Obesity is an excessive accumulation of body fat that results from the storage of excess food energy (calories) in the body's fat cells. It affects approximately 30% of American adults.
Obesity results from an imbalance of the body's food intake, physical activity, and resting metabolism, causing a surplus of calories to be stored in fat cells. While various physiological and psychological factors play roles in obesity, genetic influences are significant, responsible for up to 30-50% of the total cause of obesity in certain families. Research has isolated a gene thought to control one of the major hormonal signals for fullness, indicating how heredity may affect obesity. Certain endocrine disorders, such as hypothyroidism or tumors of the adrenal gland, pancreas, or pituitary gland, may cause obesity. A reduction of the body's resting metabolic rate also has a significant effect on the development of obesity. Often obesity results from using food as an inappropriate coping mechanism to deal with emotional stress.
Obesity means an abundance of fat tissue, not merely an excess in body weight, which can result from an increase in muscle mass or body fluid. The degree of obesity may be expressed in terms of the Body Mass Index (BMI), calculated as weight in kilograms divided by height in meters squared, wt/ht6. Obesity is defined as a BMI above 30. Individuals who weigh more than 20% above their "ideal body weight" according to the standard height and weight tables of the Metropolitan Life Insurance Company may be judged as obese. This is only a rough guide for obesity. More accurate and reliable methods of assessing obesity include measuring the skin fold thicknesses of three different parts of the body, weighing an individual under water, measuring total body water, or using the body distribution of fat-soluble gases.
Obesity may be classified according to the age of onset, family history, degree of obesity, and fat cell size and distribution. Juvenile-onset obesity is characterized by increased numbers of fat cells with a more severe degree of obesity and is usually more resistant to treatment. Obesity in adults is characterized by increased fat cell size and is more prone to cause heart disease, diabetes, and other medical complications; however, it is more easily treated, with better long-term results.
Obesity significantly increases the risk of premature death, heart attack, diabetes mellitus, hypertension, atherosclerosis, gallbladder disease, osteoarthritis, and certain cancers. Research has shown that individuals with an apple shapeÑfat in the upper body or abdomenÑhave a greater risk for medical diseases than those with a pear shapeÑfat in the lower body or hips. There is some indication of a higher rate of psychological dysfunction in the obese population, and there also exists a strong negative bias against the obese person in social, economic, and quality of life situations.
The treatment of obesity is complex, frustrating, and disappointing, as most of those who lose weight often regain it. For best results treatment should stress: (1) a reduction of fat intake to below 20% of the total daily caloric intake (see dieting); (2) a reduction of daily caloric intake to below what is expended from physical activity and the body's resting metabolic rate; (3) regular physical exercise; and (4) a realistic psychological and emotional orientation that establishes new eating behaviors.Appetite suppressant drugs that work on specific brain neurotransmitters to suppress food intake and control eating have been developed and are now being used under medical supervision. In very difficult cases, stomach stapling surgery may be an effective option for severely obese people with serious health problems. Diet "aids," such as thyroid medication, body wraps, fad diets, food combining, laxatives, or water pills, do not help and are often harmful. The successful treatment of ity requires lifelong changes in eating behavior.