Obesity

Obesity has recently become an epidemic in the US, with 31% of American adults classified as obese (body mass index >30kgm~2) and 68% classified as overweight (body mass index >25kgm~2) in 2000. The prevalence of obesity in childhood tripled from 5% in 1980 to 15% in 2000 according to National Health and Nutrition Examination Surveys (NHANES). There is every indication that the developed countries of Western Europe are not far behind. Indeed, obesity is becoming a worldwide problem, rapidly increasing in many developing countries including China and India, and overtaking undernutrition as the major nutritional problem.

Although obesity affects children in all socioeconomic classes, it is more prevalent in those of lower socioeconomic status in the US and developed countries, whereas it tends to affect the well-off in developing countries. This suggests that food insecurity and poor food choices are more the problem than lack of availability because of poverty. Although only 30% of obesity begins in adolescence, some estimate that 80% of obese adolescents will become obese adults, and obese adolescents are at much more risk for diabetes and major medical complications later in life. Since long-term weight loss is usually very difficult to achieve and is often unsuccessful despite widespread attempts at dieting, efforts to prevent obesity in early life are important.

Ultimately, weight gain results from dietary energy intake exceeding metabolic basal needs and activity. Only rarely is this due to some identifiable disorder of basal metabolic requirements such as hypothyroid-ism. However, it is difficult to measure either dietary intake or activity with enough accuracy to detect the relatively small mismatch necessary to add weight. For example, a small increase in dietary intake of 200kcalday_1, without a corresponding increase in activity could theoretically result in a weight gain of 8 kg over the course of a year.

Although the heritability of obesity has been estimated to be on the order of 60-80% on the basis of twin studies and family histories, the genetics of obesity are complex and just beginning to be understood. Adult weight is much more reflective of biological parents rather than adoptive parents in twin studies. Known genetic syndromes producing obesity in humans are rare (on the order of 1-2% of obese patients) but should be considered, such as trisomy 21 (Down's syndrome), Prader-Willi,

Bardet-Biedl and Beckwith-Wiedemann syndromes, hypothyroidism, and polycystic ovary syndrome.

The adipose fat cell is not only a passive storage site but an endocrinologically active secretor of many substances like leptin, adiponectin, and cyto-kines, which participate in an inflammatory response and may mediate a host of adverse consequences, including insulin resistance and diabetes. Obesity is related to an increased risk of developing type 2 insulin-resistance diabetes mellitus, hyper-lipidemia, heart disease, obstructive sleep apnea, asthma and other respiratory problems, back pain and orthopedic problems, fatty liver (nonalcoholic steato-hepatitis or NASH), gallstones, and depression. The increasing incidence of type 2 diabetes in obese adolescents is already being noticed, with estimates of 200 000 diabetics under age 20 years in the US predicted to rise to a lifetime risk of developing diabetes of 33-39% for those born in the year 2000.

The rapid increase in obesity has made standards based on population percentiles meaningless as medical obesity involved more than just the top 5% of weight-for-age. Instead of just relying on cross-sectional height- and weight-for-age graphs (see Figures 1 and 2), there has developed a need for a more valid indicator of obesity. The body mass index (BMI) charts recently released by the Centers for Disease Control allow for tracking of BMI standards for adolescents, who should have a BMI lower than the 20-25 kg m-2 expected for adults. Although long-term validation data is not as available as in adults, in adolescents obesity is considered above the 95th percentile for age, with risk for obesity defined as above 85th percentile for age.

Body mass index is defined as weight (in kilograms) divided by height (in meters) squared, and is considered the best anthropometric surrogate for body composition (see Figures 3 and 4). Waist size may be an easier measurement to follow in adults, and particularly identifies central adiposity. Measurements by tape and caliper of mid-arm circumference and triceps skinfolds have a fairly good correlation (0.7-0.8) with more expensive research methods of underwater weighing and dual-energy X-ray absorptiometry (DEXA), and can be made even more accurate by including biceps, subscapu-lar, and suprailiac skinfold measurements. Bioelectric impedance measures the difference in resistance between adipose and lean body tissue, but can be affected by fluid shifts especially in ill patients.

Physical examination should include blood pressure measurement because of the high percentage of comorbidity of the metabolic syndrome (obesity, hypertension, dyslipidemia, and/or diabetes).

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Figure 1 Weight-for-age percentiles: boys, 2-20 years. (Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion 2000: http://www.cdc.gov/growthcharts)

The metabolic syndrome is defined as three or more of the following: abdominal obesity (waist circumference greater than 40 inches (100 cm) in men or 35 inches (90 cm) in women), fasting hypertriglyceridemia (<150mgdl_1), high fasting glucose greater than 110mgdl_1, low high-density cholesterol (<40mgdl_1), and high blood pressure (>135/

85mmHg). So far, it is mostly seen in later life (>40% of those over 60), but is increasingly seen at younger ages (7% of 20-29 years old). Acanthosis nigricans is a skin hyperpigmentation, chiefly around the neck, seen in about 20% of obese patients, especially African-Americans, which reflects insulin resistance and this finding should

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Figure 2 Weight-for-age percentiles: girls, 2-20 years. (Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion 2000: http://www.cdc.gov/growthcharts)

provoke screening tests for type 2 diabetes. Laboratory screening tests might include thyroid-stimulating hormone for hypothyroidism, fasting glucose, insulin, and glycosylated hemoglobin (HbAlC) for type 2 diabetes.

Diet histories and diet recalls are particularly important in nutritional assessments, but quantitative calorie counts are particularly unreliable in obese patients because of widespread conscious and subconscious underreporting of 20% or more. Regular meetings with a dietician should involve counseling on healthy eating choices. The recommendations regarding daily activity should include hours of television watching per day or per week because this is

2 to 20 years: Boys name_

Body mass index-for-age percentiles record #

SOURCE: Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000) http://www.cdc.gov/growthcharts

Figure 3 Body mass index-for-age percentiles: boys, 2-20 years. (Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion 2000: http://www.cdc.gov/growthcharts)

SOURCE: Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000) http://www.cdc.gov/growthcharts

Figure 3 Body mass index-for-age percentiles: boys, 2-20 years. (Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion 2000: http://www.cdc.gov/growthcharts)

well correlated with obesity, not only because of decreased activity but also because of the influence of commercial snack food advertising.

Treatment should ideally involve a multidisciplin-ary team with a dietician, social worker, physical therapist, and physician, concentrating on lifestyle modification, moderate caloric restriction and regular exercise, with frequent follow-up and compliance being a good indicator of likelihood of success. Recent success with low-carbohydrate diets rather than the traditional low-fat diet advice suggests the importance of the role of satiety in maintaining caloric restriction. Most commercial diet plans promise short-term weight loss, but very few long-term studies have shown these to keep weight off for more than 6-12 months. As adolescents naturally

2 to 20 years: Girls name_

Body mass index-for-age percentiles record #

SOURCE: Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000) http://www.cdc.gov/growthcharts

SOURCE: Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000) http://www.cdc.gov/growthcharts

Figure 4 Body mass index-for-age percentiles: girls, 2-20 years. (Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion 2000: http://www.cdc.gov/growthcharts)

gain weight with height as they progress through puberty, it is probably more important that they learn healthy eating and activity habits over the long term rather than losing weight quickly only to gain it back within a few months.

Medications such as phenteramine-fenfluramine and stimulants have gained recent notoriety with unforeseen side effects. Possible treatment with leptin and other hormones or antagonists has much future promise, but so far has been effective only in rare patients with specific defects. Surgical gastro-plasty has proven the most successful long-term therapy for massively obese adults, possibly because of suppression of ghrelin, increased satiety, and reduced hunger, but morbidity and mortality is variable and the option of major surgery should be carefully considered only as a last resort before offering it to any adolescents.

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