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Dear Diabetes: What’s My BMI?

Understanding and calculating body mass index

Have you ever wondered about the terms “underweight,” “normal weight,” “overweight” and “obese”? What do these categories mean and how accurate are they?

Their history goes back to the 19th century, when a Belgian mathematician, Lambert Adolphe Jacques Quetelet, invented what he believed was a way to help understand “normal” weight relative to height in an adult human. Originally referred to as the Quetelet index, Quetelet’s formula was renamed the body mass index, or BMI, by American scientist Ancel Keys in his 1972 study of the health risks of obesity.

Formula to calculate BMI

While BMI is not the most accurate measure of body fat, it may be useful for adults 20 years and older as a quick and easy way of determining the general ballpark of a person’s relative weight category, such as the difference between being overweight and obese. Weight is an important risk factor for conditions including type 2 diabetes.

How is BMI calculated?

BMI is determined by first dividing a person’s weight (in pounds) by their height squared (in inches), and then multiplying the result by 703. So, for a person 148 pounds and 5 feet 7 inches (67 inches) tall, their BMI = (148 ÷ 672) x 703, or 23.2. (Multiply 67 by 67 to get 4,489, then divide 148 by 4,489 to get 0.03296948, and finally, multiply that last number by 703, which will give you 23.1775451, or 23.2).

If using the metric system, calculate BMI by dividing a person’s weight in kilograms by their height in centimeters squared, and then multiplying the result by 10,000 (BMI = [weight(kg) ÷ height(cm)2] x 10,000). For a person weighing 67 kilograms who is 170 centimeters tall, multiply 170 by 170 to get 28,900, then divide 67 by 28,900 to get 0.00231834. Multiply that by 10,000, which will result in 23.1833910, and round down to 23, which is their BMI.

But there’s a much easier way; use an online BMI calculator. Enter your weight and height and the calculator will give you your BMI.

Understanding BMI results

A BMI of:

18.5 or less may be considered underweight
18.5 to 24.9 may be considered normal or healthy weight
25 to 29.9 may be considered overweight
30 or more may be considered obese

However, these are not hard-and-fast categories, especially for individuals whose body build may have more than average muscle mass.

For many adults 20 years and older, these categories may provide a general target weight range, although other factors, including age, gender and health, should also be considered. Be sure to talk to your diabetes care team before making any changes to your diabetes management routine, or if you have questions about your diabetes goals.

What if my BMI is higher than normal?

According to one study, higher BMI is directly related to a person’s chances of developing diabetes, especially in younger adults. People with a BMI over 30 (“obese”) whose fat is concentrated around the waist are also at higher risk for hypertension (high blood pressure) and cardiovascular disease.

Aiming for and maintaining a target BMI may play a role in one’s overall diabetes management strategy. Any weight loss goals should be made in consultation with a physician or appropriate Certified Diabetes Educator® (CDE*), who can help put a plan in place and develop strategies for following a meal plan, being mindful of portion sizes, keeping physically active and reducing sedentary time.

*“Certified Diabetes Educator” and “CDE” are certification marks owned and registered by the National Certification Board for Diabetes Educators (NCBDE). NCBDE is not affiliated in any way with Sanofi US. NCBDE does not sponsor or endorse any diabetes-related products or services.

© 2016 The DX: The Diabetes Experience

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