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I think I'm healthy but my BMI says I'm overweight Add to ...

Question: How much credence do you put in the BMI measurement? I think I’m healthy but my BMI says I’m overweight.

Answer: If you’re between the ages of 18 and 65, BMI (body mass index) is a height and weight formula that gives a pretty reliable snapshot of your body fat. The easiest way to determine your BMI is to use an online calculator (google BMI calculator). It’s determined by dividing your weight (in kilograms) by your height (in metres squared).

Health professionals and researchers use BMI to classify body weight and assess a person’s risk for disease. BMI values from 18.5 to 24.9 are defined as healthy or normal weight and linked with a lower risk of health problems.

As your BMI goes up, so does your risk for type 2 diabetes, heart disease, high blood pressure, gallbladder disease, sleep apnea and some types of cancer. If your BMI falls between 25 and 29.9 you’re classified as overweight; a BMI of 30 or greater is considered obese.

BMI values less than 18.5 are considered underweight and increase a person’s risk for conditions such as osteoporosis, nutrient deficiencies and eating disorders.

That said, the BMI has a few drawbacks. For starters, it doesn’t tell you where you’re carrying your body fat, which is important in determining obesity-related health risk. Excess fat around the abdomen is associated with greater health risk than fat located on the hips and thighs.

It also doesn’t distinguish between body fat weight and muscle weight. Athletes and heavily muscled people may have a high BMI but very little fat (Given an equal volume, muscle weighs more than fat on the scale).

To prevent being misclassified based on BMI, some people prefer to have their body fat measured at the gym or their doctor’s office.

If you want to know where your fat is located, and how that fat is affecting your health, you need to measure your waist.

That’s because waist circumference is a good measure of visceral fat, the type of deep fat that packs itself around the organs and secretes chemicals that increase the body’s resistance to insulin and cause inflammation throughout the body.

A waist circumference of 94 cm (37 inches) or greater for men and 80 cm (31.5 inches) or greater for women increases the likelihood of type 2 diabetes, high blood pressure, elevated cholesterol, heart attack, stroke, metabolic syndrome and some cancers.

In fact, studies have shown that increased girth predicts a person’s risk of disease and death better than BMI alone.

I think you need to know both your BMI and your waist circumference because both are important predictors of health.

Send dietitian Leslie Beck your questions at dietitian@globeandmail.com. She will answer select questions, which could appear in The Globe and Mail and/or on the Globe website. Your name will not be published if your question is chosen.

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The content provided in The Globe and Mail's Ask a Health Expert centre is for information purposes only and is neither intended to be relied upon nor to be a substitute for professional medical advice, diagnosis or treatment.

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