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"Obesity" specifically refers to an excessive amount of body fat. "Overweight" refers to an excessive amount of body weight that includes muscle, bone, fat, and water. Today, about 65 percent of adults in the United States are overweight or obese. Obesity puts people at increased risk for chronic diseases such as heart disease, type 2 diabetes, high blood pressure, stroke, and some forms of cancer.

Body Mass Index


The body mass index (BMI) is a tool used to assess overweight and obesity and monitor changes in body weight. It has limitations because it does not measure body fat or muscle directly. BMI is calculated by dividing a person's weight in pounds by height in inches squared and multiplied by 703.

Two people can have the same BMI but different body fat percentages. A bodybuilder with a large muscle mass and low percentage of body fat may have the same BMI as a person who has more body fat. However, a BMI of 30 or higher usually indicates excess body fat.

The BMI table provides a useful guideline to check your BMI. First, find your weight on the bottom of the graph. Go straight up from that point until you come to the line that matches your height. A BMI of 25 to 29.9 indicates a person is overweight. A person with a BMI of 30 or higher is considered obese.


Obesity occurs when a person consumes more calories from food than he or she burns. Our bodies need calories to sustain life and be physically active, but to maintain weight we need to balance the energy we eat with the energy we use. When a person eats more calories than he or she burns, the energy balance is tipped toward weight gain and obesity. This imbalance between calories-in and calories-out may differ from one person to another. Genetic and environmental factors may all play a part. At the molecular level, a protein called leptin has been shown to play a central role in obesity.

In less than 1% of cases, obesity is caused by a disease, such as Cushing's syndrome, hypothyroidism, or polycystic ovarian disease.


Physical Activity

Physical activity helps you control your weight by using excess calories that would otherwise be stored as fat. Most foods you eat contain calories, and everything you do uses calories. Balancing the calories you eat with the calories you use through physical activity will help you reach and maintain a healthy weight.

Experts recommend at least 30 minutes of moderate-intensity physical activity on most, if not all, days of the week. Physical activity may include structured activities such as walking, running, basketball, or other sports. It may also include daily activities such as household chores, yard work, or walking the dog. Pick a combination of structured and daily activities that fit your schedule.


For slightly overweight people (BMI 25-30), follow a healthy eating plan which:

  • Emphasizes fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products.
  • Includes lean meats, poultry, fish, bean, eggs, and nuts.
  • Is low in saturated fats, trans fats, cholesterol, salt (sodium), and sugars.

For obese people with BMI greater than 30, a doctor may recommend very low-calorie diet (VLCD) that typically uses commercially prepared formulas to promote rapid weight loss. These formulas, usually liquid shakes or bars, replace all food intake for several weeks or months. VLCD formulas need to contain appropriate levels of vitamins and micronutrients to ensure that patients meet their nutritional requirements. Some physicians also prescribe very low-calorie diets made up almost entirely of lean protein foods, such as fish and chicken. People on a VLCD consume about 800 calories per day or less.


Appetite suppressants. Most available weight-loss medications approved by the Food and Drug Administration (FDA) are appetite-suppressant medications. These include sibutramine, phentermine, phendimetrazine, and diethylpropion. Appetite-suppressant medications promote weight loss by decreasing appetite or increasing the feeling of being full. These medications make you feel less hungry by increasing one or more brain chemicals that affect mood and appetite. Phentermine and sibutramine are the most commonly prescribed appetite-suppressants in the United States.

NOTE: Amphetamines are a type of appetite suppressant. However, amphetamines are not recommended for use in the treatment of obesity due to their strong potential for abuse and dependence.

Lipase inhibitors. The drug orlistat reduces the body’s ability to absorb dietary fat by about one-third. It does this by blocking the enzyme lipase, which is responsible for breaking down dietary fat. When fat is not broken down, the body cannot absorb it, so it is eliminated and fewer calories are taken in. In 2007, orlistat was approved for over-the-counter (OTC) sale for adults age 18 and over. This means that the drug may be purchased without a prescription.


Severe obesity is a chronic condition that is difficult to treat through diet and exercise alone. Bariatric surgery is an option for people who are severely obese and cannot lose weight by traditional means or who suffer from serious obesity-related health problems. The operation promotes weight loss and reduces the risk of type 2 diabetes by restricting food intake and, in some operations, interrupting the digestive process to prevent the absorption of some calories and nutrients. Recent studies suggest that bariatric surgery may even have a favorable impact on mortality (death) rates in severely obese patients. The best results are achieved when bariatric surgery is followed with healthy eating behaviors and regular physical activity.


Weight-control Information Network