CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Sheldon E. Litwin, MD, FACC*
* University of Utah Hospital, Cardiology, 30 North, 1900 East, 4A100 SOM, Salt Lake City, Utah 84132 (Email: sheldon.litwin{at}hsc.utah.edu).
Drs. Green and Lesser each raise several legitimate and thought-provoking issues regarding the article by Gelber et al. (1) and my accompanying editorial (2). Their letters highlight several of the more important challenges that we face in confronting the obesity epidemic—first and foremost among these is the very problem of defining obesity. I concur that there is no single measure of adiposity that is simple to obtain, highly reproducible, widely available, and fully reflective of cardiovascular (or other) risk. Given this problem, I tried to make a case in the editorial that for a majority of the population, particularly those in the age range where interventions intended to induce loss of fat are most likely to be beneficial (younger and middle-age patients), body mass index (BMI) performs nearly as well as waist circumference (or waist/hip or waist/height). Therefore, until we find a better measure of fatness, I opined that we should continue to use BMI. All that being said, I readily agree that BMI has significant limitations as a means to define and quantify obesity.
Dr. Green correctly points out the irresolvable problem of relating population statistics to the care of individual patients. While I agree fully with this point, I believe that the dilemma is equally applicable to the use of either BMI or waist circumference as a measure of adiposity and the risk of developing cardiovascular disease. The fact is that not all patients "at risk" develop disease, and not all disease occurs in patients with a known predisposing risk factor. Regardless of how much we argue about the relative merits of different risk stratification schemes, at the end of the day, we are still left with considerable uncertainty in the treatment of individuals.
The condition of "normal weight obesity" characterized by muscle wasting and abdominal obesity has recently received a lot of press. Although this condition certainly exists, it is largely a problem of elderly patients. In the elderly population, age itself will almost certainly be a more potent risk marker than abdominal obesity. Weight loss in this population may not be of much benefit in terms of reducing cardiovascular end points. In the middle-age population where application of preventive principles is more likely to be cost effective, normal weight obesity is uncommon and the use of a simple metric like BMI will identify the majority of patients at risk of obesity-related complications. Even though BMI is an imperfect measure of fatness (particularly visceral fat), it is also likely that waist circumference will not be a reliable measure of visceral fat volume in all patients. Drs. Green and Lesser both point out that as clinicians and scientists, we wish to have information about both lean and fat body mass in our patients. I agree with this sentiment and thank Dr. Lesser for highlighting the large effect of lean body mass on BMI calculations. Unfortunately, it is difficult or impossible to obtain measures that accurately separate muscle and fat mass in the typical clinical setting.
Interestingly, most obesity researchers have used a single cutoff for abnormal waist circumferences (102 cm in men and 98 cm in women) regardless of height or other measures of overall body size. It is obvious to all of us that most biological processes do not behave as dichotomous variables, but rather as continuous variables with varying degrees of abnormality. As such, I suggest that if we are to adopt metrics of abdominal obesity based on waist circumference, that we use a graded system (i.e., mild, moderate, or severe) that somehow takes into account body frame size (e.g., normalizing waist to height).
I thank both authors for their letters. I very much welcome and encourage open debate and discussion about the topic of obesity. This extraordinarily important issue that will inevitably consume increasing amounts of our time and health care dollars.
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References
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1. Gelber RP, Gaziano JM, Orav EJ, Manson JE, Buring JE, Kurth T. Measures of obesity and cardiovascular risk among men and women J Am Coll Cardiol 2008;52:605-615.[Abstract/Free Full Text]2. Litwin SE. Which measures of obesity best predict cardiovascular risk? J Am Coll Cardiol 2008;52:616-619.[Free Full Text]
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