Twice as many US adults have obesity based on assessment of their fat volume by DEXA scan compared with measurement of body mass index (BMI), a finding that highlights the shortcomings of BMI and adds to the growing case that BMI alone should not be the default gauge for obesity.
"BMI vastly underestimates true obesity," Aayush Visaria, MD, said at ENDO 2023: The Endocrine Society Annual Meeting.
His findings highlight that "BMI should be supplemented with other measures of obesity" for the management of individual patients, with assessments that could include a bioelectrical impedance scale or waist circumference, said Visaria, who is a researcher at Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey.
Visaria cited a new policy issued by the American Medical Association a couple of days before his presentation, as reported by Medscape Medical News, which advises that BMI "be used in conjunction with other valid measures of risk such as, but not limited to, measurements of visceral fat, body adiposity index, body composition, relative fat mass, waist circumference, and genetic/metabolic factors."
The study by Visaria and colleagues used data from 9784 US adults ages 20-59 years (average age, 39 years) collected in several National Health and Nutrition Examination Surveys in 2011-2018. All these participants underwent DEXA assessment of their total body fat as well as a BMI calculation.
Using standard obesity cutoffs for both BMI and total body fat, Visaria found that DEXA rated 74% of participants as having obesity based on body fat compared with 36% based on BMI.
Among the 64% of the study group who were not obese by BMI, DEXA scans showed 53% of this subgroup did have obesity based on body fat content. Among those with a normal BMI, 43% had obesity by DEXA result.
Further analysis showed that when Visaria added waist circumference to BMI to enlarge the diagnostic net for obesity it cut the percentage of adults missed as having obesity by BMI alone nearly in half.
Additional analyses showed that the rate of missed diagnoses of obesity by BMI was only most common among people of Hispanic or Asian ethnicity, with both groups showing a 49% rate of obesity by DEXA among those with normal-range BMIs.
The rate of missed obesity diagnoses was highest among all women, with a 59% prevalence of obesity by DEXA among women with a normal-range BMI.
Basically, this study measured almost 10,000 Americans BMI and bodyfat percentage. Obesity was defined as bodyfat percentage of 25% or more in men (unsure of the percentage for women). Almost 3/4 of participants were found to have obese levels of bodyfat, even though only around 1/3 had obese BMI.
I thought this study was kinda funny because BMI is often criticized by weightlifters for failing to account for increased levels of muscle, with the implication that it overestimates obesity. You often hear this from bloofy permabulkers, eg “I’m not obese, muscle weighs more than fat!” Turns out, it’s the opposite … bmi UNDERestimates obesity
The other, more concerning, number is that 3/4 study participants had obese levels of bodyfat. Three out of four! Insanely fucked
