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Pathology => Human Diseases => Obesity
Obesity
INTRODUCTION
Obesity, medical condition characterized by storage of excess body fat. The human body naturally stores fat tissue under the skin and around organs and joints. Fat is critical for good health because it is a source of energy when the body lacks the energy necessary to sustain life processes, and it provides insulation and protection for internal organs. But the accumulation of too much fat in the body is associated with a variety of health problems. Studies show that individuals who are 20 percent or more overweight run a greater risk of developing diabetes mellitus, hypertension, coronary heart disease, stroke, arthritis, and some forms of cancer.
Most physicians use the body mass index (BMI) to determine desirable weights. BMI is calculated metrically as weight divided by height (kg/m2). People with a BMI of 25 to 29.9 are considered overweight and people with a BMI of 30 or above are considered obese.
Weight-height tables, such as those published by the Metropolitan Life Insurance Company, are also used as general measures of desirable weight ranges. These tables assign a range of weights for a particular height. For example, a man of 1.8 m (5 ft, 10 in) has a desirable weight range of 66 to 83 kg (146 to 184 lb), with an average of 75 kg (165 lb). A woman who is 1.6 m (5 ft, 4 in) has a desirable range between 53 and 70 kg (117 and 155lb), with an average of 62 kg (136 lb).
The BMI and weight-height tables only provide rough estimates of desirable weights and scientists recognize that many other factors besides height affect weight. Weight alone may not be an indicator of fat, as in the case of a bodybuilder who may have a high BMI because of a high percentage of muscle tissue, which weighs more than fat. Likewise, a person with a sedentary lifestyle may be within a desirable weight range but have excess fat tissue.
According to the National Institutes of Health, in the United States 97 million adults are overweight or obese-55 percent of the population. About 22.5 percent of the population is obese, up from 13 percent in 1960.
COMPLICATIONS
Obesity increases the risk of developing disease. According to some estimates compiled by the National Institute of Diabetes and Digestive and Kidney Diseases, almost 70 percent of heart disease cases in the United States are linked to excess body fat, and obese people are more than twice as likely to develop high blood pressure. Obese women are at nearly twice the risk for developing breast cancer, and all obese people have an estimated 42 percent higher chance of developing colon cancer. Almost 80 percent of patients with Type II, or noninsulin-dependent diabetes mellitus are obese. The risk of medical complications, particularly heart disease, increases when body fat is distributed around the waist, especially in the abdomen. This type of upper body fat distribution is more common in men than in women.
The social and psychological problems experienced by obese people are also formidable. Erroneous stereotypes about "fat" people are often translated into discriminatory practices in education, employment, and social relationships. The consequences of being obese in a world preoccupied with being thin are especially severe for women, whose appearances are often judged against an ideal of exaggerated slenderness.
CAUSES OF OBESITY
A calorie is the unit used to measure the energy value of food and the energy used by the body to maintain normal functions. When the calories from food intake equal the calories of energy the body uses, weight remains constant. But when more calories are eaten than the body needs, the body stores those additional calories as fat, causing subsequent weight gain. Consuming about 3,500 calories more than what the body needs results in a weight gain of 0.45 kg (1lb) of fat.
Research has revealed the important role of biological factors in the regulation of body weight. For instance, basal metabolic rate, the minimum energy required to maintain normal body function, affects body weight and weight loss because some individuals naturally use more calories to sustain basic body processes. The size and number of an individual's fat cells also help determine the amount of weight loss that is possible.
Obesity is partially determined by a person's genetic makeup. One groundbreaking study published in 1986 followed children who were adopted shortly after birth. The adoptees grew up to achieve adult weights that were more similar to their biological parents than their adoptive parents, indicating the influence of a person's genetic makeup in determining body weight.
Scientists are unclear about which genes affect human obesity. Studies of mice have isolated five genes that, when present in mutated form, play a role in obesity. So far, however, mutations of these genes have not been identified in obese people. Researchers believe the cause of obesity in humans is more complicated than in mice and involves the interactions of multiple genes with environmental factors such as diet and physical activity.
Changing lifestyles play a key role in the increasing prevalence of obesity. Surveys indicate that people eat at restaurants more frequently than in the 1970s, and foods are served in larger proportions than those served at home. Less time is devoted to exercise for both adults and children in lieu of longer work hours at sedentary jobs, a decline in physical education programs in schools, and increased participation in sedentary recreational activities such as browsing the internet, video games, movies, and television. In addition, many of the laborsaving devices of the modern lifestyle, such as personal computers, telephone extensions, and remote controls, promote a sedentary lifestyle.
TREATMENTS FOR OBESITY
° Diets
The most common and conservative treatment for obesity utilizes a nutritionally balanced, low calorie diet. Most health care professionals and commercial weight-loss programs recommend diets consisting of 1,200 to 1,500 calories per day, usually in the following proportions: 60 percent carbohydrate, 30 percent fat, and 10 percent protein. Research from university obesity treatment centers indicates that patients who follow a low calorie diet lose 10 percent of their initial weight in 20 weeks. Without further treatment, however, patients usually regain one-third of the weight in the following year.
A more aggressive approach for persons who are 40 or more pounds overweight includes very low calorie diets ranging from 400 to 800 calories per day. These diets are usually based on four to five servings of a liquid formula each day, and candidates must be carefully screened and medically supervised while on the diet. People on very low calorie diets lose approximately 15 to 20 percent of their initial body weight in 16 weeks and regain approximately one-half of that weight within a year.
° Exercise
Caloric restriction alone will not produce long-term weight loss. While the data from studies on the effect of exercise for short-term weight loss are contradictory, research clearly indicates that regular exercise is the single best predictor for achieving long-term weight control. Regular exercise will also improve some of the medical conditions associated with obesity including elevated blood cholesterol, high blood pressure, and diabetes.
° Behavior Modification
Many eating and exercise habits combine to promote weight gain. Certain times, places, activities, and emotions may be linked to periods of overeating or inactivity. Many obesity treatment programs recommend individuals keep a food diary that records all food or drink consumed, when and with whom it was consumed, and the mood or precipitating events that trigger eating. After one to two weeks, the diary may reveal a pattern of activities or negative emotions that lead to overeating. Once these eating cues are identified, techniques can be developed and practiced to prevent unwanted eating habits.
° Weight-Loss Medications
Weight-loss medications of any type are only appropriate for people with a BMI of 30 or above, or a BMI of 27 or above accompanied by weight-related medical conditions such as diabetes or high blood pressure. Amphetamine drugs used to be prescribed to combat obesity, but their well-documented side effects, including insomnia, anxiety, and tolerance (the need to take higher and higher doses to continue to produce the same effect), made them less popular by the late 1970s. A renewed scientific and commercial interest in weight-loss medications was prompted by the Food and Drug Administration's (FDA) approval of the appetite suppressant dexfenfluramine (sold under the brand name Redux) in 1996, the first weight-loss medication approved in the United States in over 20 years and the first ever approved for maintaining weight loss. Although never approved for long-term use by the FDA, a combination of two other drugs, phentermine and fenfluramine, popularly known as fen-phen, was used by millions of Americans to promote weight loss. Fenfluramine and dexfenfluramine were eventually associated with valvular heart disease, and the manufacturer withdrew these medications from the marketplace in 1997.
A new medication, sibutramine (sold under the brand name Meridia), was approved by the FDA for weight loss and the maintenance of weight loss in 1997. Unlike dexfenfluramine and fenfluramine, sibutramine does not appear to be associated with valvular heart disease, although a small number of patients may develop significant increases in blood pressure. This medication seems to increase fullness, making the required dietary changes for weight loss and the maintenance of weight loss easier to accomplish. In 1999 the FDA approved orlistat, a weight loss medication that works by blocking the absorption of fat. Scientists are also investigating the hormone leptin, which plays a role in obesity in mice, as a possible treatment for obesity in humans.
Over a six-month period, weight-loss medications may result in an approximately 10-percent body weight reduction. Weight loss slows or stops after six months, but discontinuing medication usually causes weight regain. The continued use of medications keeps most of the lost weight from returning for two years. Many experts recommend that medications for weight control be used chronically, like medications for diabetes and high blood pressure. Unfortunately, few studies have examined the consequences of long-term use of weight-control medications.
° Surgery
Surgery may be a viable option for patients who are extremely obese (with a BMI greater than 40) and suffer from serious medical complications due to weight. Among all obese persons in the United States, less than 2 percent meet weight criteria for surgery.
There are two accepted surgical procedures for reducing body weight: gastroplasty and gastric bypass. Although these two procedures use different methods, they both reduce the stomach to a pouch that is smaller than a chicken's egg, drastically limiting the amount of food that can be consumed at one time. Surgery produces 25 to 35 percent reductions in weight over the first year and most of this weight loss is maintained five years after surgery. More importantly, the serious medical conditions that accompany extreme obesity improve significantly. Surgery is not without risk and should be performed by skilled surgeons who provide patients with a comprehensive program for long-term weight control.
NEW DIRECTIONS IN WEIGHT CONTROL
The weight-loss goal of most dieters is typically to achieve an ideal weight as defined by a weight-height chart. More recently, however, the recommended goals for obesity treatment have become more modest: reduce body weight by about 10 percent. Research over the last decade indicates that 5- to 10-percent reductions in body weight are sufficient to improve medical conditions associated with obesity such as high blood pressure, diabetes, and elevated cholesterol levels. These significant health improvements occur even though patients may still be overweight.
These new weight-loss goals may be difficult for obese people to accept. Obese people often seek weights that may be biologically impossible to achieve or, if achieved, cannot be maintained. One study of overweight women found that the average weight goal was a 30 percent reduction in body weight. Clearly, seeking ideal weights is unrealistic-virtually no obesity treatment produces long-term, maintainable weight losses significant enough for patients to reach their ideal weights. Physicians and commercial weight-loss programs need to help obese people feel successful when more modest reductions in weight and significant improvements in health are achieved.
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