Having obese parents is the factor that most increases the likelihood of childhood obesity, according to Stanford University School of Medicine researchers.

By identifying the risk factors that lead to childhood obesity, the researchers hope to pave the way toward preventive measures.

The International Obesity Task Force recently suggested that as least 155 million school-age children worldwide are overweight or obese.

"The findings of the Stanford study suggest that at-risk children may be identifiable in the first few years of life," said W. Stewart Agras, MD, professor emeritus of psychiatry and behavioral sciences, whose team assessed both established and hypothesized risk factors. He went on to say "several of the identified risk factors are amenable to intervention, which could lead to the development of early prevention programs." The study appears in the July issue of Pediatrics.

During the exploratory study of 150 children, Agras and his colleagues began tracking 74 boys and 76 girls and their parents upon the child's birth. Attributes and behaviors were assessed until the child was 5 years old and were then used to predict whether the child would be overweight at 9.5 years. Monitored areas included parent weight, infant weight, parent/infant feeding practices, parent eating behaviors, child eating behaviors, child caloric intake, child activity, child temperament, child sleep time and parents' concerns about their child's weight, among others.

The researchers found that 25 percent of the children were in the 85th percentile of BMI at 9.5 years of age, including 9 percent that were in the 95th percentile. They also found that 64 percent of children with overweight parents became overweight, compared with 16 percent of those with normal-weight parents. Agras said parental obesity represented the most potent risk factor, a finding that confirms previous observations, and the connection between overweight parents and overweight children is likely due to a combination of genetics and family environmental influences.

Agras also noted that a child's temperament altered the effect of a parent's obesity; 46 percent of children with a sensitive disposition and an overweight parent became overweight, compared with 19 percent of children without this disposition. Temperament also played a role in weight for children with normal-weight parents. Agras said it is likely that parents with emotional children feed them to reduce the frequency of tantrums instead of using non-food methods. "It's probably not a good idea to use food as a calmer," he said, adding that parents of these children might benefit from education programs. "If we can identify kids with difficult temperaments we could educate parents not to use food as a reward."

Other significant risk factors identified in the study were low parental concerns about their child's thinness and less sleep for the children. On average, overweight children got 30 fewer minutes of sleep than normal-weight children. The finding on sleep replicates previous findings but is not well understood, Agras said. "We don't know at all how this works," he said, adding that more studies are needed. "One possibility is that the kids sleep less because they're less active during the day."

Agras noted that the study, which was funded by the National Institute of Child Health & Human Development, has several limitations. The sample size is relatively small, he said, while the level of patient education is higher and the number of minorities is lower than in the general population. Past studies have shown that black and Hispanic children have a higher risk of being overweight than do white children. In addition, some assessments were obtained from parents, so bias could exist.

How big should your child be?

Each time you take your child to an annual checkup, most likely the first thing the doctor or nurse does is record your child's current height and weight. The two numbers are then plotted on separate gender-specific graphs to indicate what percentile your child falls into. This result is sometimes a surprising measure of much your child has grown over the past year. But what do these percentiles really tell you?

Well, it's a good indication of whether your child is growing steadily or heading off the "curve." For example, a child who consistently has had a weight percentile of 50 percent, but is now at 75 percent, may be headed toward obesity.

While these percentile charts can give you an idea of how your child is growing, many doctors are now using another growth measure called a body mass indicator (BMI). The BMI calculator compares a child's weight and height for her age, coming up with one number, rather than separate ones. This calculation is particularly helpful for identifying children and adolescents who are at risk for becoming significantly overweight, because there's a strong correlation between BMI and body fat.

What's your child's BMI? You can find online calculators, but to do it by hand you can use this method: Take your child's height and multiply it by itself. Then divide his weight by the number you got from the height equation. Once you have that answer, multiply it by 703.