Childhood obesity is defined as a BMI above the 97th percentile for children of the same age and sex. Children with a BMI above the 90th percentile, but below the 97th percentile are considered to be overweight.

The number of overweight children in the U.S. has been rapidly increasing over the past few decades. Researchers say between 1971 and 1974, about 5 percent of American children (ages two to 19) were obese. By 2002, almost 15 percent of children were obese.

Even during childhood, excess weight can take a toll on the body. Overweight children are at high risk for developing high blood pressure, high cholesterol and respiratory problems. Type 2 diabetes, a condition that was typically seen in overweight, sedentary middle aged adults, is more commonly being diagnosed in children. In fact, the National Heart, Lung and Blood Institute estimates up to 45 percent of new cases of type 2 diabetes are being diagnosed in children. Overweight children are also at higher risk for poor self-esteem and teasing by peers.

Overweight and obesity are caused by taking in more calories than the body uses or burns. Several factors have contributed to the growing problems of excess weight in children. Fast food and take-out meals are a major source of nutrition for many children. Many of these foods are high in calories and fat. Snacks also tend to be high-calorie, high-fat products. Many children take a bus or are driven to school and activities. Children are also more likely to watch television, play video games or spend time on the computer than spend time in active outdoor play. In fact, the Surgeon General estimates 43 percent of adolescents watch more than two hours of television a day.

The health risks of being overweight in childhood are carried into adulthood. Researchers estimate 52 percent of obese three- to six-year-olds are still obese at 25. Overweight adults are at high risk for many types of chronic health problems, such as cardiovascular disease, respiratory ailments, sleep apnea, back pain, osteoarthritis, gallbladder disease and certain types of cancer.

Measuring Activity

The rate at which a person burns off calories is known as the metabolic rate. Researchers have studied metabolic rates in adults for some time and have a general idea of how many calories are burned during a particular activity. Children, however, have different rates of metabolism. So they may burn calories differently for various activities.

Researchers at Vanderbilt are using a metabolic chamber to study calorie intake and expenditure of children at rest and during various activities. Study children are placed in a special room for 24 hours. The doors and windows have special seals so doctors can monitor the ratio of oxygen and carbon dioxide in the room. Food is provided through a special window. There is also a toilet and sink for bathroom needs.

Mac Buchowski, Ph.D., Director of the Energy Balance Laboratory, explains each child goes through the same protocol. The day starts with sitting while eating breakfast followed by a short rest period. Throughout the day, a subject performs some type of activity, from playing a video game or typing on a computer to walking on a treadmill or riding on a stationary bike. Through minute by minute recordings of levels of oxygen and carbon dioxide, investigators can calculate how many calories are being used during a particular activity or rest period.

Sari Acra, M.D., M.P.H., a Pediatric Gastroenterologist at Vanderbilt University Medical Center, wants to use the information gained from the study to program portable activity monitors. Doctors will then have more accurate measurements to make recommendations for children needing to lose weight or maintain a healthy level of activity. Acra expects it will take two more years to complete the study. The information will then need to be analyzed to input data for the child-specific calorie monitors.

For general information on overweight and obesity in children:

American Heart Association

NAASO, The Obesity Society

National Heart, Lung and Blood Institute

Weight-control Information Network