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This page was reviewed or revised on Saturday, October 26, 2002.

Teen Weight Concerns

Teens want to know if their weight is normal. Girls often think they weigh too much and boys worry they are not big or strong enough. Teens must understand that the height, weight and body composition changes that occur during the teenage years will affect their weight. These changes, and the rate at which they occur, are greatly influenced by family traits.

Height

Nearly one quarter of final adult height results from the teenage height spurt. This spurt occurs between the ages of 10 and 13 years for most girls, and between 12 and 15 years for most boys. Since the height spurt occurs sooner in girls than in boys, some girls feel too tall, whereas boys are concerned by the delay in growth. Growth stops at around 16 years of age for girls and 18 years for boys.

Weight and Body Composition

Weight gained during the height spurt can account for 40% of the healthy adult weight. The weight gain differs in boys and girls. Girls put on more body fat during the teenage years than boys. Girls enter puberty with only 16% body fat and by adulthood reach 27%. Boys enter puberty with about 5% body fat, increase to 11% early in puberty, and maintain this level into adulthood.

Muscle mass peaks after the height spurt in both girls and boys. This increase is twice as great for boys than girls. Increase in muscle strength occurs after this increase in mass.

In boys, the height and weight spurts occur at the same time. In girls, the height spurt occurs before the weight spurt.

"Tempo"

A very important issue in the growth of teens is "tempo". This is the rate at which teens mature physically and sexually. For example, two boys may be the same height at 11 years old and again at 16 years old. Yet at 13 and 14 years of age, one may be 5 inches taller, weigh more, be nearly twice as strong and be more developed sexually than the other.

The timing of physical changes can have social and emotional effects. Boys who mature early tend to be taller, stronger, and better at team sports than boys who mature late. Even though they may not be more mature emotionally or intellectually, people may believe they are and therefore treat them differently.

Early maturation for girls may be a social drawback. They may need more reassurance about their early growth than girls who mature later.

These changes that occur during adolescence often cause teenagers to be preoccupied with self, concerned about what is normal, and they compare themselves with others.

Assessing Weight and Body Composition

The physical changes of adolescence and the variation with which they occur, make assessing the weight and body composition of teenagers hard.

Teens often want to know if their weight is normal. However, weight alone does not provide useful information. Weight, when considered in relation to height as Body Mass Index, is an indicator of body composition, or fatness.

Larger Body Mass Index values mean higher degrees of fatness.

The Body Mass Index (BMI) is calculated by:

For BMI to be useful for teens, standards must be defined by age, and sex, since fatness is known to vary with these factors. The following chart provides BMI ranges for most adolescents by age and sex:

A BMI within these ranges does not ensure a healthy weight. Further research in this age group is needed to accurately define when health is changed by high or low BMIs.

The ranges given may be useful, in letting teenagers of many shapes and sizes know that they fall within a range that describes most teens of their age and gender.

Body Mass Index values are more meaningful if information about the nutritional and physical activity habits of the teenager are also known. If the BMI is near the upper end of the range and nutritional and physical activity habits are poor, the teen is likely overweight. If the BMI is near the lower end of the range and nutrition habits are restrictive and/or physical activity habits are excessive, this can be a sign of problems that affect normal growth.

Only 5% of teenagers will have BMIs above and below these numbers. These teenagers should be referred for further medical assessment.