More than half of the U.S. population is overweight. But being obese is different from being overweight. An individual is considered obese when weight is 20% (25% in women) or more over the maximum desirable for their height. When an adult is more than 100 pounds overweight, it is considered morbid obesity.

Obesity is also defined as a BMI (body mass index) over 30 kg/m2. Patients with a BMI between 25 and 29.9 are considered overweight, but not obese. See also diet and calories.

Rates of obesity are climbing. An ominous statistic is that the percentage of children and adolescents who are obese has doubled in the last 20 years.

The basic nutritional needs of most people are approximately 2,000 calories a day for women, and 2,500 for men. However, a professional athlete or manual laborer may need 4,000 or more. Pregnant women and nursing mothers require about 300-500 more calories/day than women who are neither pregnant nor nursing.

The body cannot store protein or carbohydrates, so excess protein or carbohydrate intake is converted to fat and stored. One pound of fat represents about 3,500 excess calories.

Obesity increases a person's risk of illness and death due to diabetes, stroke, coronary artery disease, hypertension, high cholesterol, and kidney and gallbladder disorders. Obesity may increase the risk for some types of cancer. It is also a risk factor for the development of osteoarthritis and sleep apnea.

Genetic factors play some part in the development of obesity -- children of obese parents are 10 times more likely to be obese than children with parents of normal weight.

• Consumption of more food than the body can use
• Excess alcohol intake
• Sedentary lifestyle