A new study may help explain why children born to mothers who smoked during pregnancy are at increased risk of obesity. Researchers found children whose mothers smoked while pregnant have structural changes in their brains that may increase preference for fatty food.

“The fact that prenatal smoking is associated with a high risk of obesity in offspring has been known, but the potential mechanism that may lead to this risk was not fully understood,” researcher Dr. Zdenka Pausova of the Hospital for Sick Children in Toronto told HealthDay. “Our study suggests that maternal smoking may cause structural changes in the part of the brain that processes reward and may increase preference for fatty food.”

She noted that smoking in pregnancy is just one of many factors that may lead to teenage obesity.

The study included 378 teenagers, 180 of whom had mothers who smoked more than one cigarette a day during their second trimester of pregnancy.

Babies born to mothers who smoked weighed less when they were born, compared with babies whose mothers didn’t smoke. They were breast-fed for shorter periods of time, and were more likely to be heavier as teenagers, the researchers report in the Archives of General Psychiatry.

Brain scans showed that teenagers whose mothers smoked in pregnancy had a significantly lower volume in the part of the brain involved in rewards, called the amygdala. The researchers found the more fat the teens ate, the lower their amygdala volume.