What Causes Obesity?

What causes obesity? Many people believe the answer to this question is very simple: eating too many calories or burning too few calories. However, if eating and exercise were the only causes of obesity, the treatment would be easy: eat less and exercise more.

Yet so many people with obesity have tried this simple treatment and failed. Did they just not try hard enough?

The truth is, obesity is a complex disease that makes treatment challenging. The main causes of obesity often involve a combination of factors, such as: environment, genetics, medications, psychological factors, diseases, hormones and bacteria, and lifestyle choices. These factors often work together to cause obesity, and as a result, no single treatment is effective for everyone.

Environmental Causes of Obesity

Where you live is a factor associated with obesity. If you live in a community that offers several high-calorie, fast food restaurants, you are more likely to have obesity. The same is true if you live an area without a local grocery store that sells fresh fruits and vegetables, or if you live in a community without sidewalks or that is unsafe to walk.^(1,2)

Genetic Causes of Obesity

Genetic factors — those you inherit from one or both parents — can cause obesity. If one or both parents have obesity, you have an increased risk of developing the disease. There are 79 known gene-specific obesity syndromes.⁽³⁾

Genes can also be responsible for how foods taste, if a person is more likely to snack between meals, or if a person is more likely to continue eating even when they are not hungry.⁽⁴⁾

Diseases That Can Cause Obesity

Cushing’s disease, sleep apnea and polycystic ovarian syndrome are diseases that can cause obesity.⁽¹⁾ These diseases cause obesity by changing metabolism and increasing certain hormones, making weight loss more difficult.

Medications That Can Cause Obesity

Many medications have been known to cause to obesity.⁽⁵⁾ Such medications include those used to treat mental illness, high blood pressure or heart rate, rheumatoid arthritis, and diabetes.⁽⁵⁾ If you think a medication is causing weight gain, it is important to continue taking the medication until you have discussed your concern with your doctor or healthcare provider.

Other Causes of Obesity

Prolonged stress and insomnia are known causes of obesity. These conditions can increase cortisol and insulin, both of which are hormones that can lead to obesity.^(6,7)

GLP-1, ghrelin, and leptin are hormones found in the stomach, fat cells, and intestines that work to signal our brain when we are hungry or when we are full. When these hormones are not working properly, obesity can develop.

Certain bacteria have been found in the intestines of people with obesity, and are thought to be associated with causing the disease.⁽⁸⁾ It is still unclear how or why this association occurs.⁽⁸⁾

Obesity is a complicated disease and what causes obesity is more than just eating too many calories or exercising too little. Often many factors work together to cause obesity. As a result, finding a treatment that works can be challenging and often requires more than eating less and exercising more.