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HEALTH & WELLNESS

BMI might not tell the whole truth

The measurement of weight health can often be imprecise or wrong, experts say.

April 17, 2011|Melissa Healy

But researchers are increasingly looking for ways to capture such information with tools as simple and inexpensive as tape measures.

One of the easiest alternatives to the BMI is waist measurement. With growing evidence that fat girdling the waist and visceral organs disturbs metabolism, the circumference of a patient's midsection has been shown to be a better predictor of Type 2 diabetes risk. Several large studies have linked a waist circumference greater than 40 inches for men and 35 inches for women to a higher risk of cardiovascular disease and Type 2 diabetes, as well as earlier mortality -- with every inch beyond those thresholds adding risk.

For The Record
Los Angeles Times Wednesday, April 20, 2011 Home Edition Main News Part A Page 4 News Desk 1 inches; 59 words Type of Material: Correction
Body mass index: An April 17 article in Section A on the limitations of the body mass index (BMI) said the BMI was calculated by dividing a person's weight by his height, squared. That formula applies to measurements in kilograms and meters. When calculating BMI using inches and pounds, the result of the formula should be multiplied by 703.
For The Record
Los Angeles Times Sunday, April 24, 2011 Home Edition Main News Part A Page 4 News Desk 1 inches; 59 words Type of Material: Correction
Body Mass Index: An April 17 article in Section A on the limitations of the body mass index (BMI) said the BMI was calculated by dividing a person's weight by his height, squared. That formula applies to measurements in kilograms and meters. When calculating BMI using inches and pounds, the result of the formula should be multiplied by 703.

A twist on that approach, described last month in the journal Obesity, is a measure of hip circumference. When combined with a person's height, the "body adiposity index," proposed by Bergman at USC, offers a simple gauge of how much of a person's body is made up of fat, and what its proportion is to muscle, bone and water.

Finally, an increasing number of researchers cite a major gap in the BMI: its inability to reflect the health effects of a person's exercise habits. At least seven high-profile studies in the last decade have established that even for people with high BMIs, cardiovascular risk and the likelihood of early death are driven down significantly by maintaining a high level of fitness or at least regular physical activity. The risk of Type 2 diabetes also falls, although in that case, studies suggest that whittling waist circumference is a better strategy.

The bottom line: "It's important not only to look at the weight status of a patient, but other factors such as physical activity" in assessing his or her health prospects, said Dr. Amy Weinstein, an internal medicine physician at Harvard University's teaching hospital, Beth Israel Deaconess Medical Center.

Even as they gain more and better tools to assess their patients' health prospects, physicians will -- and should -- continue to use the BMI as well, Weinstein said. It gives a rough approximation of a person's fat, which clearly plays a role in promoting certain diseases. And for busy doctors, she added, the BMI is easy, familiar and cheap.

--

melissa.healy@latimes.com

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