Obesity.

Obesity. I 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 overweight or obese run a greater risk of developing diabetes mellitus, hypertension, coronary heart disease, stroke, arthritis, and some forms of cancer. According to the Centers for Disease Control and Prevention (CDC), in the United States nearly 31 percent of the population is obese, up from 13 percent in 1960. From 1980 to 2000 obesity among American adults doubled, and the number of obese children and teenagers nearly tripled. Public health officials are concerned that obesity is reaching epidemic proportions. The health problems resulting from obesity could reverse many of the health gains achieved in the United States in recent decades. II MEASURING OBESITY The body mass index (BMI) is commonly used to determine desirable body weights. BMI is a measure of an adult's weight in relation to height, and it is calculated metrically as weight divided by height squared (kg/m2). People with a BMI of 25.0 to 29.9 are considered overweight and people with a BMI of 30 or above are considered obese . Body mass index only provides a rough estimate of desirable weight, however. Physicians 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. In general, however, the higher the BMI, the greater the risk for developing serious medical conditions. III COMPLICATIONS OF OBESITY Obesity increases the risk of developing disease. According to 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 hypertension. 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. Obese women are at nearly twice the risk for developing breast cancer, and all obese people have a 42 percent higher chance of developing colorectal cancer. Almost 80 percent of patients with Type 2 diabetes mellitus, also known as noninsulin-dependent diabetes mellitus, are obese. Obese people also experience social and psychological problems. Stereotypes about "fat" people often translate 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. IV 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 a person consumes more calories 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 (1 lb) of fat. A Biological Factors 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. B Genetics 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. More than 250 genes that may play a role in obesity have been identified in mice and humans. Researchers believe that the cause of obesity in humans is complicated and most likely involves the interactions of multiple genes with lifestyle factors such as diet and physical activity. C Lifestyle Changing lifestyles over the last century, including increased calorie consumption and reduced physical activity, have played a key role in the prevalence of obesity seen today. In the United States and other developed nations, the availability of wider food options has contributed to a change in eating habits. Grocery stores stock their shelves with a greater selection of products. Prepackaged foods, soft drinks, and fast-food restaurants have become more accessible. While such food choices offer convenience, they also tend to be high in fat, sugar, and calories. Portion size has also increased. People eat more during a meal or snack because of larger portion sizes. Surveys indicate that people eat at restaurants more frequently than in the 1970s, and restaurants typically serve larger portions of food than those served at home. In the United States, experts believe that high-calorie food choices and larger portions have become the basis of the typical diet, resulting in excessive calorie intake and increasing the prevalence of obesity. Both adults and children spend less time devoted to exercise as a result 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, playing video games, and watching television. In addition, many of the laborsaving devices of the modern lifestyle, such as cars, elevators, personal computers, and remote controls, promote a sedentary lifestyle. According to some studies, more than 26 percent of adults reported no leisure-time physical activity. This lack of physical activity has reduced the overall amount of energy expended in the course of a day, contributing to the development of obesity. V TREATMENTS FOR OBESITY Obesity can become a chronic lifelong condition caused by overeating, physical inactivity, and even genetic makeup. No matter what the cause, however, obesity can be prevented or managed with a combination of diet, exercise, behavior modification, and in severe cases, weight-loss medications and surgery. A 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 more than 20 kg (40 lb) 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. 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. Once they go off a very low calorie diet, they typically regain approximately one-half of that weight within a year. Meal replacements are liquid shakes or portion-controlled meals that are substituted for one or two meals a day. They are typically used as part of a 1,200 to 1,500 calorie diet. Studies have shown that meal replacements are often more effective than very low calories diets, resulting in an increase in the amount of initial weight loss and enabling dieters to maintain their weight loss. Unlike very low calorie diets, meal replacements do not require that candidates receive extensive medical monitoring. B 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, hypertension, and diabetes mellitus. C 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. D 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 mellitus or hypertension. Amphetamine drugs were formerly 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 approval by the Food and Drug Administration (FDA) of the appetite suppressant dexfenfluramine (sold under the brand name Redux) in 1996. Dexfenfluramine was 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 drugs, phentermine and fenfluramine, or phentermine and dexflenfluramine, 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. The FDA has approved two medications, sibutramine and orlistat, for long-term use in the treatment of obesity. Sibutramine (sold under the brand name Meridia) increases fullness, making the required dietary changes for weight loss and the maintenance of weight loss easier to accomplish. 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. Orlistat (sold under the brand name Xenical) 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 a 10-percent body weight reduction. Weight loss slows or stops after six months, and 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 continuously, like medications for diabetes mellitus and hypertension. Unfortunately, few studies have examined the consequences of long-term use of weight-control medications. E Surgery Surgery may be a weight-loss option for patients who are severely obese (with a BMI of 40 or above) and suffer from serious medical complications due to weight. While the number of people in the United States who qualify for surgery remains small, the percentage of Americans with a BMI of 40 or above increased from less than 1 percent in 1990 to 2.2 percent in 2000. There are two accepted surgical procedures for reducing body weight: gastroplasty and gastric bypass. Although these two procedures use different surgical 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 also provide patients with a comprehensive program for long-term weight control. VI NEW DIRECTIONS IN WEIGHT CONTROL The weight-loss goal of most obese dieters is to achieve an ideal weight often defined by celebrities and models in fashion magazines. But research over the last decade indicates that a 5- to 10-percent reduction in body weight is sufficient to significantly improve medical conditions associated with obesity, such as hypertension, diabetes mellitus, and elevated cholesterol levels. These 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 weight-loss goals 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. Yet no obesity treatment produces long-term, maintainable weight losses significant enough for patients to reach this goal. 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, many health experts believe. Contributed By: Gary D. Foster Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.