Body composition is a better predictor of health status and mortality risk than one’s body mass index (BMI), a measure of body fat based on height and weight, according to a new study in Annals of Internal Medicine.
The study, “Relationship Among Body Fat Percentage, Body Mass Index, and All-Cause Mortality,” published online March 8, may offer one explanation for the much debated “obesity paradox,” a theory that suggests body fat may actually provide some kind of protective benefit. Some studies have shown that people with moderate obesity, as measured by BMI, and chronic diseases are living longer than those with similar health conditions, but not considered to have obesity.
“BMI, which is essentially a measure of body weight, is not the whole picture when it comes to assessing somebody’s health,” said researcher William D. Leslie, MD, a professor of medicine and radiology at the University of Manitoba, Winnipeg, Canada. “Being underweight can be as harmful as being overweight. It’s really excess fat that contributes to mortality,” said Dr. Leslie in a video statement provided by the American College of Physicians (ACP).
In the observational study, researchers measured body fat using dual-energy x-ray absorptiometry (DXA) and collected BMIs in about 50,000 men and women. They found that having a higher percentage of body fat was independently associated with reduced survival, as was having a low BMI. Men and women with the greatest amounts of body fat were more likely to die over the next 4.5
to 6.7 years.
Men in the top 20 percent of those studied had at least 36 percent body fat and women had about 39 percent or higher. Men in this group were 59 percent more likely to die during the study period than men who had body fat in the 28 to 32 percent range. Women were 19 percent more likely to die than women in the 30 to 34 percent body fat range. At the same time, those considered “obese” by BMI standards alone, did not show an increased risk
The study authors say, that in some people, a higher BMI may mean more muscle, not fat. They conclude that their “findings may help explain the counterintuitive relationship between BMI and mortality.”
Private health insurers and Medicare continue to rely on BMI cutoffs first established in the 1991 National Institutes of Health (NIH) guidelines to determine eligibility for bariatric surgery. The guidelines recommended that bariatric surgery should be considered for patients with a BMI over 40, or over 35, if other major diseases are present.
In 2012, the ASMBS issued a position statement on bariatric surgery in Class 1 obesity (BMI 30 to 35) arguing that BMI thresholds were outdated. “The existing cut-off of BMI which excludes those with Class 1 obesity was established arbitrarily nearly 20 years ago. There is no current justification on grounds of evidence of clinical effectiveness, cost-effectiveness, ethics or equity that this group should be excluded from
“BMI is an important measure, but it’s not the only measure,” said Raul Rosenthal, MD, president of the American Society for Metabolic and Bariatric Surgery (ASMBS). “We need to look beyond BMI and not unnecessarily exclude a treatment because of this