ORLANDO — Body mass index alone is not a good indicator of cardiovascular risk in the morbidly obese and should be supplemented with body habitus measures for screening bariatric surgery candidates, Edward H. Livingston, M.D., said at the annual meeting of the American Society for Bariatric Surgery.
“We rely on BMI as the basis of all bariatric surgery criteria. BMI is thought to correlate to morbidity, but the relationship is not perfect,” said Dr. Livingston, professor of surgery at the University of Texas, Dallas.
In an effort to go beyond body mass index (BMI), he and his associates looked at several body habitus measures in 7,634 healthy volunteers who participated in the National Health and Nutrition Examination Survey III (NHANES III).
All subjects were at least age 18 years. The study population was 53% female, and the ethnic breakdown was 41% white, 28% black, 27% Hispanic, and 4% other.
The body habitus measures examined were subcutaneous skinfold thickness, waist circumference, waist/hip ratio, and waist/thigh ratio.
The team analyzed the contribution of these measures to insulin resistance (IR) and diabetes mellitus (DM), two important factors underlying cardiovascular disease.
The measures were analyzed according to gender.
The investigators found significant correlations between all the body measures and IR and DM, except for suprailiac skinfold thickness and development of diabetes in men, Dr. Livingston said.
Interestingly, thigh skinfold thickness was a strong negative predictor for the development of obesity and DM (0.31 odds ratio for diabetes among women and 0.38 among men), Dr. Livingston reported. This suggests that accumulation of fat in the lower body protects against insulin resistance and diabetes mellitus, he noted.
The study indicated that cardiovascular risk profiles actually improved for some people with a BMI over 35 kg/m
For example, triglycerides typically rise as a function of BMI but drop off after 35, Dr. Livingston said.
“If we are operating on the basis of BMI, we are operating on the wrong people,” he said.
“I operate on a large number of patients, and I'm surprised at the small number of cardiovascular complications I see,” Dr. Livingston continued.
“You would expect to see more cardiovascular disease in the population we treat,” he said.
“One reason people get really huge is an unlimited ability to store subcutaneous fat from the food they take in,” he said.
“It may not mean they have an elevated cardiovascular risk,” Dr. Livingston added.
In response to a meeting attendee's question, Dr. Livingston further explained that “the relationship of central obesity to cardiovascular risk factors has been overstated. A number of studies show cardiovascular disease is a function of total upper body fat and not visceral fat.”
The heterogenicity of body fat distribution among obese patients may explain the discrepancy in findings among different studies that have linked BMI to mortality, Dr. Livingston said.
Since 1991, the National Institutes of Health has recommended bariatric surgery for appropriate candidates with a body mass index of 40 or greater. The NIH consensus statement addressed concerns about increased mortality in this patient population.
Although cardiovascular disease is the leading cause of death in the morbidly obese, the relationship to body mass index is not direct, Dr. Livingston pointed out.
The results of the study suggest that body habitus measurements should be incorporated into the routine screening of candidates for bariatric surgery, he asserted.