Obesity in young people is a major and growing health concern.
Scientists say that exposure to a mother's cigarette smoke while in the womb increases a child's risk for obesity.
A study in the Archives of General Psychiatry looked at 378 adolescents from ages 13 to 19.
Some had been exposed to maternal smoking, some had not.
Those who were exposed eventually had higher body weight and higher total body fat.
The exposed teens also showed a lower volume in a part of the Brain associated with limiting fat intake.
This may increase a dietary preference for fat, contributing to obesity.