Definition of Obese

BMI in children and teens

There are several ways to find your BMI.

Doctors and nurses often use BMI to help find out if a person might have a weight problem. BMI gives a good estimate of total body fat for most people, but it doesn’t work well for everybody. For example, bodybuilders or other very muscular people can have a high BMI because of their muscle mass, even though they’re not necessarily overweight.

For most adults, the BMI is a good way to get an idea of healthy weight ranges. But it’s not always the final word in deciding if a person is overweight or obese. There are other things to think about when judging how much someone should weigh.

A person with a high BMI should be evaluated by a health care provider, who might use other factors such as skinfold thickness (a measure of body fat), waist size, evaluations of diet and family health problems, and other factors to find out if a person’s weight might pose a health risk.

BMI can be calculated the same way for children and teens as it is for adults, but the numbers don’t have the same meaning. This is because the normal amount of body fat changes with age in children and teens, and is different between boys and girls.

To account for this, the US Centers for Disease Control and Prevention (CDC) has developed age- and gender-specific growth charts. These charts are used to translate a BMI number into a percentile based on a child’s sex and age. The percentiles are then used to determine the different weight groups:

  • Underweight: less than the 5th percentile
  • Normal weight: 5th percentile to less than the 85th percentile
  • Overweight: 85th percentile to less than the 95th percentile
  • Obese: 95th percentile or higher

An easy way to determine your child’s BMI percentile is to use the CDC’s online BMI percentile calculator at http://apps.nccd.cdc.gov/dnpabmi.

Even in a young person, being overweight or obese can cause health problems. And it may directly increase the risk for certain health problems later in life, including some kinds of cancer. It also increases the chances of being overweight or obese as an adult, as well as the risk of health problems that can come with this.

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2Freedman, D.S., Horlick, M. {amp}amp; Berenson, G.S., 2013. A comparison of the Slaughter skinfold-thickness equations and BMI in predicting body fatness and cardiovascular disease risk factor levels in children. Am. J. Clin. Nutr., 98(6), pp.1417–24.

3Wohlfahrt-Veje, C. et al., 2014. Body fat throughout childhood in 2647 healthy Danish children: agreement of BMI, waist circumference, skinfolds with dual X-ray absorptiometry. Eur. J. Clin. Nutr., 68(6), pp.664–70.

4Steinberger, J. et al., 2005. Comparison of body fatness measurements by BMI and skinfolds vs dual energy X-ray absorptiometry and their relation to cardiovascular risk factors in adolescents. Int. J. Obes., 29(11), pp.1346–1352.

5Sun, Q. et al., 2010. Comparison of dual-energy x-ray absorptiometric and anthropometric measures of adiposity in relation to adiposity-related biologic factors. Am. J. Epidemiol., 172(12), pp.1442–1454.

6Lawlor, D.A. et al., 2010. Association between general and central adiposity in childhood, and change in these, with cardiovascular risk factors in adolescence: prospective cohort study. BMJ, 341, p.c6224.

7Flegal, K.M. {amp}amp; Graubard, B.I., 2009. Estimates of excess deaths associated with body mass index and other anthropometric variables. Am. J. Clin. Nutr., 89(4), pp.1213–1219.

8Freedman, D.S. et al., 2009. Relation of body mass index and skinfold thicknesses to cardiovascular disease risk factors in children: the Bogalusa Heart Study. Am. J. Clin. Nutr., 90(1), pp.210–216.

9Willett, K. et al., 2006. Comparison of bioelectrical impedance and BMI in predicting obesity-related medical conditions. Obes. (Silver Spring), 14(3), pp.480–490.

Boham E, Stone PM, DeBusk R. Obesity. In: Rakel RE, Rakel DP, eds. Textbook of Family Medicine. 9th ed. Philadelphia, PA: Elsevier; 2016:chap 36.

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Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults: a report of the American College of Cardiology/American Heart Association Task Force on practice guidelines and The Obesity Society. Circulation. 2014;129(25 Suppl 2):S102-S138. PMID: 24222017 www.ncbi.nlm.nih.gov/pubmed/24222017.

Adam Tsai, MD, of Kaiser Permanente Colorado and a spokesman for the Obesity Society, agrees. «The risks go up and up as BMI increases,» he says.

Obesity puts extra stress on your bones, joints, and organs, making them work harder than they should. Too much body fat raises your blood pressure and cholesterol, and makes heart disease and stroke more likely. It also worsens conditions like osteoarthritis, back pain, asthma, and sleep apnea.

Too much fat causes inflammation that can damage cells. Obesity is also linked to several types of cancers. It can also make your body respond less well to insulin, which controls your blood sugar. Over time, that can lead to type 2 diabetes.

The weight makes it harder to be active, too. «Carrying around extra pounds takes extra energy, so it can be difficult for obese people to exercise,» Tsai says.

If you think calories are the only thing that matters, think again.

No doubt: Calories definitely count. But so do a lot of other things, like whether you can afford healthy foods and can easily use parks, sidewalks, or other places where you can be active.

«For many people, it’s not an individual choice,» Wang says.

Your emotions, and how you handle them, also matter. Many people eat when they’re mad, sad, bored, or stressed. Weight problems can add to that. If you feel badly or are self-conscious about your body, that can hold you back from the full life that people of all sizes deserve. In turn, you eat more, seeking comfort.

Obesity can run in families, too. Your genes might be part of the reason. And you probably got your lifestyle and eating habits from your family, too. You can change those habits, though.

Your friends also count. Some research shows that obesity is «contagious» socially. In one study of some 12,000 people, Harvard researchers found that if someone gains weight, their family, friends, and partners also tend to gain weight, even if they don’t live near each other. Their influence affects you.

Also, you might’ve heard about studies that show links to air pollution, viruses, exposure to certain chemicals, or even the bacteria in a person’s gut. But they don’t prove that those things cause obesity.

«There’s a lot we still don’t know,» but it’s clearly not just about self-control, Wang says.

Calculating my BMI

You can also calculate your own BMI. The actual formula to determine BMI uses metric system measurements: weight in kilograms (kg) divided by height in meters, squared (m2).

When using pounds and inches, the formula needs to be altered slightly. Multiply your weight in pounds by 703. Divide that by your height in inches, squared:

BMI = (your weight in pounds x 703) ÷ (your height in inches x your height in inches)

For example, if you weigh 120 pounds and are 5 ft. 3 in. (63 in.) tall:

BMI = (120 x 703) ÷ (63 x 63) or 84,360 ÷ 3969 = 21.3

This is well within the healthy weight range.

Charts and online calculators

Charts and tables, such as the one below, are one easy way to figure out your BMI. There are also several online BMI calculators, such as this one on our website.

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