What is obesity?

Obesity is defined as an excess proportion of total body fat. Nearly 72 million adults in the United States can be defined as obese. There are several indexes used to assess obesity. The most common measure of obesity is the body mass index (BMI).

What causes obesity?

In scientific terms, obesity occurs when a person's calorie intake exceeds the amount of energy he or she burns. What causes this imbalance between consuming and burning calories is unclear. Evidence suggests that obesity often has more than one cause. Genetic, environmental, psychological, and other factors all may play a part.

Genetic: Obesity tends to run in families, suggesting that it may have a genetic cause. However, family members share not only genes but also diet and lifestyle habits that may contribute to obesity. Separating these lifestyle factors from genetic ones is often difficult. Still, growing evidence points to heredity as a strong determining factor of obesity. In one study of adults who were adopted as children, researchers found that their subjects' adult weights were closer to their biological parents' weights than their adoptive parents'. The environment provided by the adoptive family apparently had less influence on the development of obesity than the person's genetic makeup.

Nevertheless, people who feel that their genes have doomed them to a lifetime of obesity should take heart. As discussed in the next section, many people genetically predisposed to obesity do not become obese or are able to lose weight and keep it off.

Environmental factors: Although genes are an important factor in many cases of obesity, a person's environment also plays a significant part. Environment includes lifestyle behaviors, such as what a person eats and how active he or she is. Americans tend to have high-fat diets, often putting taste and convenience ahead of nutritional content when choosing meals.

While people can't change their genetic makeup, they can change what they eat and how active they are. Some people can lose weight and keep it off by:

  • Learning how to choose more nutritious meals that are lower in fat.
  • Learning to recognize environmental cues (such as enticing smells) that may make them want to eat when they are not hungry.
  • Becoming more physically active.
  • Cutting down on portion sizes.

Psychological factors: Psychological factors also may influence eating habits. Many people eat in response to negative emotions such as boredom, sadness, or anger.

While most overweight people have no more psychological disturbances than people at their normal weight, about 30 percent of those who seek treatment for serious weight problems have difficulties with binge eating. During a binge eating episode, people eat large amounts of food while feeling they can't control how much they are eating. Those with the most severe binge eating problems are considered to have what is called binge eating disorder. These people may have more difficulty losing weight and keeping the weight off than people without binge eating problems. Some will need special help, such as counseling or medication, to control their binge eating before they can successfully manage their weight.

Other causes of obesity: Some illnesses can lower the metabolism or trigger an increased appetite which can cause obesity. These include hypothyroidism, Cushing's syndrome, depression, and certain neurologic problems. Certain drugs, such as steroids and some antidepressants, may cause excessive weight gain through the same methods. A doctor can determine if a patient has any of these conditions, which are believed to be responsible for only about one percent of all cases of obesity.

What are the health risks related to obesity?

Obesity is not just a cosmetic problem. It's a health hazard. Someone who is 40 percent overweight is twice as likely to die prematurely as an average-weight person. (This effect is seen after 10 to 30 years of being obese.)

Obesity has been linked to several serious medical conditions, including diabetes, heart disease, high blood pressure, and stroke. It is also associated with higher rates of certain types of cancer. Obese men are more likely than non-obese men to die from cancer of the colon, rectum, and prostate. Obese women are more likely than non-obese women to die from cancer of the gallbladder, breast, uterus, cervix, and ovaries.

Other diseases and health problems linked to obesity include:

  • Gallbladder disease and gallstones
  • Osteoarthritis, a disease in which the joints deteriorate, possibly as a result of excess weight on the joints
  • Gout, another disease affecting the joints
  • Pulmonary (breathing) problems, including asthma and sleep apnea, in which a person can stop breathing for a short time during sleep

Doctors generally agree that the more obese a person is, the more likely he or she is to have health problems. People who are 20 percent or more overweight can gain significant health benefits from weight loss. Many obesity experts believe that people who are less than 20 percent above their healthy weight should try to lose weight if they have any of the following risk factors.

  • Family history of certain chronic diseases: People with close relatives who have had heart disease or diabetes are more likely to develop these problems if they are obese.
  • Pre-existing medical conditions: High blood pressure, high cholesterol levels, or high blood sugar levels are all warning signs of some obesity-associated diseases.
  • "Apple" shape: People whose weight is concentrated around their abdomens may be at greater risk of developing heart disease, diabetes, or cancer than people of the same weight who are "pear-shaped."

Fortunately, even a modest weight loss of 10 to 20 pounds can bring significant health improvements, such as lower blood pressure and cholesterol levels.

When should I seek professional help?

It is best to be open and honest with your doctor about your attempts at weight loss because the more weight you gain, the more health risks increase. You should call your doctor if you need help in losing weight or if you fall into either of these categories:

  • Body mass index (BMI). If your BMI is 30 or greater, you're considered obese and should talk to your doctor about losing weight for your health.
  • Waist circumference. If you have an "apple shape" — a "potbelly" or "spare tire" — you carry more fat in and around your abdominal organs. Fat in your abdomen increases your risk of many of the serious conditions associated with obesity. Women's waist measurement should fall below 35 inches. Men's should be less than 40 inches. If you have a large waist circumference, talk to your doctor about weight loss.

How is obesity treated?

The treatment of obesity needs to be long-term; it cannot be short-term. Weight loss should be gradual and careful follow-up is necessary to prevent rebound weight gain. Changing behavior and lifestyle are the only ways to change a person's weight permanently. These changes focus on gradual, permanent changes in eating and exercise habits. There are six ways you can change your behavior and lifestyle that will help you maintain weight loss:

  • Learning about nutrition
  • Changing your eating habits
  • Increasing your physical activity
  • Changing your attitudes about eating
  • Joining a weight loss program
  • Developing support systems
  • Following any drug therapies ordered by your doctor.

The keys to weight management include making lifestyle changes, such as increasing exercise and activity and changing dietary habits. Drug therapy may also help the patient learn and adapt to a healthier lifestyle.

Prescription drugs are another approach to treating obesity. An ideal anti-obesity drug should help you lose weight, but it should also help you to maintain your weight loss. It should be used along with a program of diet and exercise and should help you follow your overall treatment plan. Preferably, at least 75 percent of the weight lost should be fat. The drug should be safe enough that its benefits outweigh the risk of any complications, and it should not have a potential for being abused.

The anti-obesity medications that are currently available, such as Meridia® (sibutramine), work mainly by suppressing the appetite. They raise specific hormones such as noradrenalin or serotonin in the nervous system, creating a feeling of fullness. These medications will not work, however, unless you also make changes in your diet and lifestyle.

The level of success with anti-obesity drugs is rather modest. Studies show a mean weight loss of six to 10 pounds total and about one-half pound a week greater weight loss than with a placebo (for 12 weeks or less of treatment). Some individuals respond very well while others may not respond at all.

Another treatment option may be surgery. Surgery should only be considered after all other attempts to lose weight have been unsuccessful, or if a person has an obesity-related disease. Surgery should only be done at centers committed to long-term follow-up and as an addition to diet, exercise, and behavior modification programs. Currently, candidates for these surgeries have to be:

  • Severely obese (A BMI greater than 35)
  • Well-informed
  • Assessed by dietician, psychologist, endocrinologist, and other specialists before being considered for the procedure

Surgical procedures have had the most long-term success, but it is important to consider the reasons for success or failure of previous weight-loss attempts as well as the risks and benefits of the surgery.


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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 1/28/2010…#9468