Understanding the BMI Scale and Where You Fit In

A person's body mass index (BMI) is their weight in kilograms divided by the square of their height in meters. A high BMI can indicate high body fatness, which puts you at risk for many diseases.

BMI doesn't measure body fat directly, but it correlates moderately with more direct measures of body fat. In addition, it is strongly correlated with various metabolic and disease outcomes, which are more direct measures of body fatness.

At Advanced Surgical Associates of Northern Minnesota, Dr. John Bollins and his staff perform weight loss surgery, for which BMI is one of the significant factors in determining if a patient is a good candidate. Knowing your BMI is also essential when considering what lifestyle changes are appropriate for eating more healthily and exercising more regularly, improving your overall health. Here's how it works.

What does BMI show?

For adults 20 or older, the BMI is interpreted using standard weight status categories. These categories are identical for men and women of all body types and ages.

When using these categories, BMI can be interpreted as follows:

BMI: Below 18.5

Weight status: Underweight

BMI: 18.5 – 24.9

Weight status: Healthy weight

BMI: 25.0 – 29.9

Weight status: Overweight

BMI: 30.0 and above

Weight status: Obesity

Because standard categories are used, even if two people have the same BMI, their level of body fat may differ.

In general:

• At the same BMI, women have more body fat than men
• At the same BMI, the amount of body fat may be higher or lower depending on the person’s racial/ethnic group
• At the same BMI, older people tend to have more body fat than younger adults
• At the same BMI, athletes generally have less body fat (and more muscle mass) than non-athletes

The accuracy of BMI for indicating body fatness also appears to be higher in people with both higher BMI and body fatness levels. While a person with a very high BMI (e.g., 35 kg/m2) most likely has high body fat, a relatively high BMI may also be due to high lean body mass (muscle and bone), such as in an athlete. The need for such knowledge is why you should have a trained healthcare provider perform health assessments to evaluate an individual's health status and risks.

While BMI in children is calculated using the same formula as for adults, the results are interpreted differently. Children's and teens' BMI must be age- and sex-specific because the amount of body fat differs between girls and boys and changes with age. The CDC's BMI-for-age growth charts consider these differences and visually show BMI as a percentile ranking determined using representative data of the US population of two- to 19-year-olds collected in surveys from 1963-65 to 1988-94. Obesity is defined as being at or above the 95th percentile of children the same age and sex as those in the reference population.

The takeaway

BMI is among many factors that determine the healthy weight of individuals and populations, and as a general tool, it works well. For example, knowing your BMI can indicate whether you should diet or if a medically supervised weight loss program would be better for you.

Do you have questions? Want to know more about how your BMI affects your life? Contact Advanced Surgical Associates of Northern Minnesota by calling our office in Hibbing, Duluth, or Ely, Minnesota, or booking your appointment online.

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