But this simple statement belies the complex chemistry of the human body. Genetic, metabolic and environmental factors all play a role in energy regulation. And these differences explain why some people gain weight eating almost nothing while others eat constantly and never gain an ounce. While the cause of some obesity has been defined, as in the case of Prader-Willi Syndrome , or in small groups of people found to have a specific genetic mutation, such as leptin deficiency, most obesity is much more complex. Over the past 10 years scientists have uncovered many genes that contribute to feeding behavior and energy regulation, and current research indicates that defects in a number of brain and gut peptides play a role in weight.
Researchers believe that most obesity is caused by small differences in food intake.
As was found in the Framingham Heart Study , most adults will gain 20 pounds between 25 and 55 if no steps are taken to avoid weight gain. But that 20 pound gain represents a very small calorie excess, perhaps a tenth of a percent per year. Obesity and genetics. Twin and adoptee studies indicate that there is a strong genetic basis for obesity. Studies on large populations of adopted children show that there is no relationship between body weight and adoptive parents, but a close correlation with biological parents.