Obesity in childhood and adolescence is one of the most serious nutritional problems facing the United States today. The prevalence of overweight children has increased by over 50% in the past two decades. The most recent data from 1990 indicates that 22% of children and adolescents are overweight. The highest percentages are among non-Hispanic Black girls and Hispanic boys at 30% and 27%, respectively.
Obesity relates to excess body fat. In adults, body mass index (BMI) is used to define obesity. BMI is calculated by dividing one's weight in kilograms by one's height in meters squared (kg/m2). BMI is used because it provides a reasonable estimate of adiposity (body fatness), and it relates to adverse health outcomes. Obesity in adults is defined as a BMI greater than 30 because a BMI greater than 30 is associated with an increased risk of medical problems.
In children, the medical side effects of obesity often are not readily apparent. Consequently, deciding how to define obesity in childhood has been somewhat difficult. The International Task Force on Obesity recently suggested that BMI should be used to screen for childhood obesity. BMI in children has been shown to correlate with such complications as high blood pressure, high cholesterol, diabetes, and persistence of obesity into adulthood.
The specific BMI cutoff points have not yet been established, but it will probably approximate the 85th and the 95th percentiles. For example, children who have a BMI greater than the 95th percentile for their age and their gender are considered obese (see Figure). Children who have a BMI between the 85th and the 95th percentiles are also overweight but are not defined as obese until they are greater than the 95% percentile.
There are very few medical causes of obesity in childhood. Hormonal abnormalities that lead to increased weight gain in children typically are associated with short stature or poor height growth. Examples of such conditions include hypothyroidism, Cushing's syndrome, or growth hormone deficiency. Consequently, an overweight child who has normal height growth is unlikely to have one of these hormonal abnormalities.
There are several genetic syndromes that are associated with obesity; however, these conditions generally have short stature as a coexisting finding. Additionally, developmental delays and unusual physical features commonly are part of these syndromes. A doctor can rule out the majority of syndromes and hormonal disorders by performing a careful history and a physical examination. Occasionally, blood tests or radiological examinations are performed as part of an evaluation.
The majority of obese children do not have a recognizable syndrome or a hormonal abnormality. Therefore, to understand the various proposed causes of weight gain in children, one should be familiar with the following energy balance equation:
Energy stored equates to weight gain, and energy intake is calories consumed from food and beverages. Energy expenditure is composed primarily of one's basal metabolic rate (the number of calories expended just to lie still and the major component of total energy expenditure) and energy expended for activity.
Consequently, if one's energy intake exceeds energy expenditure, weight gain occurs. An individual gains 1 pound of weight for approximately every 3,500 excess calories. Consequently, an extra 10 ounces of juice or can of soft drink (at 150 calories each) every day would amount to a weight gain of 15 pounds per year.
Most individuals regulate their body weight so precisely that it only fluctuates by about one-half pound per year. This is because each person has his/her own "set point" for body weight, and various metabolic pathways in the body defend this set point. Changes in appetite and metabolic rate occur in response to weight gain or loss, thereby "driving" weight back to its "set point."
For example, overweight individuals who lose weight may have lower resting metabolic rates than lean individuals, so they would need to eat less to maintain their reduced weight. This may be one reason why diets have such a high failure rate.
Children who have overweight parents are more likely to be overweight themselves. This observation suggests that individuals can inherit certain genes that make them susceptible for weight gain. Studies indicate that genetic factors determine up to 75% of our body weight. Thus, an individual who inherits a low basal metabolic rate may be susceptible to increased weight gain. Genes also may affect energy intake by determining specific feeding behaviors and food preferences.
Given that the genes in our population have not dramatically changed over the past several decades, genetic factors alone cannot explain the rise in obesity. Rather, it is the interaction between a genetic predisposition and an environment that is conducive to weight gain. Our technically advanced society-boasting energy-saving devices and convenient, high calorie foods-has led to changes in both activity and eating patterns.
People have increased their dining at restaurants, visiting of fast-food chains, and buying of prepared grocery items. Meals at restaurants tend to be very caloric because they are served in large portions, and they are high in fat and calories (see Table). We are led to believe that super sizes are a great deal because of the financial discount; however, they are not such a great deal in regard to the gain in calories.
|Table. Approximate Calorie Content of Fast-Food Items|
|Chicken nuggets (6 pieces)||290|
|Small french fries||250|
|Chocolate Shake (12 oz.)||440|
|Pepperoni pizza (2 slices)||500|
Additionally, most schools serve lunches that are high in fat and include choices from fast-food chains. Currently, there is no evidence that children are born with a preference for high fat foods. Rather, experts believe that liking certain foods is learned through repeated experiences with such foods. Observing what and how their parents eat also may shape children's food preferences. Parents are role models; consequently, if they like to eat high fat food, their children will likely do the same.
Spontaneous, as well as intentional, physical activity has decreased in children. Participation in school physical education classes has declined significantly; a recent survey indicated that approximately 50% of high school students were not enrolled in regular physical education classes. Children also are spending their time out of school in sedentary activities, such as watching television and playing computer games.
Several cross-sectional studies report a direct association between the amount of television watched to the degree of childhood obesity. Watching television not only limits the time for exercise and vigorous activity, but also encourages snacking and consumption of high fat foods through advertisements. Parental concerns over safety also may contribute to decreased activity in children, as their neighborhoods may not be perceived safe enough to play outside.
Lastly, children of non-active parents tend to be less active themselves. Consequently, like the modeling of eating patterns, parents may be modeling sedentary activities and reliance on labor-saving devices. The positive aspect of these environmental factors is that they are, unlike genetic factors, modifiable.
Although the majority of weight-related problems are not seen until later on in life, an overweight child may have complications that are evident. It is important for an obese child to be evaluated for the potential consequences outlined below.
Cardiovascular Disease - Many children who are overweight have elevated blood pressures (hypertension), high cholesterol, and high triglycerides. These conditions are more likely to be seen in an overweight child whose family history is positive for cardiovascular disease, hypertension, or high cholesterol.
Endocrine - Although there is rarely an endocrine cause of obesity in childhood, there are several endocrine side effects. Overweight children often have accelerated height growth; therefore, during childhood, they are tall compared to their peers. This growth acceleration appears to be a normal result of over-nutrition, and it is actually a reassuring finding, as it eliminates the majority of pathologic causes of obesity. The timing of puberty may occur on the early side in overweight children.
Adolescent girls who are overweight may experience menstrual irregularities, including infrequent or absent periods. Many young women who have polycystic ovarian syndrome are overweight. Irregular menstrual periods, acne, and/or excess body hair characterize this disorder. Lastly, many overweight children have evidence of insulin resistance. Insulin is a hormone produced by the pancreas, permitting glucose to be transported from the blood to the cells of the body.
Insulin resistance can contribute to high cholesterol and triglyceride levels. Overweight children who have insulin resistance have an increased incidence of developing diabetes mellitus in adolescence, especially when there is a family history of diabetes. In many individuals, thickening and darkening of the skin (called acanthosis nigricans) in such areas as the neck, the underarms, and the elbows are signs of insulin resistance.
Orthopedic - Because of the extra weight that they must carry, overweight children are at an increased risk for orthopedic problems. Children may complain of leg and ankle pain that is due to stresses in the joints. In younger children, bowing of the legs may occur.
Gastrointestinal - Obesity in children can lead to fatty deposits in the liver. Although this rarely causes any health problems, there can be scarring and damage to the liver in severe cases. Gallstones also are associated with obesity; however, the incidence of this complication is much higher in obese adults.
Pulmonary - Overweight children may have obstructive sleep apnea, a condition that occurs when there is an obstruction in the upper airway, making breathing difficult during sleep. In overweight children, the obstruction may be due to fat deposits in the walls of the upper airway and by the increased work of breathing that results from fat in the abdomen and the chest. Obstructive sleep apnea may impair learning and memory function in children. It also can cause excess daytime sleepiness, which may lead to an increase in sedentary activity and further weight gain.
Psychological - The greatest costs of childhood obesity may be psychological. Young children may be teased because of their weight, and they may have difficulty making friends. Because they tend to be taller, obese children may be perceived as being older than they really are and may have unrealistic expectations placed on them. Self-concept may be low in an overweight child, especially during adolescence. How a child deals with these negative attitudes is in part related to how their parents feel about him/her. If parents accept their child regardless of his/her weight and focus on positive attributes, their child is more likely to have a positive self-concept.
Persistence - Although not an immediate consequence, the risk of childhood obesity persisting into adulthood is important, as there are serious medical complications associated with being an overweight adult. The risk persistence depends on the child's age, gender, and degree of overweight. Studies indicate that 25% of overweight preschool children versus 80% of overweight adolescents will become obese adults. Adolescent girls, in particular, appear to have a greater risk than boys. Additionally, the more overweight a child is at any age, the likelihood of obesity persisting into adulthood is higher.
An overweight child should be evaluated to determine if there is a pathologic cause for his/her weight gain and if there are any weight-related health problems. A primary care doctor should begin this evaluation, and he/she will decide if laboratory tests and/or a referral to a specialist are indicated. Treatment of obesity depends on the age of the child, the degree that the child is overweight, and the family's or the child's willingness to change. A successful treatment plan includes dietary, physical activity, and behavior modification components. It is important that all family members are involved and are willing to make necessary changes themselves.
Treatment can be implemented through a primary care doctor or a structured weight control program. Initial goals should be small, so that the family and the child are not overwhelmed or discouraged. In a moderately overweight or very young child, weight maintenance, rather than weight loss, may be the goal, as the child is growing in height and thus may "grow into" a more normal BMI.
Dietary - Diets that focus on eliminating specific nutrients have not been studied extensively in children. Consequently, it is recommended that changes be made in a step-wise manner to decrease the fat and the calorie content of the diet. A nutritionist often is helpful in evaluating a child's eating patterns and in educating families how to make healthy low calorie choices. A child's diet should be analyzed, with particular attention to the amount of juice and soft drink consumption, frequency of eating outside the home, school lunches, portion sizes, and snacking.
Juice and soft drinks alone can account for a significant amount of extra calories each day. For young children, it is the parents' responsibility to determine when and how many times a child eats and what food is offered. The child's responsibility is to decide how much he/she wants to eat (within reason). If the child does not like what is offered, the parents' job is not to find something the child will eat. "Short order cooking" does not encourage children to learn about new foods, such as fruits and vegetables.
Activity - Exercise, in addition to dietary changes, is recommended for optimal weight management. The most important factor in choosing an activity or an exercise program is finding something that the child likes to do. Children are more likely to participate in an activity that they, rather than their parents, choose. The activity does not need to be an organized sport, but any type of activity or play that is sustained. For example, walking the dog, playing outside with friends, and riding a bike are all beneficial. Limiting sedentary activities (e.g., television and computer time) is very important, as this will increase a child's activity level.
Behavior Modification - Various behavior modification techniques may help a child be successful in achieving weight management goals. Self-monitoring by keeping diet and activity records enables an older child to be more aware of his/her eating and activity patterns. To provide a "safe" environment, parents should limit the amount of high calorie foods in the house, discourage eating in front of the television, and serve age-appropriate portion sizes.
Having scheduled meals and snack times and eliminating between-meal eating is in everyone's best interest. Decreasing the frequency of meals eaten outside the home and sending a bag lunch to school also are ways to make a healthier diet. Modification of eating habits may include taking smaller bites, chewing food longer, and putting the fork down between bites with the goal of increasing meal/snack duration to at least 15 minutes. Reinforcements and rewards for achieving weekly dietary and activity goals also may be helpful.
There are many medications that have been used successfully in adults to aid with weight loss; however, the Food and Drug Administration has not approved these medications for use in children. At this time, medications for childhood obesity are limited to clinical studies and for some extraordinary medical situations. Gastric surgery also has been performed with successful results in adults, but there have not been enough studies in children to recommend this procedure.
Figure reprinted with permission from the American Journal of Clinical Nutrition.
Barlow SE, Dietz WH. Obesity evaluation and treatment: expert committee recommendations. Pediatrics 1998;102:E29.
Himes JH, Dietz WH. Guidelines for overweight in adolescent preventive services: recommendations from an expert committee. Am J Clin Nutr 1994;59:307-16.
Strauss R. Childhood obesity. Curr Probl Pediatr 1999;29:5-29.
Troiana R, Flegal KM, Kuczmarski RJ, Campbell SM, Johnson CL. Overweight prevalence and trends for children and adolescents. The National Health and Nutrition Examination Surveys 1963-1991. Arch Pediatr Adolesc Med 1995;149:1085-91.
About the Author
Dr. Travers is an assistant professor of pediatrics at the University of Colorado Health Sciences Center in Denver, Colorado. She is board certified in both pediatrics and pediatric endocrinology.
As a clinician at The Children's Hospital of Denver, she provides care to those children with various endocrine disorders. Her clinical and research interests include Turner syndrome and childhood obesity.
Copyright 2012 Sharon H. Travers, M.D., All Rights Reserved
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