Obesity occurs when a person consumes more calories than they need for the energy they use. Several different factors may influence weight gain.
About 90% of people who lose weight through dieting gain every pound back regardless of their weight-loss method.
Genetic factors may play some part in 70 - 80% of obesity cases.
The Biological Pathway to Appetite
Appetite is determined by processes that occur both in the brain and gastrointestinal tract. Eating patterns are controlled by areas in the hypothalamus and pituitary glands (in the brain).
The body produces a number of molecules that increases or decreases appetite, including leptin. Leptin is a hormone that fat cells release. Some scientists think this hormone may also be released by cells in the stomach. Leptin appears to play an important role in insulin resistance and fat storage in the body, but its role in obesity is unclear.
The most likely scenario is that leptin levels rise as the cells store more fat. This increase in leptin levels decreases appetite. Falling levels of leptin make you feel hungry. In people who have genetically lower levels of leptin, however, the brain may be tricked into thinking that it is always starving because there is no leptin to decrease appetite. This can lead to weight gain.
Specific Genetic Factors
Genetics may directly contribute to severe obesity in people with family histories of the problem. Genetic factors such as slow metabolisms may also make people more likely to be overweight, and there have been some genetic mutations identified in rare causes of severe obesity.
Review Date: 04/14/2010
Reviewed By: A.D.A.M. Editorial Team: David Zieve, MD, MHA, and David R. Eltz. Previously reviewed by Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital (4/14/2010).