habits, and whether or not she has diabetes, might influence a developing fetus.