Overweight 4-year-olds? It’s a common problem these days. Childhood obesity (search) is showing up at early ages — and genetics seem to play a key role, researchers say.

By age 6, children are15 times more likely to be obese if their mothers are overweight, new research shows.

The study indicates efforts to prevent childhood obesity should focus on these kids — preferably by 4 years of age.

“Some kids clearly become overweight by 4 years old … and they tend to be the children of overweight mothers,” says researcher Robert I. Berkowitz, MD, executive director of the Behavioral Health Center at the Children’s Hospital of Philadelphia. His study appears in the latest issue of the American Journal of Clinical Nutrition.

“It’s an early signal to be concerned…to help these children,” Berkowitz tells WebMD. “There’s no reason to wait for body fat to appear on these kids before intervening,” he writes.

It’s a call to action for pediatricians, says Robert Kramer, MD, a pediatric gastroenterologist and nutritionist at the Miller School of Medicine at University of Miami. He conducted his own study of preschool children in the Miami area — finding that 34 percent were overweight or obese.

“Pediatricians measure a child’s BMI, or they should be, at all well-child visits,” Kramer tells WebMD. “They should be identifying those children as having high risk for developing obesity as an adult. Studies like this show that even before children show signs of obesity, if they have maternal risk, they should get intervention.” BMI (body mass index) is an indicator of body fat.

Childhood Obesity in Toddlers Begins With Moms

With the epidemic of childhood obesity, both genetic vulnerability and environment are under the microscope. Researchers want to know: Who becomes obese? At what age does obesity begin?

Few long-term studies have examined these factors. However, two reports have identified the parents or overweight mothers specifically as key factors. Those findings prompted Berkowitz and his colleagues to investigate this link between childhood obesity and mothers’ weight problems.

His study involved 70 children whose growth was followed from birth to age 6; 33 children had overweight mothers (the high-risk kids), and 27 kids had lean mothers (the low-risk kids).

At regular doctor visits, the kids’ lean and fat body mass were measured.

At age 2, the kids’ weight and BMI were similar. By age 4, the high-risk kids were showing greater differences — with higher weight, BMI, and waist measurements. By age 6, high-risk kids began to show evidence of more fat.

“For the first time [at age 6] fat mass in the high-risk children was significantly greater than that in the low-risk children, as was percentage of body fat,” Berkowitz writes.

At age 6, 30 percent of the high-risk and 3 percent of the low-risk kids had high BMI. Six of the high-risk children were in highest BMI levels for their age. None of the low-risk kids were.

Some kids of overweight moms remained lean, he notes. “Their genes may be a little different, or their home environment may be different,” says Berkowitz.

“We know that once a kid is overweight — and if the family has weight problems — that’s a significant risk factor for later weight problems,” he tells WebMD.

Bottom Line: How to Fight Childhood Obesity?

There’s not an easy answer. “There are intervention programs for adolescents and teens, but not for kids this young,” Berkowitz says. Therefore, he advises: less fat in the diet, less sugar, fewer calorie-dense foods, less fried food, less junk food. “Also, it’s important to deal with inactivity. We need to promote healthy physical activity and cut down on TV watching.”

Moms need to face their own weight problems — then help their young children. “We don’t want moms to feel bad. But we need to help these children. A lot of this is either a combination of genetic predisposition and Western lifestyle, not a personal failing. I think parents and kids can work together to create a healthy family lifestyle,” Berkowitz tells WebMD.

But family ties to childhood obesity still aren’t fully explained. “If an overweight mother was to lose weight before her pregnancy, would that be protective for her child?” asks Kramer. “It goes to the question, how does obesity develop? Are these genes that are passed on that will develop in the child? Or does exposure to an obese mother during pregnancy affect metabolism of fat cells and nutrient metabolism in the prenatal period?”

Certainly there are lean parents whose kids fall prey to childhood obesity, Kramer notes.

“Genetics is not the entire story. The classic thing you’ll hear is that the obesity epidemic has developed over past 20 or 30 years, so genetic predisposition has been around for a long time. It’s just being awakened in this toxic environment. Your genetics puts you on the cliff, but environment pushes you off.”

By Jeanie Lerche Davis, reviewed by Michael W. Smith, MD

SOURCES: Berkowitz, R. American Journal of Clinical Nutrition, January 2005; vol 81: pp 140-146. Robert I. Berkowitz, MD, executive director, Behavioral Health Center, Children’s Hospital of Philadelphia. Robert Kramer, MD, pediatric gastroenterologist and nutritionist; and medical director, BEACH (Better Eating and Activity for Children’s Health) Clinic, Miller School of Medicine, University of Miami.