According to British researchers the body/mass ratio (BMR)*, a measurement that is central to practically all medical research in which the patient’s weight is considered to be a factor, may not be as accurate a predictor of future morbidity in patients aged 75 and older as once thought
Instead of the BMI the study used the ratio of the circumference of the waist and of the hips to evaluate its value in predicting future morbidity and mortality in the elderly.
“Guidelines for optimal weight in older persons are limited by uncertainty about the ideal BMI or the usefulness of alternative … [measures]” writes lead researcher Gill M. Price, MD. “The usefulness of waist circumference (WC) or the Waist/Hip Ratio (WHR) as a predictor of mortality in older persons is also not established.”
In the study, which appears in the August issue of the American Journal of Clinical Nutrition, 14,833 volunteers aged 75 years or older were recruited in the United Kingdom. A complete baseline health assessment included measurement of BMI and waist and hip circumferences.
After a median follow-up period of 5.9 years the study found that there had been 6,649 deaths (46% due to circulatory diseases). Surprisingly, both the BMI and waist circumference were not accurate predictors of future morbidity and mortality. However an elevated WHR, or an increasing WHR as compared to baseline measurements, was found to correlate with death from circulatory conditions in both men (WHR > 0.99) and women (WHR > 0.90).
Although the researchers were quick to point out that there findings would require additional study and verification by other investigators, they did state that “current guidelines for BMI-based risk categories overestimate risks due to excess weight in persons aged Ã¢Â?Â¥75 years… Increased mortality risk is more clearly indicated for relative abdominal obesity as measured by high WHR.”
The Index Medicus citation for this study is Am J Clin Nutr. 2006; 118:669-682. An abstract (brief summary) can be read online at this link.
* The Body Mass Index (BMI) was derived by Belgian statistician, Adolphe Quetelet, who came up with the Quetelet Index of Obesity, which measured obesity by dividing a person’s weight (in kilograms) by the square of his or her height (in inches). In mathematical form,
BMI = W / H^2
According to the most recent guidelines the following are the “definitions” of a person’s weight based on their BMI:
Ã¢Â?Â¢ Underweight = <18.5
Ã¢Â?Â¢ Normal weight = 18.5-24.9
Ã¢Â?Â¢ Overweight = 25-29.9
Ã¢Â?Â¢ Obesity = BMI of 30 or greater
Current understanding of the BMI mandates the inclusion of the following caveats:
1) The BMI may overestimate the amount of body fat in athletes and those with muscular builds.
2) The BMI may underestimate the amount of body fat present in the elderly or those who have lost muscle mass.
The National Institutes of Health’s National Heart, Lung, and Blood Institute jointly publish information related to the BMI and its relationship to obesity. Their web pages are certainly worth taking a look at if you want more information on these, and other, body weight-related issues.
Much has been written recently about measuring “body fat content” or “body fat percentage” or some other “fat” term. A Google search using either term will probably return a few hundred thousand “hits.” Unfortunately, an overwhelming majority of those hits will be from web sites that have but one goal: to sell you whatever they can convince you that you need.
I ran a full Medline search (the database that lists every paper published in medical journals from around the world) and was unable to locate a single source stating that measuring the “body fat whatever” was superior to the BMI.
Keep that in mind if you are considering a purchase from one of the “online experts.”
The information presented in this article and its included links is of an informational nature only and is not intended as a recommendation of any changes in the reader’s health care program. Before making any changes in diet, medications, or other treatments the reader is strongly advised to consult with their health care provider.