Obesity occurs when you eat and drink more calories than you burn through exercise and normal daily activities. Your body stores these extra calories as fat. Obesity usually results from a combination of causes and contributing factors, including:

  • Genetics. Your genes may affect the amount of body fat you store and where that fat is distributed. Genetics may also play a role in how efficiently your body converts food into energy and how your body burns calories during exercise. Even when someone has a genetic predisposition, environmental factors ultimately make you gain more weight.
  • 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 burn off through exercise and normal daily activities.
  • Unhealthy diet and eating habits. Having a diet that's high in calories, eating fast food, skipping breakfast, consuming high-calorie drinks and eating oversized portions all contribute to weight gain.
  • Family lifestyle. Obesity tends to run in families. That's not just because of genetics. Family members tend to have similar eating, lifestyle and activity habits. If one or both of your parents are obese, your risk of being obese is increased.
  • Quitting smoking. Quitting smoking is often associated with weight gain. And for some, it can lead to a weight gain of as much as several pounds a week for several months, which can result in obesity. In the long run, however, quitting smoking is still a greater benefit to your health than continuing to smoke.
  • 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. Not getting enough sleep at 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.
  • Age. Obesity can occur at any age, even in young children. But as you age, hormonal changes and a less active lifestyle increase your risk of obesity. In addition, the amount of muscle in your body tends to decrease with age. This lower muscle mass leads to a decrease in metabolism. These changes also reduce calorie needs and can make it harder to keep off excess weight. If you don't control what you eat as you age, you'll likely gain weight.
  • Social and economic issues. Certain social and economic issues may be linked to obesity. You may not have safe areas to exercise, you may not have been taught healthy ways of cooking, or you may not have money to buy healthier foods. In addition, the people you spend time with may influence your weight — you're more likely to become obese if you have obese friends or relatives.
  • Medical problems. Obesity can rarely 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.

Even if you have one or more of these risk factors, it doesn't mean that you're destined to become obese. You can counteract most risk factors through diet, physical activity and exercise, and behavior changes.

Jun. 07, 2013