BMI or Body Mass Index-Ask Dr. Paul Library

DEAR DR. PAUL: What is BMI and is it used in children?

DR.PAUL ANSWERS: Very good question as the rate of overweight and obese children and adolescents has doubled over the last 2 decades. Medical complications of obesity usually seen only in adults, have now begun to appear in children and adolescents. Diabetes and cholesterol problems have reached almost epidemic proportions among children in North America. According to recent studies, 15.3% of 6-11 year olds and 15.5% of 12-19 year olds are considered to be overweight.

What is BMI? The Body Mass Index or BMI is used to assess the weight status of individuals. The BMI (the weight over the square of the height) is one of the best ways to indirectly measure total body fat. In adults, the weight status based on the BMI is as follows:

BMI less than 18.5 = Underweight
BMI 18.5 - 24.9 = Normal
BMI 25 - 29 = Overweight
BMI over 30 = Obese

In children, the BMI values vary with the age and sex of the child. The BMI in children is called: BMI-for-age. The BMI value itself, is plotted on a specific BMI chart. Just like the height and weight growth charts parents are familiar with, the BMI charts also contain a series of lines, which indicate specific percentiles. For example, if a 10-year-old boy's BMI is 18, this places him at the 75th percentile. This means that compared to other kids his age, 75% have a lower BMI than him. In children, instead of looking at the actual BMI value itself, we focus on the specific percentile of the BMI according to age and gender. BMI Percentiles indicate the following:

BMI-for-age less than the 5th percentile means underweight

BMI-for-age 85th to 95th percentile means the child is at risk for overweight

BMI-for-age greater than 95th percentile means the child is overweight

Why is the BMI-for-age important? Recent studies have shown that cardiac disease risk factors are associated with the BMI for age. 60% of children aged 5-10 years with a BMI-for-age greater than the 95%, had at least one obesity-related condition such as high blood pressure, high cholesterol, or high insulin levels (an indication type 2 diabetes). 20% of these children had 2 or more such abnormalities. According to The American Academy of Pediatrics, BMI for age is now the recommended method for screening overweight and underweight status in all children from 2 to 20 years of age.

As a result of the alarming increase in the number of overweight children and adolescents, physicians are now going to be looking at BMI as well as eating and physical activity habits more closely as part of the regular pediatric check up. The experience with adults shows very little success in terms of getting overweight adults to lose weight. Therefore prevention, especially in children, is the best approach. This requires the cooperation of the parents, physician, school and other societal/community members.

To download BMI-for-age charts click here.

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