Obesity is an excess proportion of total body fat. A person is considered obese when his or her weight is 20% or more above normal weight. The most common measure of obesity is the body mass index or BMI. A person is considered overweight if his or her BMI is between 25 and 29.9; a person is considered obese if his or her BMI is over 30. "Morbid obesity" means that a person is either 50%-100% over normal weight, more than 100 pounds over normal weight, has a BMI of 40 or higher, or is sufficiently overweight to severely interfere with health or normal function. Obesity occurs when a person consumes more calories than he or she burns. For many people this boils down to eating too much and exercising too little. But there are other factors that also play a role in obesity. These may include: Age: As you get older, your body's ability to metabolize food slows down and you do not require as many calories to maintain your weight. This is why people note that they eat the same and do the same activities as they did when they were 20 years old, but at age 40, gain weight. Gender: Women tend to be more overweight than men. Men have a higher resting metabolic rate (meaning they burn more energy at rest) than women, so men require more calories to maintain their body weight. Physical activity: Active individuals require more calories than less active ones to maintain their weight. Additionally, physical activity tends to decrease appetite in obese individuals while increasing the body's ability to preferentially metabolize fat as an energy source. Much of the increase in obesity in the last 20 years is thought to have resulted from the decreased level of daily physical activity. Psychological factors: Psychological factors also influence eating habits and obesity. Many people eat in response to negative emotions such as boredom, sadness, or anger. People who have difficulty with weight management may be facing more emotional and psychological issues; about 30% of people 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. Illness: Although not as common as many believe, there are some illnesses that can cause obesity. These include hormone problems such as hypothyroidism (poorly acting thyroid slows metabolism), depression, and some rare diseases of the brain that can lead to overeating. Obesity in the United States has been increasingly named as a major health issue in recent decades. While many developed countries have experienced similar increases, obesity rates in the United States are among the highest in the world. Of all countries, the United States has the highest rate of obesity. In 2008, the obesity rate among adult Americans was estimated at 32.2% for men and 35.5% for women. Obesity is the number 2 cause of preventable death in the United States. 60 million Americans, 20 years and older are obese, 9 million children and teens ages 6-19 are overweight. The number of overweight and obese individuals is so alarming because carrying extra pounds increases the risks of developing many diseases including: diabetes, cardiovascular disease, heart disease, stroke, and certain types of cancer, high blood pressure, high cholesterol, metabolic syndrome, sleep apnea, asthma, arthritis, gallbladder disease, liver disease, urinary incontinence, and depression. Obesity takes a toll on your wallet and your health: The annual cost of being obese is $4,879 for a woman and $2,646 for a man. Being overweight, meanwhile, costs $524 for women and $432 for men. Driving up the price-tag are employee sick days, lost productivity, short-term disability, emergency room care, and even the need for extra gasoline. Treating obesity and obesity-related conditions costs billions of dollars a year. By one estimate, the U.S. spent $190 billion on obesity-related health care expenses in