More Than Meets the Scale

Why a Weigh-In Isn't Enough to Identify Obesity and Its Health Risks

Sep 2, 2009

Women struggle with weight loss goals that depend on pounds lost. However, the amount and location of fat may be more reflective of health than the number on the scale.

Body mass index (BMI) and weight circumference (WC) are two easy, at-home measurements that describe the proportion of fat in the body and its location. Together, they help predict abnormal weight status and obesity-related health risks.

What is BMI?

BMI is a number that indirectly differentiates between weight from fat alone (and not from muscle) and total weight, on the basis of a person's height and overall weight and a standard expected proportion of fat to muscle in the body. The equation's result is charted onto a weight status graph. Although BMI is considered extremely accurate, there are variances in its accuracy for different ethnic groups; nonobsese, muscular athletes (increased BMI); and women (who tend to have more fat than BMI suggets compared with men).

What is WC?

Because no single number of weight or fat alone can tell the entire picture, the National Heart, Lung, and Blood Institute includes waist circumference as a second measurement of obesity and weight-related health risks. Excess fat is stored by the body either under the skin (as with the thighs) or around internal organs (as with the liver and other abdominal locations). The simple WC measurement around the waistline quickly reveals if body fat has collected in the abdominal area.

How to Measure BMI and WC

The BMI calculation needs an accurate height and weight. Charted BMIs are categorized as normal, underweight, overweight, or obese; adults are charted separately from children. You can enter these numbers into the Centers for Disease Control and Prevention BMI tool, or you can calculate your own BMI with this formula:

Use a tape measure to determine WC by measuring from hip bone to hip bone at the navel, all the way around your body. According to an April 7, 2008 NIH news release about results of the Nurses Study in Circulation online, this measure is as reflective of abdominal fat as the waist-to-hip circumference ratio, but it is easier to obtain accurately. The goal WC for adults is 25 inches or less; WC greater than 35 in women indicates higher risk of disease.

Risks Associated With Increased BMI and WC

BMI and WC combination charts describe risk levels regardless of obesity status. According to these charts, adults with increased WC and BMI have very high risks of disease, even if the BMI is not at the obese level. Increased BMI alone indicates increased disease risk, and increased WC alone indicates high risk of disease.

New evidence from the study in Circulation online identifies women in particular as having an increased risk of death from cancer and heart disease in proportion to increased WC, even when BMI indicates normal weight. An increasing risk was present with increasing BMI, however, so obesity leads to increased risk of disease as well.

Considerations for Weight Loss

Although the risks and statistics sound dire, careful measurement of BMI and WC, rather than pounds alone, is a positive step toward improved lifestyle changes and health goals. Because these numbers reflect ratios, not absolute numbers, small changes can have large impacts to decrease health risks quickly. So, forget those last 5 pounds and work toward reducing BMI and WC by a few numbers instead.

References

Weight-Control Information Network: Weight and Waist Measurement Tool for Adults

The copyright of the article More Than Meets the Scale in Weight Loss is owned by Nicole Van Hoey. Permission to republish More Than Meets the Scale in print or online must be granted by the author in writing.