Obesity : Causes

Although there are genetic and hormonal influences on body weight, ultimately excess weight is a result of an imbalance of calories consumed versus calories burned through physical activity. If you consume more calories than you expend through exercise and daily activities, you gain weight. Your body stores calories that you don't need for energy as fat.

The following factors — usually working in combination — can contribute to weight gain and obesity.

* Diet. Regular consumption of high-calorie foods, such as fast foods, or increasing their portion sizes contributes to weight gain. High-fat foods are dense in calories. Loading up on soft drinks, candy and desserts also promotes weight gain. Foods and beverages like these are high in sugar and calories. In general, eating away from home also increases calorie intake.
* Inactivity. Sedentary people are more likely to gain weight because they don't burn calories through physical activities.
* Quitting smoking. Smokers tend to gain weight after quitting. This weight gain may be partially due to nicotine's ability to raise the rate at which your body burns calories (metabolic rate). When smokers stop, they burn fewer calories. Smoking also affects taste; quitting smoking makes food taste and smell better. Former smokers often gain weight because they eat more after they quit. However, cigarette smoking is still considered a greater threat to your health than is extra weight.
* Pregnancy. During pregnancy a woman's weight necessarily increases. Some women find this weight difficult to lose after the baby is born. This weight gain may contribute to the development of obesity in women.
* Certain medications. Corticosteroids and tricyclic antidepressants, in particular, can lead to weight gain. So can some high blood pressure and antipsychotic medications.
* Medical problems. Uncommonly, obesity can be traced to a medical cause, such as low thyroid function or excess production of hormones by the adrenal glands (Cushing's syndrome). A low metabolic rate is unlikely to cause obesity. In addition, it's unclear whether polycystic ovarian syndrome contributes to obesity. Some medical problems, such as arthritis, can lead to decreased activity, which may result in weight gain.