Obesity was traditionally defined as a weight at least 20% above the weight corresponding to the lowest death rate for individuals of a specific height, gender, and age. This weight was designated as the ideal weight. Twenty to forty percent over ideal weight was considered mildly obese; 40-100% over ideal weight was considered moderately obese; and 100% over ideal weight was considered grossly, or morbidly, obese.
Current guidelines for obesity use a measurement called the body mass index (BMI). The BMI uses height and weight to compare the ratio of body fat to total body mass. Calculating BMI requires only two measurements: weight and height. To calculate BMI using metric units, weight in kilograms (kg) is divided by the height squared measured in meters (m). To calculate BMI in English units, weight in pounds (lb) is divided by height squared in inches (in) and then multiplied by 703. This calculation produces a number that is the individual's BMI. This number, when be compared to the statistical distribution of BMIs for the adults ages 20-29, indicates whether the individual is underweight, average weight, overweight, or obese. The 20-29 age group was chosen as the standard because it represents fully developed adults at the point in their lives when they statistically have the least amount of body fat. Body fat is ideally about 15% of total body mass for the adult male and about 20-25% for the for the adult female. One criticism of the BMI is that it does not distinguish between fat and muscle. A simple BMI calculator can be found at http://www.nhlbisupport.com/bmi .
For adults, the BMI is age and gender independent. All adults age 20 and older are evaluated on the same 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
For children and teens, the BMI is calculated in the same was as it is for adults, but the results are interpreted differently. Instead assigning a child to a specific weigh category based on their BMI, a child's BMI is compared to that of other children of the same age and sex. Children are then assigned a percentile based on their BMI. The percentile tells them how their weight compares to that of other children who are their age and gender. For example, if a girl is in the 75th percentile for her age group, 75 of every 100 children who are her age weigh less than she does and 25 of every 100 weigh more than she does. Obese is not an official category designation for children because of its negative image. The weight categories for children are:
Below the 5th percentile: Underweight
5th percentile to less than the 85th percentile: Healthy weight
85th percentile to less than the 95th percentile: At risk of overweight
95th percentile and above: Overweight
Measurements and comparisons of waist and hip circumference can also provide some information regarding risk factors associated with weight. The higher the ratio, the greater the chance for weight-associated complications. Calipers can be used to measure skin-fold thickness on the back of the arm to determine whether tissue is muscle (lean) or adipose tissue (fat).
Obesity is a serious public health problem in the United States and other developed countries. By 2007, it had become apparent that obesity was also increasing rapidly in some developing countries also. According to the United States Centers for Disease Control and Prevention (CDC), between the mid-1970s and the mid-2000s, the percentage of overweight and obese American adults aged 20-74 years increased from 15.0% to 32.9%. During this same time, the percentage of overweight children ages 2-5 years increased from 5.0% to 13.9% and for children aged 6-11 years from 6.5% to 18.8%. Overweight and obesity in teens increased from 5.0% to 17.4%. In 2007, the World Health Organization (WHO) estimated that 1.6 billion people over age 15 were overweight and at least 400 million were obese.
Excess 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 colon, prostate, endometrial, and, possibly, breast cancer. The cost of obesity to the United States economy in 2006 was estimated at about $dollar100 billion, of which [dollar]52 billion were in direct health care costs and [dollar]33 billion were in weight-loss products and services.
Causes and symptoms
The reason 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). Studies of adoptees confirm this relationship--the majority of adoptees followed a pattern of weight gain that more closely resembled that of their birth parents than their adoptive parents. A genetic predisposition to weight gain, however, does not automatically mean that a person will be obese. Eating habits and patterns of physical activity also play a significant role in the amount of weight a person gains. Recent 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. Carbohydrates (e.g., cereals, breads), fruits, vegetables, and protein (fish, lean meat, turkey breast, skim milk) are converted into fuel almost as soon as they are consumed. Most fat calories are immediately stored in fat cells, which add to the body's weight and girth as they expand and multiply. A sedentary lifestyle, particularly prevalent in affluent societies, such as in the United States, can contribute to weight gain. Psychological factors, such as depression and low self-esteem may, in some cases, also play a role in weight gain.
The stage of life at which a person becomes obese can affect his or her ability to lose weight. In childhood, excess calories are converted into new fat cells (hyperplastic obesity), while excess calories consumed in adulthood 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.
Obesity can also be a side effect of certain disorders and conditions, including:
Cushing's syndrome, a disorder involving the excessive release of the hormone cortisol
hypothyroidism, a condition caused by an underactive thyroid gland
neurologic disturbances, such as damage to the hypothalamus, a structure located deep within the brain that helps regulate appetite
consumption of such drugs as steroids, antipsychotic medications, or antidepressants
The major symptoms of obesity are excessive weight gain and the presence of large amounts of fatty tissue. Obesity can also give rise to several secondary conditions, including:
arthritis and other orthopedic problems, such as lower back pain
high cholesterol levels
high blood pressure
menstrual irregularities or cessation of menstruation (amenorhhea)
decreased fertility, and pregnancy complications
shortness of breath that can be incapacitating
sleep apnea and sleeping disorders
skin disorders arising from the bacterial breakdown of sweat and cellular material in thick folds of skin or from increased friction between folds
emotional and social problems
Diagnosis of obesity is made by observation and by calculating the individual's BMI. Physicians may also obtain direct measurements of an individual's body fat content by using calipers to measure skin-fold thickness at the back of the upper arm and other sites. The most accurate means of measuring body fat content involves immersing a person in water and measuring relative displacement; however, this method is impractical and is usually only used in scientific studies requiring very specific assessments.
Doctors may also note how a person carries excess weight on his or her body. Studies have shown that this factor may indicate whether an individual has a predisposition to develop certain diseases or conditions that may accompany obesity. "Apple-shaped" individuals who store most of their weight around the waist and abdomen are at greater risk for cancer, heart disease, stroke, and diabetes than "pear-shaped" people whose extra pounds settle primarily in their hips and thighs.
Treatment of obesity depends primarily on how overweight a person is and his or her overall health. However, to be successful, any treatment must produce life-long behavioral changes rather than short-term weight loss. "Yo-yo" dieting, in which weight is repeatedly lost and regained, has been shown to increase a person's likelihood of developing fatal health problems than if the weight had been lost gradually or not lost at all. Behavior-focused treatment should concentrate on:
what and how much a person eats. This aspect may involve keeping a food diary and developing a better understanding of the nutritional value and fat content of foods. It may also involve changing grocery-shopping habits (e.g., buying only what is on a prepared list and only going on a certain day), timing of meals (to prevent feelings of hunger, a person may plan frequent, small meals), and actually slowing down the rate at which a person eats.
how a person responds to food. This may involve understanding what psychological issues underlie a person's eating habits. For example, one person may binge eat when under stress, while another may always use food as a reward. In recognizing these psychological triggers, an individual can develop alternate coping mechanisms that do not focus on food.
how they spend their time. Making activity and exercise an integrated part of everyday life is a key to achieving and maintaining weight loss. Starting slowly and building endurance keeps individuals from becoming discouraged. Varying routines and trying new activities also keeps interest high.
For most individuals who are mildly obese, these behavior modifications entail life-style changes that they can make independently while being supervised by a health care professional. Other mildly obese persons may seek the help of a commercial weight-loss program (e.g., Weight Watchers). The effectiveness of these programs is difficult to assess, since programs vary widely, dropout rates are high, and few employ members of the medical community. However, programs that emphasize realistic goals, gradual progress, sensible eating, and exercise can be very helpful and are recommended by many doctors. Programs that promise instant weight loss or feature severely restricted diets are not effective and, in some cases, can be dangerous.
Body/mass index (BMI) chart
Body/mass index can be calculated by locating your height and weight on the chart and drawing a diagonal line between the two. Where the line crosses over the third bar is the approximate BMI.
(Illustration by Argosy Inc.)
For individuals who are moderately obese, medically supervised behavior modification and weight loss are required. While doctors will put most moderately obese patients on a balanced, low-calorie diet (1200-1500 calories a day), they may recommend that certain individuals follow a very-low-calorie (400-700 calories) diet under medical supervision for as long as three months. This therapy, however, should not be confused with commercial liquid protein diets or commercial weight-loss shakes and drinks. Doctors tailor these very-low-calorie diets to specific patients, monitor patients carefully, and use them for only short periods. In addition to reducing the amount and type of calories consumed by the patient, doctors will recommend professional therapists or psychiatrists who can help the individual effectively change his or her behavior in regard to eating.
For individuals who are severely obese, dietary changes and behavior modification may be accompanied by surgery to reduce or bypass portions of the stomach or small intestine. The branch of medicine that deals with the study and treatment of obesity is known as bariatrics, and weight loss surgery is sometimes called bariatric surgery. Although obesity surgery is less risky as of 2007 because of recent innovations in equipment and surgical technique, it is still performed only on patients for whom other strategies have failed and whose obesity seriously threatens their health. Other surgical procedures are not recommended, including liposuction, a purely cosmetic procedure in which a suction device is used to remove fat from beneath the skin, and jaw wiring, which can damage gums and teeth and cause painful muscle spasms.
Appetite-suppressant drugs are sometimes prescribed to aid in weight loss. These drugs work by increasing levels of serotonin or catecholamine, which are brain chemicals that control feelings of fullness. Appetite suppressants, though, are not considered truly effective, since most of the weight lost while taking them is usually regained after stopping them. Also, patients can potentially abuse suppressants containing amphetamines. While most of the immediate side effects of these drugs are harmless, the long-term effects of these drugs, in many cases, are unknown. Two drugs, dexfenfluramine hydrochloride (Redux) and fenfluramine (Pondimin) as well as a combination fenfluramine-phentermine (Fen/Phen) drug, were taken off the market when they were shown to cause potentially fatal heart defects. In November 1997, the United States Food and Drug Administration (FDA) approved a new weight-loss drug, sibutramine (Meridia). Available only with a doctor's prescription, Meridia can significantly elevate blood pressure and cause dry mouth, headache, constipation, and insomnia. Patients with a history of congestive heart failure, heart disease, stroke, or uncontrolled high blood pressure should not use this medication. In 2007, xenical (Alli), formerly a prescription weight-loss drug, became the first over-the-counter (nonprescription) drug approved for weight loss by the United States Food and Drug Administration (FDA). Other weight-loss medications are available with a doctor's prescription.
Phenylpropanolamine (Acutrim, Dex-A-Diet, Dexatrim, Phenldrine, Phenoxine, PPA, Propagest, Rhindecon, Unitrol) was a component of many nonprescription weight-loss drugs and cold or cough. It was removed from approved by the FDA because it increased the risk of stroke.
Prescription medications or over-the-counter weight-loss products can cause:
Ephedra is genus of plants found worldwide. One species, E. sinica or Chinese ephedra, has a long history of use in complementary and alternative medicine (CAM). In the late twentieth century, ephedra gained popularity as a weight-loss supplement. The herb can cause life-threatening side effects, and since April 2004, sale of products containing ephedra have been banned in the United States. In Traditional Chinese Medicine (TCM) ephedra is called ma huang.
Diuretic herbs, which increase urine production, can cause short-term weight loss but cannot help patients achieve lasting weight control. The body responds to heightened urine output by increasing thirst to replace lost fluids, and patients who use diuretics for an extended period eventually start retaining water again anyway. In moderate doses, psyllium, a mucilaginous herb available in bulk-forming laxatives like Metamucil, absorbs fluid and makes patients feel as if they have eaten enough. Red peppers and mustard help patients lose weight more quickly by accelerating the metabolic rate. They also make people thirstier, so they crave water instead of food. Walnuts contain serotonin, the brain chemical that tells the body it has eaten enough. Dandelion (Taraxacum officinale ) can raise metabolism and counter a desire for sugary foods.
Acupressure and acupuncture can also suppress food cravings. Visualization and meditation can create and reinforce a positive self-image that enhances the patient's determination to lose weight. By improving physical strength, mental concentration, and emotional serenity, yoga can provide the same benefits. Also, patients who play soft, slow music during meals often find that they eat less food but enjoy it more.
Getting the correct ratios of protein, carbohydrates, and good-quality fats can help in weight loss via enhancement of the metabolism. Support groups that are informed about healthy, nutritious, and balanced diets can offer an individual the support he or she needs to maintain this type of eating regimen.
Keeping lost weight off permanently is a difficult challenge. As many as 85% of dieters who do not exercise on a regular basis regain their lost weight within two years. In five years, the figure rises to 90%. Repeatedly losing and regaining weight (yo yo dieting) encourages the body to store fat and may increase a patient's risk of developing heart disease. The primary factor in achieving and maintaining weight loss is a life-long commitment to regular exercise and sensible eating habits.
Obesity experts suggest that a key to preventing excess weight gain is monitoring fat consumption along with counting calories. In the early twenty-first century fat replacers began to be added to many foods. Fat replacers, also called fat substitutes, are substances that take the place of all or some of the fat in a food and yet give the food a taste, texture, and mouth feel that is similar to the original full-fat food. They reduce the amount of fat in food, and they usually reduce the calorie content of the food. As of 2000, there were more than 5000 reduced-fat foods on the market. New reduced- and low-fat foods were being introduced at the rate of about 1,000 per year. It is not clear what effect fat replacers will have on long-term weight loss.
The United States Department of Agriculture (USDA) food pyramid, called MyPyramid (http://www.mypyramid.gov ) to distinguish it from earlier versions, contains recommendations on diet and exercise based on the Dietary Guidelines for Americans 2005. Recommendations are based on the individual's BMI. MyPyramid makes recommendations in seven categories: grains, vegetables, fruits, milk, meat and beans, oils, discretionary calories, and physical activity. MyPyramid assumes that people will eat from all food categories. The personalized recommendations about quantities to eat for each group do not take into consideration special diets for people with diabetes or other diseases.
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 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. Exercise increases the metabolic rate by creating muscle, which burns more calories than fat. When regular exercise is combined with regular, healthful meals, calories continue to burn at an accelerated rate for several hours. Finally, encouraging healthful habits in children is a key to preventing childhood obesity and the health problems that follow in adulthood.
New directions in obesity treatment
The rapid rise in the incidence of obesity in the United States has prompted researchers to look for new treatments. One approach involves the application of antidiabetes drugs to the treatment of obesity. Another field of obesity research is the study of hormones, particularly leptin, which is produced by fat cells in the body, and ghrelin, which is secreted by cells in the lining of the stomach. Both hormones are known to affect appetite and the body's energy balance. Leptin is also related to reproductive function, while ghrelin stimulates the pituitary gland to release growth hormone. Further studies of these two hormones may lead to the development of new medications to control appetite and food intake.
An alternative approach to obesity involves research into the social factors that encourage or reinforce weight gain in humans. Researchers are looking at such issues as the advertising and marketing of food products, media stereotypes of obesity, the effect of friends and family on body image, the development of eating disorders in adolescents and adults, and similar psychosocial questions.
Adipose tissue Fat tissue.
Appetite suppressant Drug that decreases feelings of hunger. Most work by increasing levels of serotonin or catecholamine, chemicals in the brain that control appetite.
Bariatrics The branch of medicine that deals with the prevention and treatment of obesity and related disorders.
Ghrelin A recently discovered peptide hormone secreted by cells in the lining of the stomach. Ghrelin is important in appetite regulation and maintaining the body's energy balance.
Hyperlipidemia Abnormally high levels of lipids in blood plasma.
Hyperplastic obesity Excessive weight gain in childhood, characterized by the creation of new fat cells.
Hypertension High blood pressure.
Hypertrophic obesity Excessive weight gain in adulthood, characterized by expansion of already existing fat cells.
Ideal weight Weight corresponding to the lowest death rate for individuals of a specific height, gender, and age.
Leptin A protein hormone that affects feeding behavior and hunger in humans. At present it is thought that obesity in humans may result in part from insensitivity to leptin.
For More Information
Apple, Robin F. James Lock, and Rebecka Peebles. Is Weight Loss Surgery Right for You? New York: Oxford University Press, 2006.
Beers, Mark H., MD, and Robert Berkow, MD, editors. "Nutritional Disorders: Obesity." Section 1, Chapter 5. In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
American Council for Fitness and Nutrition. P.O. Box 33396, Washington, DC 20033-3396. Telephone: (800) 953-1700 Web site:. http://www.acfn.org
American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, Illinois 60606-6995. Telephone: (800) 877-1600. Web site: http://www.eatright.org .
American Obesity Association. 1250 24th Street, NW, Suite 300, Washington, DC 20037. Telephone: (202) 776-7711. Fax: (202) 776-7712. Web site: http://www.obesity.org .
American Society for Bariatric Surgery. 100 SW 75th Street, Suite 201, Gainesville, FL 32607. Telephone: (866) 471-2727. Web site: http://www.asbs.org .
United States Department of Agriculture. 1400 Independence Avenue, S.W., Room 1180, Washington, DC 20250. Web site: http://www.usda.gov/wps/portal/usdahome .
Weight-control Information Network (WIN). 1 WIN Way, Bethesda, MD 20892-3665. Telephone: (877)946-4627 or (202) 828-1025. Fax: (202) 828-1028. Web site:
Medline Plus. "Obesity." U. S. National Library of Medicine, July 31 2007. http://www.nlm.nih.gov/medlineplus/obesity.html .
Uwaifo, Gabriel I. and Elif Arioglu. "Obesity." eMedicine.com, June 16, 2006. lt;http://www.eMedicine.com/med/topic1653.htm> .
United States Department of Agriculture. "Finding the Way to a Healthier You: Based on the Dietary Guidelines for Americans," 6th ed. 2005. http://www.healthierus.gov/dietaryguidelines
United States Department of Agriculture. "MyPyramid: Steps to a Healthier You." 2005. http://www.mypyramid.gov
United States Department of Health and Human Services and the United States Department of Agriculture. "Dietary Guidelines for Americans 2005." January 12, 2005. http://www.healthierus.gov/dietaryguidelines
United States Department of Agriculture. "My Pyramid for Kids." 2005. http://www.mypyramid.gov/kids/index.html
Synopsis: Rosalyn Carson-DeWitt, M.D. Rebecca J. Frey, Ph.D. Tish Davidson, A. M. Jacqueline L. Longe
Source Citation: "Obesity." Rosalyn Carson-DeWitt, M.D., Rebecca J. Frey, Ph.D., and Tish Davidson, A. M. The Gale Encyclopedia of Medicine. Ed. Jacqueline L. Longe. 3rd ed. Detroit: Gale, Online update, 2007. 5 vols.
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