Moving Beyond BMI

From the American Heart Association Waist Size, Exercise Keys to Health

CHICAGO—With all the talk about body mass index (BMI) these days, one could conclude that not having an optimal BMI might automatically translate into increased risk for diabetes and other chronic diseases. But has all the focus on BMI caused us to overlook other important disease indicators related to weight?

Barry Franklin, MD, addressed this question at the recent American Heart Association annual meeting, during a discussion of the obesity epidemic and the relationship between indices of obesity and chronic diseases. “Is it about weight, or waist, as we age?” Dr Franklin asked.

The Super-Sized Caskets Epidemic

“Let’s start with the obesity epidemic. What are the key things you need to know? I think an important point is that we really do have an obesity epidemic,” noted Dr Franklin, director of cardiac rehabilitation at William Beaumont Hospital, Royal Oak, Mich. This epidemic of obesity has been escalating over the past 20 years, he continued, to the point where new industries have emerged to meet the needs of this segment of the population. As examples he cited “reinforced office furniture, larger umbrellas, lifts in hospitals for patients. And this doesn’t stop just with the living. We have super-sized caskets today—a real testament to the current obesity epidemic that we have in the United States and in many countries.”

Dr Franklin pointed out that an estimated two thirds of all Americans are now classified as overweight or obese. “And perhaps equally disturbing is the fact that between 1996 and 2000, those with BMIs greater than 30, 40, and 50 doubled, quadrupled, and quintupled in the United States. Furthermore, we now recognize that this obesity epidemic is fueling the diabetes epidemic, and it’s estimated that by the year 2030, the number of people with diabetes will more than double.”

The Missing Link in Chronic Disease

Dr Franklin stressed that “obesity is truly the only central risk factor associated with a cascade of physiologic abnormalities, all of which accelerate the atherosclerotic process and lead to coronary heart disease, heart failure, and related sequelae.”

Diabetes Care

Ann Intern Med.

N Engl J Med

In his opinion, BMI provides a crude index of total adiposity or obesity, pointing out that many clinical studies have had similar results showing that high BMI is a risk factor for the development of type 2 diabetes in men and women (. 1994; 17:961-969; 1995; 122:481-486), and it increases the likelihood of death from cardiovascular disease, especially in men (. 1999; 341:1097-1105).

Lancet

An ongoing controversy, however, has been highlighted by a recent meta-analysis of 40 studies that included more than 250,000 patients with established coronary disease (. 2006; 368:666-677). The authors concluded that BMI fails as a cardiovascular risk factor. “The outcomes for total and cardiovascular mortality were actually better for overweight and mildly obese groups compared with normal-BMI patients,” Dr Franklin said.

How could this be? The 3 potential reasons discussed in the study were:

1. Overweight patients may have had better outcomes, because they had more muscle compared with normal-weight patients

2. Normal-weight groups in the studies generally had a lower prevalence of risk factors, and were thus less likely to receive effective secondary prevention interventions

3. The fact that BMI cannot discriminate between visceral fat and lean body mass.

“We now recognize certainly that body fat distribution is an important predictor of the health risks of obesity, and that those individuals with a preponderance of abdominal fat have a higher risk of developing hypertension, type 2 diabetes, dyslipidemia, coronary disease, and premature death as compared with individuals whose obesity is predominantly in the hip and thigh regions,” said Dr Franklin.

“Indeed, increasingly those of us who study these types of phenomena have come to the realization that we really need to better quantitate obesity and its distribution. And in fact, increasing data suggest important cut points: men with a waist circumference greater than 40 inches and women greater than 35 inches,” he continued.

Start Exercising Now

Evidence over the past 10 years has increasingly demonstrated the important role that exercise plays in cardioprotection, Dr Franklin noted.

Int J Obes Relat Metab Disord

One study (. 1995;19[suppl4]:S41-S44) involving more than 25,000 men with varied body compositions and fitness levels highlighted 3 major findings:

1. Overweight men have higher mortality rates than normal-weight men

2. Fit men (ie, those who exercise regularly) have comparable mortality, regardless of BMI

3. Unfit, normal-weight men are nearly 3 times as likely to die at a young age compared with their overweight counterparts who exercise regularly.

“They conclude in this study that although physical activity or exercise training may not make all people lean, it appears an active way of life may have important health benefits,” said Dr Franklin.

JAMA

Another study (. 1999;282: 1547-1553) took things one step further and produced “startling results,” he added. “If you look at normal-weight, overweight, and obese individuals, comparing fit versus unfit, basically what you see is that unfit individuals were nearly 3 to 5 times more likely to die than their fit cohorts. In fact, the impact was even greater between fit versus unfit and smokers versus nonsmokers for the same body weight cohorts.”

Dr Franklin concluded by stressing these 3 main points:

1. Environmental influences provide the most likely explanation for the current obesity epidemic

2. Chronic disease health risks are associated with obesity, which may be expressed as BMI, waist circumferences, waist-to-hip ratio, or a combination thereof

3. Aerobic fitness is an important modulator, regardless of body composition; it is inversely related to mortality and decreases the risk for death in normal-weight, overweight, and obese individuals.