Marcie B. Schneider
Obesity is a serious medical problem that is increasing in prevalence in the adolescent and adult population. Almost two thirds (65.7%) of adults are overweight or obese. Obesity is associated with up to 325,000 deaths/year and a shortened lifespan.
Obesity is a now a common problem among adolescents. In children and adolescents, the term obesity has been replaced by overweight. The prevalence of overweight in American adolescents ranges from 12.7% to 24.7%, depending on gender and race. It is a condition in which the psychobiological cues for eating are discordant with energy requirements. Both genetic and environmental factors contribute to overweight problems. Studies on fraternal twins raised apart suggest a strong genetic influence on body mass index (BMI). Genetic mutations have also been identified. Endocrine and metabolic causes such as hypothyroidism, hypercortisolism, and Prader-Willi syndrome occur infrequently in adolescents.
The Expert Committee on Clinical Guidelines for Overweight in Adolescent Preventive Services (Himes and Dietz, 1994) recommends screening adolescents for overweight and at risk for overweight by using the BMI. The BMI is equal to the weight in kilograms divided by the square of the height in meters:
Adolescents' body fatness changes over the years with growth and development. Teenage girls and boys differ in their body fatness as they mature. This is why BMI for adolescents, also referred to as BMI-for-age, is gender and age specific. It is an easy index to calculate and has a correlation of 0.7 to 0.8 with body fat content in adults. The correlation coefficient of BMI with body fat content is 0.39 to 0.90 in children and adolescents.
For children and adolescents, at risk for overweight is defined as a BMI between the 85th and 95th percentiles for age and gender, while overweight is defined as BMI exceeding the 95th percentile for age and gender. BMI values in adolescents are listed in Chapter 1 (Figs. 1.25 and 1.26). Chapter 4 (Figs. 4.8 and 4.9) also shows height, weight, and BMI by age and gender. BMI-for-age charts can be obtained from the Centers for Disease Control and Prevention (CDC) on their Web site: www.cdc.gov/growthcharts/.
The standards for defining obesity in adults 20 years and older were changed in 1998, following changes to the World Health Organization (WHO) definitions in 1995. This has increased the number of adults identified in the United States as being overweight or obese. The definition changed the lower limit for BMI for overweight persons from 27.8 kg/m2 in adult men and 27.3 kg/m2 in women to 25 kg/m2.
The criteria published in 1998 by the National Heart, Lung and Blood Institute (NHLBI) of the National Institutes of Health (NIH) (1998) in Clinical Guidelines for Identification, Evaluation, and Treatment of Overweight and Obesity in Adults (Archives of Internal Medicine, 1998) include the following:
Although total body fat can be measured indirectly by a variety of techniques, its use is limited to the research laboratory or clinical studies. However, a clinically useful method is the measurement of triceps skinfold thickness. Barlow and Dietz (1998) published a chart of triceps skinfold thickness for age and gender where greater than the 95th percentile suggests excessive fatness (Table 32.1).
To measure triceps skinfold, calipers are placed 1 centimeter above the midpoint between the acromion and olecranon process on the posterior (triceps area) of a relaxed right arm and measured 3 times, using the average as the thickness. This measurement does not take into account the regional distribution of body fat, which in adults has been correlated with future obesity-related health risk. Potentially useful measurements in adults older than 20 years are the waist circumference and the waist-hip ratio. Many studies have demonstrated distribution of body fat as an independent risk factor for cardiovascular disease. Visceral abdominal fat is more likely to contribute to elevated blood cholesterol and other lipid abnormalities, glucose intolerance, and hypertension. Normal values for waist circumference in children and adolescents are being studied. A recent study using these norms correlated waist circumference with risk for insulin resistance (Hirschler et al., 2005).
In summary, methods that use just height and weight are inexpensive and easy to use but do not reflect regional body fat distribution. Skinfold measurements can be inaccurate due to interobserver error. Further research on waist circumference in children and adolescents may prove to be a useful measure. The current developmentally based BMI percentile curves overcome many of the difficulties found in the past height-for-weight charts, but still do not reflect important body fat distribution characteristics.
Effects of Puberty on Body Composition
During adolescence, lean body mass increases in both sexes. The increase is greater in males because of their greater increase in skeletal muscle. The maximum increase in muscle mass occurs at about the time of peak height velocity (PHV) in both sexes, whereas the maximum fat deposition occurs 2 years before PHV. However, in females, fat deposition continues throughout puberty and females ultimately have more body fat than males.
Effects of Obesity on Puberty
Many theories have been advanced, but the cause of obesity is still unclear. Obesity is a chronic condition with multiple factors contributing to its etiology. Genetic, cultural, socioeconomic, behavioral, and situational factors all play a role in establishing dietary habits and thereby weight control. At some time in future, obesity may be divided into different disease classifications, with therapies tailored to match the underlying cause. At present, only 5% of overweight children and adolescents have an underlying cause identified. This includes approximately 3% with endocrine problems (hypothyroidism, Cushing syndrome, hypogonadism) and 2% with rare syndromes (Prader-Willi, Laurence-Moon-Biedl, Fröhlich, Alström, Kallmann).
Familial or Genetic
Activity and Energy Expenditure
There are conflicting reports regarding energy expenditure in obese individuals. Obese individuals filmed in time-lapse photography seem to move less than normal-weight individuals. Although some studies show no evidence to implicate a decrease in energy utilization in those who are overweight, Ravussin et al. (1988) found that the rates of energy expenditure were lower in obese individuals and that these rates of expenditure seem to cluster in families. Dietz (1993), drawing from longitudinal data collected in the National Health and Nutrition Examination Surveys (NHANES) study, stated that the most powerful predictor of the development of overweight in adolescence was the time that a child (6–11 years) spends viewing television, even after controlling for other known variables associated with overweight in childhood. For every extra hour of television watched by 12- to 17-year olds, there is a 2% increase in prevalence of overweight. Hernandez et al. (1999) found a 12% increase in prevalence of overweight for each hour of television watched and a 10% decrease in overweight prevalence with every hour of daily exercise in Mexican children. Recently, Epstein et al. (2005) reported that decreasing sedentary behaviors led to a decrease in energy intake, and Gutin et al. (2005) found that adolescents who regularly engaged in exercise were more likely to be fit and lean.
Caloric intake is variably elevated in overweight adolescents and is dependent on where they eat. In one study, overweight adolescent boys ingested more calories at school than at home, compared with their lean counterparts. Retrospective diet histories tend to underreport caloric intake in both overweight and nonoverweight adolescents, but more so in the overweight.
Overweight adolescents often exhibit the following behaviors:
20 years or older were estimated to be obese while in NHANES 1999 to 2002, 30.4% of adults were obese. There was a dramatic increase from prior studies in all race and sex groups.
Influence Of Obesity On Health
Complications due to obesity in adolescents include:
Future medical problems are usually not a concern of the overweight adolescent, who is more preoccupied with the psychosocial consequences. The overweight adolescent who becomes an obese adult will have more severe obesity than those adults whose obesity began in adulthood. A 50-year follow-up study of overweight adolescents found that the rate of morbidity and mortality from cardiovascular disease was significantly increased compared to their lean counterparts (Must et al., 1992). Moreover, the influence of adolescent overweight on adult morbidity and mortality was independent of the effects of adolescent overweight on adult weight. Excess weight is associated with an increased incidence of cardiovascular disease, type 2 diabetes mellitus, hypertension, stroke, dyslipidemia, sleep apnea, osteoarthritis, and some cancers. However, >80% of the mortality related to complications of obesity occurs in people with a BMI >30 kg/m2.
Medical evaluation includes the assessment of factors that contribute to weight gain, inhibit weight loss, and comorbid factors that exist and can benefit from weight loss or maintenance.
Therapy for obesity is a challenge for both the health care provider and the patient of any age. Young adolescents are often more difficult to treat than older adolescents because of the lack of abstract thought and motivation. In general, treatment focuses on control rather than cure, as is so often the case with chronic medical conditions. When is it appropriate to strongly recommend weight reduction? Certainly, adolescents with morbid obesity (those with twice normal weight, BMI >40 kg/m2, or >100 lb [45.5 kg] overweight) are at significant risk for medical problems and need to be encouraged to lose weight. The weight goal should be <85% BMI for age and sex. For many adolescents this can be accomplished by weight maintenance over a period of time, whereas for others a slow 1 lb/month weight loss should be encouraged. It is essential to remember that severe caloric restriction during adolescence, particularly during a growth spurt can halt growth and the progression of puberty. Therefore, understanding where an adolescent is with respect to his or her pubertal development and more specifically to their growth spurt, is critical in developing appropriate weight goals.
Critical areas in assessing treatment readiness in the adolescent include:
Diet, exercise, behavior modification, and support are still the mainstay of treatment for obesity in adolescents and young adults. The role of medication and bariatric surgery for overweight adolescents is still being evaluated.
An energy deficit is needed for active weight loss and is a critical part of management. However, diet alone is rarely successful in achieving permanent weight loss. Predicting weight loss for an individual teenager based on caloric intake is difficult and can vary widely. For older adolescents and young adults, a deficit of 250 to 500 kcal/day is associated with a loss of approximately 0.5 to 1 lb/week (0.23–0.45 kg). Greater caloric restrictions are very difficult to maintain. The type of caloric restriction should be well planned and should take into account current food types and intake, eating habits, situation-dependent eating, and family and cultural preferences. To support normal growth and development, there must always be good nutritional balance among the food groups.
Approximate daily energy needs in the postpubertal adolescent can be calculated from the weight in kilograms
(W) as follows:
The activity factor is 1.2 for a low activity level, 1.4 for a moderate activity level, or 1.6 for a high activity level. The energy requirement to maintain each extra kilogram of body weight is approximately 22 kcal. Therefore, an adolescent who weighs 20 kg more than another needs an additional 440 kcal to maintain that weight.
Various nutritional approaches to weight loss exist and some have been studied. The ketogenic diet or low-carbohydrate diet has been studied in adolescents. Sondike et al. (2003)published a 12-week randomized controlled trial comparing a low-fat diet to a low-carbohydrate diet in adolescents. The low-carbohydrate diet was effective for short-term weight loss without affecting the lipid profile. However, the sample size was small with a brief follow-up period. This diet has not been studied in younger adolescents and the long-term benefits require further study.
A balanced weight reduction diet focusing on healthy lifestyle practices is recommended for the adolescent population and should include the following:
One simplification of this diet is the “Traffic Light” approach (Epstein et al., 1998). Green light foods can be eaten freely (nonfat foods, low-fat foods, fruits, vegetables). Yellow light foods are those eaten with caution (low-to-moderate fat foods such as breads, pastas). Red light foods are those to be eaten rarely (nuts, candy). This concrete view can be helpful to both children and adolescents.
Every weight reduction program should include an increase in physical activity. This can include the following:
Cognitive Behavioral Therapy or Behavior Modification Techniques
Cognitive behavioral therapy (CBT) or behavior modification techniques can be effective when used in combination with diet and medical therapies. Penich et al. (1971) and Stunkard et al. (1970) have reviewed this approach. These programs usually contain several components:
Group participation as part of the weight-loss program may be beneficial. Groups provide encouragement, support, and an opportunity for release of feelings, peer contact, and acceptance.
Although there is no evidence for the effectiveness of structured commercially based weight-loss programs in adolescents, such programs have been shown to provide modest weight loss compared with self-help groups in adults (Heshka et al., 2003). All the structured commercial weight-loss programs studied (ranging from moderately to very restrictive diets) led to a similar amount of weight loss at 1 year, with poor dietary adherence with the more restrictive diets (Dansinger et al., 2005).
Medications for the Treatment of Obesity
The two medications studied in the treatment of adolescent obesity are sibutramine and orlistat. A meta-analysis of pharmacological treatments of adult obesity is available from Li et al. (2005).
Contraindications include anorexia nervosa, hypersensitivity to drug, therapy with monoamine oxidase inhibitors or other serotonergic drugs, coronary heart disease, congestive heart failure, stroke, arrhythmia, uncontrolled hypertension, severe hepatic or renal disease, pregnancy, and lactation. Caution is advised in individuals with a history of seizures. This medication is not indicated for mildly or moderately overweight individuals in the absence of medical complications.
Finally, many of the selective serotonin reuptake inhibitors (SSRIs), including fluoxetine, fluvoxamine, sertraline, and citalopram have been used to decrease binging in patients with binge eating disorder. Sibutramine and topiramate have been found to decrease binging in this population as well.
Gastrointestinal Procedures: Bariatric Surgery
A multidisciplinary group of pediatric and surgical specialists published guidelines for bariatric surgery in adolescents (Inge et al., 2004). Potential candidates include:
Those with BMI >50 kg/m2 with less serious comorbid conditions could be considered. A multidisciplinary team including the bariatric surgeon and specialists in adolescent obesity, psychology, and nutrition are essential to the process. Potential procedures include Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding. The Roux-en-Y gastric bypass is performed laparoscopically, separating the stomach into a small-volume upper pouch (limiting oral intake) and connects the stomach to a limb of jejunum. Approximately 85% of individuals lose at least 50% of their excess weight at 4 years. Micronutrient supplementation is needed. The laparoscopic adjustable band uses a small silastic band around the upper stomach that is inflated with saline through a subcutaneous port. Although reversible and removable, there have been technical issues as well as patient management problems. A meta-analysis of surgical treatment of obese adults is available from Maggard et al. (2005).
Although similar guidelines are not available for adolescents, the American College of Physicians published evidence-based practice guidelines for the treatment of obesity in adults (Snow et al., 2005). The following are the recommendations:
For Teenagers and Parents
http://www.health.gov/dietaryguidelines/. Dietary guidelines.
http://win.niddk.nih.gov/. Weight-control Information Network (WIN), national information service of the NIH, National Institute of Diabetes and Digestive and Kidney Diseases.
http://www.nhlbi.nih.gov/health/public/heart/hbp/dash. DASH, the Dietary Approaches to Stop Hypertension.
http://www.shapeup.org/sua. Shape up America! Founded by former Surgeon General Everett Koop, M.D., promoting healthy weight and increased physical exercise.
http://www.usda.gov/cnpp. Center for Nutrition Policy and Promotion.
http://www.eatright.org. American Dietetic Association Web site for nutrition information, food pyramid and good nutrition reading list
http://www.kidshealth.org/teen/food fitness/dieting/obesity.html. Information for teens reviewed by physicians, sponsored by Nemours Foundation.
http://www.kidshealth.org/parent/nutrition_fit/nutrition/overweight_obesity.html. Information for parents, reviewed by physicians, sponsored by Nemours Foundation.
http://www.aap.org/obesity/family.htm. Information for parents on childhood obesity.
http://www.bam.gov. CDC Web site for teens on health issues including obesity and nutrition.
For Health Professionals
http://www.nhlbi.nih.gov/guidelines/obesity/ob_home.htm. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, from NIH.
http://www.niddk.nih.gov/health/nutrit/nutrit.htm. National Institute for Diabetes and Digestive and Kidney Diseases, publications on weight control. http://www.aafp.org/afp/990215ap/861.html. From American Family Physician, evaluation and treatment of childhood obesity.
http://www.obesity.org/subs/childhood/. American Obesity Association.
http://www.aap.org/obesity. Resources for physicians on obesity.
http://www.nasso.org. The obesity society, a scientific society for research, education, advocacy and organizational development whose journal is Obesity Research.
http://www.obesityonline.org. Online collection of evidence based obesity education resources.
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