What Causes Obesity

Although there are genetic and hormonal influences on body weight, obesity occurs when you take in more calories than you burn through exercise and normal daily activities. Your body stores these excess calories as fat. Obesity usually results from a combination of causes and contributing factors, including: 

  • Inactivity. If you're not very active, you don't burn as many calories. With a sedentary lifestyle, you can easily take in more calories every day than you use through exercise and normal daily activities. 
  • Unhealthy diet and eating habits. Having a diet that's high in calories, eating fast food, skipping breakfast, eating most of your calories at night, drinking high-calorie beverages and eating oversized portions all contribute to weight gain. 
  • 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. 
  • Lack of sleep. Getting less than seven hours of sleep a night can cause changes in hormones that increase your appetite. You may also crave foods high in calories and carbohydrates, which can contribute to weight gain. 
  • Certain medications. Some medications can lead to weight gain if you don't compensate through diet or activity. These medications include some antidepressants, anti-seizure medications, diabetes medications, antipsychotic medications, steroids and beta blockers. 
  • Medical problems. Obesity can sometimes be traced to a medical cause, such as Prader-Willi syndrome, Cushing's syndrome, polycystic ovary syndrome, and other diseases and conditions. Some medical problems, such as arthritis, can lead to decreased activity, which may result in weight gain. A low metabolism is unlikely to cause obesity, as is having low thyroid function. 

Learn more about what causes obesity from the National Health Institute's Weight Control Network.