Obesity is an abnormal accumulation of body fat and associated with increased risk of illness, disability, and death. The World Health Organization terms obesity a worldwide epidemic, and the diseases which can occur due to obesity are becoming increasingly prevalent. Much concern has been generated about the increasing incidence of obesity among Americans. Some studies have actually estimated that 50% of all Americans are overweight.
Obesity traditionally has been defined as a weight at least 20% above the ideal weight; 20% to 40% over ideal weight is considered mildly obese; 40–100% over ideal weight is considered moderately obese; and 100% over ideal weight is considered severely, or morbidly, obese. More recent guidelines for obesity use a measurement called BMI (body mass index). To calculate individual’s BMI weight in kilograms (kg) is divided by the height squared measured in meters (m). To calculate BMI in imperial units, weight in pounds (lb) is divided by height squared in inches (in) and then multiplied by 703. The formula for calculating the BMI of children is the same as for adults, but the resulting number is interpreted differently.
All adults age 20 and older are evaluated on the BMI scale as follows:
BMI below 18.5: Underweight
BMI 18.5-24.9: Normal weight
BMI 25.0-29.9: Overweight
BMI 30 and above: Obese
Some researchers consider a BMI of 17 or below an indication of serious, health-threatening malnourishment (anorexia nervosa). At the other end of the scale, a BMI of 40 or greater indicates morbid obesity.
Excessive weight can result in many serious, potentially life-threatening health problems, including hypertension, Type II diabetes mellitus (non-insulin dependent diabetes), increased risk for coronary disease, increased unexplained heart attack, hyperlipidemia, infertility, and a higher prevalence of cancer of colon, prostate, endometrium, and breast. that carries a very high risk of developing obesity-related diseases such as stroke, heart attack, and type II diabetes.
The mechanism for excessive weight gain is clear—more calories are consumed than the body burns, and the excess calories are stored as fat (adipose) tissue. However, the exact cause is not as clear and likely arises from a complex combination of factors.
Genetic factors significantly influence how the body regulates the appetite and the rate at which it turns food into energy (metabolic rate). Eating habits and patterns of physical activity also play a significant role in the amount of weight a person gains. Studies have indicated that the amount of fat in a person’s diet may have a greater impact on weight than the number of calories it contains. Obesity can also be a syndrome of certain disorders and conditions, including endocrinological (Cushing’s syndrome) or neurological diseases (damage to the hypothalamus) or a side effect to pharmaceutical treatment (steroids). A sedentary lifestyle and psychological factors in some cases can contribute to weight gain.
At what stage of life a person becomes obese can affect an ability to lose weight. In childhood, excess calories are converted into new fat cells (hyper-plastic obesity), while in adulthood excess calories only serve to expand existing fat cells (hypertrophic obesity). Since dieting and exercise can only reduce the size of fat cells, not eliminate them, persons who were obese as children can have great difficulty losing weight, since they may have up to five times as many fat cells as someone who became overweight as an adult.
Treatment of obesity depends primarily on how overweight a person is and his or her overall health. However, to be successful, any treatment must affect life-long behavioral changes rather than short-term weight loss. Behavior-focused treatment should concentrate on what and how much a person eats, how a person responds to food, how a person spends the time. Making activity and exercise an integrated part of everyday life is a key to achieving and maintaining weight loss. For individuals who are severely obese, dietary changes and behavior modification may be accompanied by bariatric surgery but it is still performed only on patients for whom other strategies have failed and whose obesity seriously threatens their health.
The primary factor in achieving and maintaining weight loss is a life-long commitment to regular exercise and sensible eating habits. Because most people eat more than they think they do, keeping a detailed food diary is a useful way to assess eating habits. Eating three or more (5-6) balanced, moderate-portion meals a day—with the main meal at mid-day—is a more effective way to prevent obesity than fasting or crash diets. Regular exercise should be combined with regular and healthful meals to maintain the weight loss for a long time.