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Obesity is defined as weight that exceeds 15 percent of normal weight for height and body type. Morbid obesity exceeds 20 percent of optimum weight. Obesity is considered a disease state. Life expectancy may be decreased in overweight and obese individuals.(1) An obese person is at high risk for developing a number of complications, including heart disease, high blood pressure, stroke, varicose veins, psychological stress, osteoarthritis, hyperlipidemia, and diabetes.(2, 3) However, weight is not the only factor in the development of disease. Body composition, the measurement of body fat and lean muscle mass, is now recognized as an important determinant of health. Body fat has important functions, including providing readily accessible energy during short periods of fasting. Fat is a structural component of organs, the nervous system, and skeletal muscles.
The distribution of body weight is also important. Recent studies have demonstrated that excess abdominal fat increases the risk of some diseases. "Apple" shaped women with waist to hip ratios of 0.8 or more, or waist measurements of 30 inches or more, appear to have a greater risk of developing heart disease and diabetes than "pear" shaped women.(4) The type of fat most insidious to health is the deep visceral fat that cushions the abdominal organs. Increased visceral fat is associated with higher levels of LDL cholesterol and lower levels of HDL cholesterol. It is possible that excess fat metabolism stresses the liver, rendering it less effective in metabolizing cholesterol. Visceral fat is also associated with insulin resistance and increased risk of diabetes.(5)
Obesity is influenced by a number of conditions. Basal metabolic rate, or the amount of energy burned at a resting state, is the major determinant of body weight. The ability of the body to convert energy (in the form of calories) to heat determines the basal metabolic rate. The basic law of thermodynamics states that heat expended must equal energy consumed. An imbalance on either end will result in weight loss or weight gain. Exercise is another determining factor. As lean muscle mass increases, so does the basal metabolic rate. A safe and effective weight-loss program is one that considers the laws of thermodynamics: energy burned must exceed energy consumed, and caloric restriction should be accompanied by exercise to maintain lean muscle mass.
Obesity can be caused by some metabolic disorders of the endocrine or pituitary systems. The pituitary, the thyroid, and the adrenal glands are important regulators of metabolism. Disorders such as hypothyroidism, hypopituitarism, and Cushing's syndrome can alter metabolic function and contribute to obesity. Insulin resistance, impaired glucose tolerance, and hyperinsulinemia can increase fat deposition and decrease lean muscle mass, influencing basal metabolic rate.
Some theories suggest that the origin of obesity is genetic. In fact, two obese parents are at greater risk of having children with adult weight problems.(6) This may be due, in part, to learned habits and poor dietary choices in childhood.(6, 7) Many people with overweight parents successfully manage their weight with diet and exercise once they reach adulthood. Given the astonishing number of overweight Americans, the more likely causes of obesity are behavioral. Overeating and lack of exercise are the principle behavioral factors that lead to obesity. As technology and transportation dominate the 21st century, lifestyles have become increasingly sedentary.(8) Societal pressure to produce and succeed leaves less time to plan and prepare wholesome meals. Advertising promotes processed, high fat, high-sugar, junk foods.
The recent discovery of the adipose-derived hormone leptin has led to advances in understandi
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