By age six, children of overweight mothers are fifteen times more likely to be obese than children of lean mothers, according to University of Pennsylvania researchers reporting in the American Journal of Clinical Nutrition.

.The researchers concluded that their study showed the strength of genetic influences on obesity, and suggested that efforts to prevent obesity should focus on such children at risk, preferably by four years of age.

Researchers followed 70 children over a six-year period at Children's Hospital; of that number, 33 had overweight mothers and 37 had lean mothers. During the first two years of age, weight and body composition differed little between the two groups. But the high-risk group (children whose mothers were overweight) had greater overall weight by age four, and both greater weight and more body fat by age six.

"We found dramatic increases in body fat between ages three and six," said Dr. Robert I. Berkowitz, chair of Child and Adolescent Psychiatry at The Children's Hospital of Philadelphia. "This suggests that some genes controlling body weight may become active during this period."

Among the low-risk group, only one of the 37 children was overweight, suggesting that genetic influences can protect against obesity as well as predisposing to it.

The fact that increased body weight at age four is followed by increased body fat at age six indicates that prevention efforts should begin by age four for overweight children of overweight mothers. "It is not necessary to wait to see increased body fat by age six if the child is already overweight," Dr. Berkowitz said.

"There appears to be an interaction between the genes that control body weight and environmental factors such as increased intake of sweets and fats, as well as inactivity, all of which are associated with the development of childhood obesity," noted Dr. Albert J. Stunkard of the University of Pennsylvania School of Medicine, a co-author of the study.

Other sources: American Journal of Clinical Nutrition