The causes of obesity are complex, and can include genetic, biological, behavioral, nutritional and cultural factors. The root causes are excess consumption of food, a lack of physical activity or both. Obesity occurs when a person eats more calories than his or her body burns up.
A child with one obese parent has a 50 percent chance of being obese. When both parents are obese, their children have an 80 percent chance of obesity.
Many genetic and environmental factors contribute to the number of calories people eat and burn up, which is why weight loss and gain varies for different people.
Obesity increases the risk of many serious health problems, and is linked to more than 30 medical conditions. Scientific evidence has established a strong relationship with at least 15 of those conditions, some of which include:
Reviewed by health care specialists at UCSF Benioff Children's Hospital.
Last updated July 14, 2010
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