In the United States, more than 60 million adults are obese, meaning they are 20 per cent or more above the ideal weight for a person's height. Complications from obesity can include heart disease, diabetes and high blood pressure. Obesity results from environmental and lifestyle factors, which can be controllable, and from physiological factors, for which there is no conscious control. The physiological factors are genetically regulated.

A genetic link to obesity was strongly inferred by the results of studies involving twins who were raised apart. The study allowed the influences of genetic make-up and environment to be distinguished. These studies determined that genetic factors contribute to about 40 per cent of obesity variance in twins. Although genetic factors alone can not explain the large increase in the prevalence of childhood and adolescent obesity, interactions between genetics and environmental factors are likely. A person with a genetic...