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 BMI, he and his associates looked at several body habitus measures in 7,634 healthy volunteers who participated in the third National Health and Nutrition Examination Survey (NHANES III).
All of the subjects were at least 18 years of age. Overall, 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-to-hip ratio, and waist-to-thigh ratio.
The research team analyzed the contribution of these measures to insulin resistance and diabetes mellitus, two important factors underlying cardiovascular disease. The measures were analyzed according to gender.
The investigators found significant correlations between all the body measures and both insulin resistance and diabetes mellitus, 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 diabetes mellitus (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.
Surprisingly, the study indicated that cardiovascular risk profiles actually improved for some people with a BMI over 35 kg/m
“If we are operating on the basis of BMI, we are operating on the wrong people,” he commented.
“I operate on a large number of patients, and I'm surprised at the small number of cardiovascular complications I see. You would expect to see more cardiovascular disease in the population we treat,” Dr. Livingston noted. “One reason people get really huge is an unlimited ability to store subcutaneous fat from the food they take in. It may not mean they have an elevated cardiovascular risk.”
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 BMI is not direct, Dr. Livingston said.
The results of the study suggest that body habitus measurements should be incorporated into routine screening of candidates for bariatric surgery, Dr. Livingston explained.