BMI And Waist Circumference Risk Assessment
Chester J. Zelasko, Ph.D. | March 29, 2005

Think about this: you have a friend who is very overweight. You just know that he’s going to have a heart attack if he tries to climb a flight of stairs. Then your other friend, who doesn’t look overweight and seems to be in good shape, keels over with a heart attack. It doesn’t make any sense, does it? But it happens every day. It doesn’t mean that excess body weight is not a factor in the development of disease--it most assuredly is--but assessing the risk for developing a disease is complicated. This is especially true when it comes to non-invasive measures, including anthropometric measurements such as body weight. But recent research has developed a more precise way of assessing such risk, and that’s the topic of this Newsletter.

The Body Mass Index (BMI) uses height and weight to calculate the surface area of a human being: the more surface area you have, the more body fat you have, with the exception of those who are very muscular--professional football players, for instance. (Click here to determine your BMI.) BMI can tell you whether you’re normal weight, overweight, or obese. What it cannot do is predict whether you’re at greater or lesser risk for heart disease or diabetes because there are other factors to consider. One of those factors is visceral adiposity or the fat around your waist.

Researchers have discovered that the Waist Circumference (WC) is a much better predictor for determining who is at risk for heart disease and diabetes than BMI (1). If you have a tendency to store fat around your waist, the risk for heart disease and diabetes increases.

The measurement is simple. Using a flexible tape (a measuring tape is included with every 30 Day Plan), measure your waist at the widest point, usually an inch above or below the umbilicus (belly button). It should just cover your skin without making indentations. Don’t suck your gut in and hold your breath! Just stand normally. Measure three times and take the average.

You’re at increased risk for diabetes and heart disease if you are:
  • A woman with a waist circumference over 35 inches.
  • A man with a waist circumference over 40 inches.
While the WC has contributed more precision to the risk assessment than BMI alone, we know that heart disease and diabetes occur in people who have smaller waists than those cited above. This is especially true for people with a BMI less than 30 (normal weight or overweight, but not obese). There’s the possibility that increased fat around the waist, even though it did not reach the WC threshold, would still put those people at additional risk for heart disease.

As a result, researchers recently decided to address that problem (2). They combined anthropometric data from the NHANES III and the Canadian Heart Health Study. Their goal was to increase the sensitivity and specificity of the WC over all ranges of BMIs. Just like the WC threshold for men and women, they wanted to determine if there are more specific WC thresholds for people who were normal weight and less overweight. They used the Framingham coronary heart disease risk index as the criteria for heart disease risk.

They found that indeed, there are varying WC measures that put people at higher risk for heart disease even though they may not be overweight; the table they developed is replicated below. It increases the specificity of the BMI, especially for those whose BMI is in the Normal Weight and Overweight categories. If your waist exceeds the threshold within a given category, you are at a greater risk for heart disease, regardless of your BMI.

BMI Category
Normal Weight Overweight Obese I Obese II and III
BMI (kg/m2) 18.5 to 24.9 25 to 29.9 30 to 34.9 >35
Waist (inches)
Men 35.5 39.0 43.0 49.0
Women 31.5 35.5 41.5 45.0

If you find that your WC at your BMI category is more than it should be, make an appointment with your physician and develop a plan for addressing the issue. Remember--these simple measurements are an initial step. Your physician can do additional testing of blood pressure and serum lipids to make a more precise analysis of your health risk.

Your health is in your hands--don’t drop the ball! Better Life is here to help you with the 30 Day Plan and the Walking book to get your risk under control once again.

References:
  1. Wilson, P and Grundy, S. The Metabolic Syndrome Practical Guide to Origins and Treatment: Part I. Circulation. 2003;108:1422-1425.

  2. Ardern, Chris I., Ian Janssen, Robert Ross, and Peter T. Katzmarzyk. Development of health-related waist circumference thresholds within BMI categories. Obes Res. 2004;12:1094 –1103.
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