Causes

Obesity is a chronic disease caused by a complex set of factors.

Genes

Obesity runs in families. If one or both of your parents are obese, your obesity risk is higher because genes determine your body shape and, to some extent, your weight. However, this isn't inevitable. Diet and exercise can help reduce this risk.

Fatty foods

Hot dogs, Big Macs®, french fries, macaroni and cheese, nachos, potato chips, ice cream -- all these high-fat American favorites are cheap, accessible and delicious. And all can lead to weight gain.

Lifestyle

If you spend most of your time at a desk or on a sofa, your risk for obesity increases. Likewise, the risk is higher for those whose fat intake makes up more than 30 percent of their daily caloric intake. People who get 20 to 30 minutes of exercise most days along with a low-calorie diet are less likely to be obese.

Metabolism

This is the rate your body uses food for energy. If your metabolism is slow, you are more likely to store extra calories as fat and need to work harder at losing weight. However, exercise may rev up your metabolism. Muscle burns more calories than fat, even at rest.

Fad diets

Constant dieting can lead to weight gain, particularly if you skip meals and starve yourself. You can seriously affect your body's metabolism, and when you go off the diet you are more likely to gain it all back and then some.

Psychology

Some people overeat, or binge, when they are stressed or depressed. Such eating temporarily relieves the stress of negative feelings. However, bingeing is usually followed by feelings of guilt, shame, disgust and depression.

Other causes

Some diseases and drugs can lead to obesity or weight gain. These include hypothyroidism, Cushing's syndrome and some neurological problems that can lead to overeating. Drugs such as steroids and some antidepressants may cause weight gain. See your doctor to find out if an underlying disease is contributing to your obesity.

More on Obesity

This article was reviewed and updated June 2007.