Your Waistline Can Tell You a Lot About Your Health Risk

Summarized by Robert W. Griffith, MD
May 7, 2004

Introduction

Everyone knows their BMI¹, don't they? (If you don't, you can go to the first link below, which takes you to a BMI calculator). And everyone knows that a high BMI is a probable indicator of cardiovascular trouble to come (not to mention diabetes, knee osteoarthritis, an increased risk of cancer, and so on).

You can usually tell if you're overweight by just measuring your waist circumference (WC). So how good is a tape measure in predicting your health risk - as good as, or better than if you calculate BMI scores? Some Canadian doctors wanted to find out, and they've published their results in the American Journal of Nutrition.

What was done

The researchers used survey information gathered by the Center for Disease Control and Prevention (CDC) in Atlanta, USA, as part of their NHANES III study. Waist measurements and BMIs were available for almost 15,000 participants over 17 years of age.

Blood pressure, blood lipid profile, and fasting blood glucose were used to determine the risks for high blood pressure (hypertension), high cholesterol, and the metabolic syndrome. (To learn about the metabolic syndrome, also known as Syndrome X, go to the second link below).

The BMI and WC scores were used to allocate the subjects to different groups:

* 102 cm = 40 inches, 88 cm = 34½ inches

Test	Measurement	Group
BMI calculator	18.5 - 24.9	Normal
BMI calculator	25.0 - 29.9	Overweight
BMI calculator	30.0 - 34.9	Obese
Waist Circumference	men below 102 cm, women below 88 cm*	Normal
Waist Circumference	men over 102 cm, women over 88 cm	Increased

Because all those who were underweight (BMI below 18.5) had normal WC values, and all those with severe obesity (BMI over 35) also had increased WCs, they were left out of the full analyses.

What are known as Odds Ratios (ORs) were calculated for the different groups given above. An OR expresses the likelihood that a member of the group will develop the health risk, compared to a 'normal' subject.

As expected, the ORs were higher for overweight and obese subjects than for normal-weight subjects. Broken down according to the WC category (normal or increased WC), the results were similar.

These findings point to the waist circumference as being a significant predictor of increased health risk.

So, calculate BMI or measure girth?

The results of this analysis suggest that waist circumference is a better marker of health risk than BMI, and that greater emphasis should be paid to girth in classifying obesity. This might seem obvious to a layperson, but so much importance has been attached to the need to calculate BMI scores by health professionals in recent years that a reminder may be necessary.

Get out your tape measure and see just where your waist stacks up (or sags). And then draw the necessary conclusions - eat right, exercise, and get a check-up to see if you have any other indicators of increased cardiovascular or other health risks. Your tape measure may indeed be more useful than a BMI calculator.

Source

• Waist circumference and not body mass index explains obesity-related health risk. J. Janssen, PT. Katzmarzyk, R. Ross, Am J Clin Nutr, 2004, vol. 79, pp. 379--384

Footnotes
1. BMI stands for Body Mass Index, which is calculated based on your height and weight, and expressed in kg/m2. It gives a good idea of whether you are over- or underweight. A BMI of 18.5 to 25 is normal, from 25 to 30 indicates overweight, from 30 to 40 obesity, and over 40 severe or dangerous obesity.

Related Links
Tool: What's Your BMI
Tool: Do You Have the Metabolic Syndrome?
Obesity Increases Risk for Death from Cancer

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.