new Obesity Definition Could Considerably Increase prevalence, Research Shows
A proposed redefinition of obesity, moving beyond reliance on body Mass Index (BMI), could dramatically increase the number of adults classified as having the condition in the United States, according to a new study published in JAMA Network Open. Currently, obesity is primarily defined by a BMI of 30 or higher. The proposed definition expands this to include individuals with a BMI over 40, those with a high BMI and at least one elevated measure of body fat (waist circumference, waist-to-hip ratio, or waist-to-height ratio), those with two or more elevated body fat measures nonetheless of BMI, or those with direct measurements of excess body fat via scans.
The proposed changes also suggest categorizing obesity into “clinical” (with signs of illness) and “pre-clinical” stages. Researchers, led by Dr. Lindsay Fourman of Mass General Brigham, applied both the traditional and new definitions to data from 301,026 participants aged 18-80 enrolled in a US health study between May 2017 and September 2023.
The results revealed a ample shift in prevalence. While 43% (128,992 participants) were classified as obese under the traditional BMI criteria, the new definition identified 69% (206,361 participants) as obese - a nearly 60% increase. This rise was particularly pronounced in older adults, with 78% of those aged 70 and over meeting the new criteria.
Crucially, the increase wasn’t simply a reclassification of the same individuals. 78,047 participants who would not have been considered obese based on BMI alone were identified as such under the new definition. Researchers emphasize that these individuals demonstrate a heightened risk of organ dysfunction and long-term health complications, justifying their classification. Nearly half (48%) of those identified as obese without a high BMI were found to have clinical obesity, while 56% of those obese based on BMI and other measures also fell into the clinical category.
The study also noted differences across demographics. While prevalence under the new definition was similar between men and women, men experienced a larger percentage increase. the relative increase in prevalence was greatest among Asian individuals, though the percentage point increase was comparable across racial groups.
Professor Naveed Sattar of the University of Glasgow, who was not involved in the research, called the findings ”thought-provoking” and highlighted the need for further investigation. He also noted that the new definition has not yet been officially adopted. Sattar underscored the broader issue, stating that current obesity levels, regardless of definition, present important challenges, particularly in high-income countries, and necessitate more effective strategies for promoting healthier lifestyles.
