Are BMI Cutoffs Missing Millions of the World's Obese?

Body mass index has long been known to be an imperfect instrument; it can declare world class athletes obese while missing people with high body fat on a slender frame.

The body mass index, or BMI, has become the worldwide standard for finding people who are obese or at risk of obesity. But it’s long been known to be a less than perfect measure.

Based only on height and weight, BMI can categorize muscular persons—even world-class athletes—as obese, while missing those with unhealthy levels of body fat on slender frames.

Now, a study from Arizona State University, published in Obesity Reviews, suggests that this latter problem, which would miss millions of people with high body fat in East Asian countries, may mean we’ve undercounted the world’s obese population by at least 400 million. If conquering obesity means targeting at-risk children, this means some groups might be missed completely, the authors find.

“A century of work in human biological variation suggests that human populations can vary dramatically in underlying body form in a way that may require population-sensitive cutoffs for monitoring,” they write. They outline an alternate set of methods for evaluating populations’ excess energy reserves, introducing the idea of “basal slenderness.” In short, what is the expected BMI before a population is exposed to urbanization, high-calorie Western diets, and other influences?

Making BMI adjustments specific to a population would do more to truly estimate how many are overweight or underweight—and allow world public health agencies to better target their efforts.

Similarly, a 2015 study in Diabetes Care, the official journal of the American Diabetes Association, said recommended BMI levels for Asians should be lower for due to known physical differences.

Using alternate measures, the authors believe the true population of obese worldwide may be 400 to 500 million higher than the World Health Organization’s current estimate of 600 million, which is based on those who have a BMI of 30 or more. The WHO estimates that 1.9 million are overweight, which is based on those who have a BMI of 25 or more.

Reference

Hruschka DJ, Hadley C. How much do universal anthropometric standards bias the global monitoring of obesity and undernutrition? [published online July 6, 2016] Obes Reviews. 2016; doi: 10.1111/obr.12449.