If you've done your homework, you already know that measuring just your weight won't tell you how healthy you are; taller teens should naturally weigh more than shorter teens and athletic teens often weigh more than skinny, sedentary teens. Instead, assessing your body fat percentage will give you a better understanding of your overall fitness.
Normal Body Fat Gain
When child bodies transition into teen bodies, hormonal fluctuations cause fat and muscle ratios to go through normal changes. While guys may notice that their muscles grow faster than they once did, girls notice that they have developed additional body fat, particularly in the chest and waist. Because of these changes, and because not all teens develop at the same pace, a "normal" body fat percentage range is broader for teens than it is for children and adults.
Common Measures
Multiple methods can accurately assess body fat percentage. For example, a method called near-infrared interactance sends a beam of infrared light into the biceps, and a technique called dual energy X-ray absorptiometry (DXA) uses two types of X-ray to detect tissues and fats in the body. Another method, called skinfold estimation, involves pinching the skin with calipers on various points of the body to measure the thickness of subcutaneous fat layers.
Body Mass Index
According to the Centers for Disease Control and Prevention (CDC), Body Mass Index (BMI) is a technique that is generally a reliable indicator of body fatness for teens. It relies on a specific mathematical equation based on height and weight, but pre-set BMI calculators do most of the work if they are given two numbers to work with. Although BMI doesn't directly measure body fat, it is comparable to direct body fat measures such as the DXA.
Charting BMI
As with any body fat percentile measure for teens, BMI for teens is specific to age and sex (typically called BMI-for-age). As a result, BMI charts specifically gauge teens' BMIs based on percentile lines. For example, a teen in the 50th percentile ranks close to the group average for his sex and age, which generally puts him in a healthy range. Teens who are below the 5th percentile are considered underweight, teens between the 5th and under the 85th percentile are considered a healthy weight, teens between the 85th and under the 95th percentile are considered overweight, and teens equal or greater to the 95th percentile are considered obese. BMI can be an inaccurate representation of body fat percentile and health for some teens, though. For example, teens with higher than average muscle mass have a higher BMI, and small teens may still have more than a healthy amount of body fat.
Scheduling a Doctor's Visit
Concerned teens or parents of teens should seek guidance from a doctor who can help determine whether a body fat percentage is too high. A doctor can assess a teen's medical history and her family health history, and then compare them to physical activity levels and dietary habits. He can also offer advice on making healthy lifestyle choices and prescribe treatments for any underlying conditions.
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