Risk Factors and Causes of Obesity

Many factors can contribute to obesity and overweight, including lifestyle choices (e.g., lack of exercise, too little sleep), medical conditions (e.g., hypothyroidism) and genetics (i.e., heredity). When a person takes in more calories than he or she uses, overweight and obesity result. These excess calories are stored in the body as fat, and unless weight-control strategies are put into place, more and more weight is gained.

People tend to gain weight when they eat high-calorie foods and do not get enough exercise, but there are other contributing factors, including the following:

  • Lifestyle habits often affect calorie consumption and exercise. People may drive instead of walk. Neighborhoods can be unsuitable for significant outdoor activity. Workplaces might have vending machines that offer only high-calorie snacks rather than healthy alternatives. People may not have time to cook low-calorie meals at home.
  • Certain social factors also may be linked to obesity. Poverty, for example, may cause some people to buy high-calorie processed foods because they typically cost less than healthier foods. Opportunities for exercise may be limited if there are no recreation areas in the neighborhood, if the area is considered unsafe or not conducive to activities like walking or jogging, and/or if gym memberships are too expensive.
  • Many people gain weight when they quit smoking. Food often tastes better and nicotine no longer speeds up the calorie-burning process.
  • Alcohol adds calories to the diet, increases appetite, and may interfere with a person's ability to make good choices about healthy meals and portion sizes.
  • In October 2012, results of a large study indicated that too little sleep can affect the function of fat cells and increase the risk for weight gain and related conditions like type 2 diabetes.

A number of medical factors also contribute to obesity and overweight, including the following:

  • Age (As people age, the amount of calories needed also changes, often due to reduced activity levels and slowed metabolism.)
  • Cushing's syndrome (This hormonal condition can cause increased fat around the neck and upper body, with thinning arms and legs.)
  • Hypothyroidism (When too little thyroid hormone is produced, the result is a slower metabolism and less energy for exercise.)
  • Medications (Some drugs, such as steroids, certain antidepressants, and medications to control seizures and psychiatric problems can slow down the body's metabolism, increase appetite, and cause the body to retain more water.)
  • In women, polycystic ovary syndrome (May also result in irregular or missed periods, small ovarian cysts, and high levels of the male hormone androgen.)
  • Psychological/emotional issues (Stress and boredom may lead people to eat more and exercise less.)

Obesity and overweight can be genetic (i.e., run in families). Genes have some control over the quantity and location of stored body fat. Therefore, obese parents are more likely to have obese or overweight children. However, it is important to note related lifestyle habits. If parents prepare high-calorie meals and do not encourage children to exercise, then obesity is likely to develop within the family.

Publication Review By: Karen Larson, M.D.

Published: 15 Nov 2006

Last Modified: 28 Sep 2015