Childhood Obesity:

September 1, 2004

ABSTRACT: To assess a child for overweight, begin by calculating his or her body mass index (BMI). Note that BMI is used differently in children than it is in adults. A child's BMI is plotted on a growth curve that reflects that child's age and gender. This yields a value-BMI-for-age-that provides a consistent measure across age groups. Children whose BMI-for-age is between 85% and 95% are at risk for becoming overweight. Any child whose BMI-for-age is 95% or more is considered overweight. The 2 main factors associated with overweight in children are poor eating habits and decreased physical activity. Recommend that children have at least 5 servings of fruits and vegetables a day. Children should engage in moderate physical activity for at least 60 minutes on most days of the week, and TV viewing and computer activities should be limited to no more than 2 hours a day.

Childhood obesity is rapidly becoming a public health problem in the United States. Approximately 15% of Americans aged 6 to 19 years-more than 9 million children and adolescents-are overweight.1 The percentage of African American and Hispanic children who are overweight is even higher than that seen in the nation as a whole.2

Which children are at risk for obesity-and how best to intervene? Here we discuss how to calculate body mass index (BMI) in children and identify those who require further evaluation. We also outline practical steps to help prevent and treat childhood obesity.


Overweight children are at increased risk for the development of major health problems, including:

Insulin resistance and type 2 diabetes mellitus.

Hepatic disease.



Sleep apnea.

Pseudotumor cerebri.

Orthopedic complications.

Overweight children and adolescents can also experience mental health problems, such as low self-esteem, loneliness, depression, and nervousness.3 These feelings can lead to other behaviors associated with poor health, such as smoking, alcohol consumption, and increased overeating.

The probability that overweight children will become overweight adults is 50%. For adolescents, the probability increases to between 70% and 80%.2


The number of overweight children has risen dramatically over the past 3 decades (Figure). National Health and Nutrition Examination Survey (NHANES) data from 1971 to 1974 show that 4% of children aged 6 to 11 years were overweight; nearly 30 years later, the percentage has almost quadrupled to 15%.4 Data for 12- to 19-year-olds show that the percentage has tripled since 1980, from 5% to 15%.4 Among minority populations, the increase in childhood obesity is even greater.

Because the rate of childhood obesity has increased so quickly in recent years, changes in the behavior of children are most likely a major cause. Although genetics and endocrine conditions may contribute to the increasing rate, the role of such factors is small. The 2 main risk factors associated with overweight in children are:

Decreased physical activity.

Poor eating habits.

Basically, overweight is a problem of energy balance-expenditure of calories versus intake of calories.

Decreased physical activity. Data from the third NHANES survey show that 20% of children aged 8 to 16 years are involved in 2 or fewer sessions of physical activity per week.5 Sedentary behaviors such as watching TV, playing on the computer, and playing video games often replace physical activity.

A reduction in the time devoted to physical education and a decline in the number of children who walk to school have also contributed to the problem.6 According to the National Association for Sport and Physical Education, the majority of US high schools require students to take only 1 year of physical education in order to graduate.7

Poor eating habits. In the past 2 decades, significant changes have occurred in the composition of a typical child's diet and in the manner in which children eat. For example, compared with 20 years ago, children consume a greater number of calories each day and fat constitutes a larger percentage of their dietary intake. Numerous factors have contributed to these changes, including alterations in family meal patterns and an increase in food choices and availability.2 Most meals are eaten outside the home, which generally results in larger portion sizes and consumption of foods that are higher in fat.2 Families who eat meals together usually eat more vegetables and less saturated fat and fried food.2


How to use BMI in children. One of the first steps in the assessment of a child for overweight is to calculate his or her BMI. This measurement is used in adults and children to identify obesity, to gauge the degree of body fat, and to help predict the risk of secondary complications.8

BMI can be calculated using either kilograms and meters or pounds and inches. The original formula for determining the BMI of an adult is the person's weight in kilograms divided by the square of the height in meters.9

BMI = weight in kilograms ÷ (height in meters)2

BMI can also be calculated by dividing the person's weight in pounds by the square of the height in inches, then multiplying the result by 703.9

BMI = [(weight in pounds) ÷ (height in inches)2] × 703

Adults are categorized as follows based on their BMI:

Underweight: below 18.5.

Normal: 18.5 to 24.9.

Overweight: 25.0 to 29.9.

Obese: 30.0 and above.

In children, however, BMI is used differently. Because children's body fat varies with age and gender, a child's BMI is plotted on a growth curve that reflects that child's age and gender. This plotting yields a value-BMI-for-age-that provides a consistent measure across age groups. As with other growth curves, percentile scores indicate how a particular child compares with other children of the same age and gender. Note that BMI-for-age should be used only as a screening tool for the assessment of overweight in children; it is not recommended in children younger than 2 years.

In 2000, the CDC released updated growth charts for children aged 2 to 20 years that allow clinicians to plot a child's BMI and determine his BMI-for-age. These charts are available online at growthcharts.

Four classifications are used in the interpretation of BMI-for-age: underweight, healthy, at risk for overweight, and overweight. The Table lists cut-off points for each category.

Children whose BMI-for-age is 5% or below are considered underweight and require a thorough health assessment to determine the cause. Children whose BMI-for-age falls between 6% and 85% are generally considered to be at a healthy weight.

Those children whose BMI-for-age falls between 85% and 95% are at risk for becoming overweight. Any child whose BMI-for-age is 95% or above is considered overweight (as defined by BMI alone).

Be sure to use accurate weight and height measurements when calculating BMI-for-age. A small error in measurement can result in a large discrepancy on the BMI-for-age growth chart. Also keep in mind that visual inspection alone (ie, "Does the child look overweight?") cannot substitute for an accurate measure of risk for overweight.

When further evaluation is warranted. An expert committee convened in 1994 by the Bureau of Maternal and Child Health at the Health Resources and Services Administration developed a chart to help clinicians provide a thorough assessment.10 If a child's BMI-for-age is between 85% and 95%, further screening is necessary (Algorithm). Assess the following parameters in children at risk for overweight10,11:

Family history. Ask about obesity, type 2 diabetes, eating disorders, heart disease, high blood pressure, and hyperlipidemia in family members.

Large change in BMI-for-age. This is most easily identified by monitoring a child's BMI-for-age over time; early intervention can prevent a child's becoming severely obese.

Concern about weight. Ask the child-or a family member-if he ever worries about weight gain.

Total cholesterol level.

Blood pressure.

If such an assessment reveals any risk factors, conduct an in-depth medical assessment.

Finally, a thorough evaluation is required for any child whose BMI-for-age is at or above the 95th percentile. In addition, consider interventions to maintain the current weight or, in some instances, to initiate weight loss.


Because children are still growing, weight loss is usually not recommended. First, strive to maintain a child's baseline weight; this will result in a gradual reduction in BMI as the child grows. Weight loss is recommended in children aged 2 to 7 years only if a secondary complication, such as hyperlipidemia or hypertension, exists.8 In this setting, you may want to consider a weight loss plan-with a goal of no more than a 1-lb loss per month.10

For children aged 7 years and older, consider weight loss if the child's BMI-for-age is 95% or greater, or if the child is at risk for overweight (BMI-for-age, 85% to 95%) and has secondary complications.8

Dietary modification. The Food Guide Pyramid, developed by the US Department of Agriculture (USDA), can be used to help teach children about a well-balanced diet. This guide is geared toward children older than 6 years. On its Web site (www.usda. gov/cnpp), the Center for Nutrition Policy and Promotion (a division of the USDA) illustrates types and quantities of foods and the degree to which various diets comply with recommendations in the Dietary Guidelines and the Food Guide Pyramid.

For children aged 6 years and younger, the USDA has developed the Food Guide Pyramid for Young Children. This is essentially the same food guide, but it uses smaller serving sizes. It is available at: cnpp/KidsPyra/LittlePyr.pdf.

Most children need to consume more fruits and vegetables. The current recommendation is 5 servings of fruits and vegetables a day (3 of vegetables and 2 of fruit). In addition, children should reduce their consumption of sugary drinks and replace them with more water. It may be helpful for parents and children to start slowly by adding 1 additional serving of fruit or vegetables per week, rather than making large changes quickly. The same strategy can be used with beverages by slowly replacing sodas and other sugary drinks with water.

A healthful breakfast is also important.12 Children who eat a well-balanced breakfast that includes low-fat, high-nutrient foods may be less likely to snack during the day.Examples of good choices might be cold or hot high-fiber cereal with low-fat milk, or fruit and whole wheat toast with peanut butter.

Sometimes parents use food in ways that are detrimental to a child's health. Try to help parents and caretakers identify these behaviors and understand the effect they have on children. Using food as a reward gives children the wrong message. Withholding food as a punishment also sends an unhealthy message, for it implies that food can be used as a bargaining tool. Also, experts do not recommend allowing children to eat snacks while watching TV, because many children may overeat or choose less healthy foods in this setting.

Physical activity. Ask overweight or at-risk patients and their families about the child's daily physical activity. Include in the assessment:

Time spent in moderately vigorous activity both in and out of school, such as organized sports or physical education classes.

Time spent in sedentary behaviors, such as watching TV, playing video games, or playing on the computer.

The US Surgeon General recommends that children engage in moderate physical activity for at least 60 minutes on most days of the week.12 Many children and parents may not understand what is meant by moderate activity, especially if the parents do not exercise. In general, moderate physical activity should make a person sweat. Because it may be difficult to engage a child in a single activity for an hour, it is important to reassure parents that the 60 minutes can be broken up into smaller time segments, such as 10-minute intervals.

Encouraging children to decrease the amount of time they spend in sedentary behaviors, such as watching TV or playing on the computer, will help free time for more physical activity. Experts recommend that children limit "screen time" to no more than 2 hours per day.6

Family involvement can also have a positive effect on a child's level of activity. Discuss with parents the importance of serving as role models for both good nutrition and physical activity. Children find it easier to make changes in their behavior if the rest of the family is participating in the changes as well.12

Finally,as with dietary modification, setting small initial goals will keep children from becoming discouraged and will give them a sense of accomplishment.


Like adults, children do not eat a healthy diet or participate in physical activity for a wide variety of reasons. Discuss these barriers as part of your assessment of an overweight or at-risk child, and take them into consideration when planning treatment.

Environment. Sometimes a child's physical environment can help promote sedentary behavior. Children who live in unsafe neighborhoods are often confined to their homes and left with TV and video games for entertainment. Encourage these children and their families to find alternative activities that can be engaged in within the home, or explore with them ways to make activity outside safer, such as a parent walking a child to school.

Socioeconomic status. Recommend food substitutions that are both inexpensive and low in fat and calories. For example, frozen fruits and vegetables-in most instances-provide adequate nutrients but cost less than their fresh counterparts. Also, suggest physical activities that do not require expensive equipment, such as racing, dancing, jumping, and playing tag.

Schedule. Children who are home alone after school tend to spend more time engaged in sedentary activities while eating foods high in fat and sugar. Children whose parents work in the evening must choose their dinner themselves; their selections also tend to be foods high in fat and calories.6

Encourage families to eat as many meals together as possible and to make selections for nutritious snacks and meals ahead of time. Giving children healthy choices still allows them to feel in charge of their diet, but it limits unhealthy selections.

Age and gender. As girls reach adolescence, their physical activity levels start to decline.12 The Commonwealth Fund found that only 67% of high school girls engage in moderate exercise 3 or more times a week (compared with 80% of high school boys), while 15% of girls do little (once or twice a week) or no exercise.13 Encourage adolescent girls to find some type of activity, whether group or individual, that they enjoy and that will provide them with a moderate level of exercise.

Psychosocial issues. Children who eat excessively or when they are not hungry may be suffering from an eating disorder. Assess the child for depression if you note signs of hopelessness or sadness, sleep changes, or appetite changes.8 Eating may also be a way in which children respond to stress in their lives, since they are more limited than adults in the ways they can react to stress.14 n



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