What is obesity?

Obesity is a long-term (chronic), complex disease in which having too much body fat (adipose tissue) increases your risk for developing other health problems. Obesity generally is measured by body mass index (BMI). A BMI of 30 or more is considered obese in adults.

If your BMI is between 25 and 30, you are overweight. See the topic Healthy Weight for information on maintaining a healthy weight.

What causes obesity?

Obesity is a result of many factors. Although it was once thought that a lack of will power—eating too much—and a lack of physical activity caused obesity, it is now recognized that family influence, genetics (including your basal metabolic rate, or BMR), and cultural and psychological factors all contribute to becoming obese.

To fit the medical definition of obesity, your extra weight must come from having too much body fat. Not everyone with a BMI over 30 is obese. For example, athletes may have a BMI over 30, but because their weight is due to muscle, not fat, they are not considered obese.

The main factor in obesity is an energy imbalance. People gain weight when they take in more energy (measured in calories) from food than they use through their BMR and physical activity. The excess energy is stored as fat.

What health problems does obesity put me at risk for?

If you are obese, you are more likely to develop type 2 diabetes, high blood pressure, heart disease or stroke, high cholesterol, breathing problems, sleep apnea, cancer, gallstones, arthritis, blood vessel problems, skin infections and rashes, sex hormone problems (including a decreased ability to have children), gout, heartburn, gastroesophageal reflux disease (GERD), liver problems, colon or kidney cancer, and endometrial cancer. If you lose weight, your risk for these conditions is reduced.

Often overlooked are the psychological and cultural problems associated with being obese. Stereotypes of obese people—such as that they are lazy—and the emphasis our society places on thinness may result in low self-esteem, a poor body image, depression, and eating disorders. Stereotypes also may make it more difficult for an obese person to find a job or to progress in one.

Although a high BMI does indicate an overall greater risk of health problems, the distribution of body fat is also important. If fat accumulates mostly around the abdomen (central obesity, sometimes called apple-shaped), you are more likely to develop heart disease, stroke, high blood pressure, and/or type 2 diabetes than people who are lean or people with fat around the hips (peripheral obesity, gynecoid or gluteofemoral obesity, or pear-shaped). The apple shape is more common in men, while the pear shape is more common in women.

How will my doctor diagnose obesity?

Your doctor will take your medical and family history and do a physical examination. He or she will use your BMI to determine whether you are obese. Your doctor may measure your waist or determine your waist-to-hip ratio (WHR) to determine how excess fat is distributed on your body. This helps determine your risk for other health problems.

If your weight or family history suggests you have an increased risk for developing health problems, your doctor may want to do more tests to check for those problems. The most common tests are blood tests to check for type 2 diabetes, thyroid problems, and excess cholesterol or triglycerides (fats) in your blood.

How is obesity treated?

Because obesity is a chronic disease, it requires long-term management. The focus is often on reducing the risk for developing health problems as much as on losing weight.

The U.S. National Heart, Lung, and Blood Institute (NHLBI) recommends that treatment be based on the degree of obesity and overall health risk status. If you are obese, you should try to initially lose about 10% of your current weight, at a rate of 1 lb (0.45 kg) to 2 lb (0.91 kg) per week using diet, physical activity, and self-monitoring. Approved weight-loss medication may be used, and in extreme cases surgery is used to reduce the size of the stomach.

Treatment also covers the psychological and social components of obesity. Stress management and counseling may be helpful. Getting family support and creating community contacts help you deal with the stereotypes and other social issues that are associated with obesity.

What does being obese mean to my lifestyle?

How obesity affects you depends on a number of factors, including your age, gender, fat distribution, and how physically active you are. For example, if you are an obese younger woman who gets regular physical activity, you may be at less risk for other health problems than an older man who is not physically active.

Being obese may make it more difficult to get out and socialize with others. The stereotypes of obese people may contribute to low self-esteem and emotional problems. However, you should make every effort to lead an active life. If you are surrounded by caring people, you may not be affected by the emotional and social negatives toward obesity.