BMI of 27 equals obesity in over-40s

3 minute read

A study comparing the WHO definitions with one based on body fat has found many people with obesity are being missed. 

A stricter BMI cutoff for obesity should apply to people over 40 to reflect changing body composition, according to research presented at the European Congress on Obesity in Venice.  

It comes as the latest update from the Global Burden of Disease study, published in the Lancet, finds a 50% increase since 2000 in the number of healthy life-years lost due to metabolism-related risk factors.  

At the ECO this week, Italian and Lebanese researchers presented a cross-sectional study, published in Nutrients, involving 4800 adults whom they classified according to BMI cutoffs and then by body-fat measurements.  

Under WHO guidelines, a BMI of 18.5-24.99kg/m2 is normal, 25-29.99 is overweight and over 30 is obese.  

According to these cutoffs, 1087 participants (23%) were in the normal weight range, 1826 were overweight (38%) and 1887 had obesity (39%).  

They then had their total body fat percentage (BF%) measured with dual x-ray absorptiometry scans and were reclassified using a system that takes age and sex into account in defining obesity: in people aged 40-59, it’s a BF% of 40 or higher for females and 28 or higher for males; in people aged 60-79, it’s a BF% of 42 or higher for females and 30 or higher for males.  

According to this measure, about two-thirds of the group (71% of men and 64% of women) were obese. This corresponds to about 40% of women and about half of men with obesity being missed with BMI categorisation alone.  

For BMI to match the body fat classification system, the researchers said, the obesity cutoff for middle-aged people should come down to 27kg/m2.  

“This new BMI cut off recognises the physiological differences between middle-aged and older adults and younger populations,” said co-author Professor Marwan El Ghoch from the University of Modena and Reggio Emilia in Italy.  

“It’s likely that the changes in body composition across the lifespan, which seem to occur without a meaningful change in body weight, lead to higher adiposity at a lower BMI.” 

Co-author Professor Antonino De Lorenzo, from the University of Rome Tor Vergata, said the WHO standard missed “many middle-aged and older adults who are at risk for obesity-related diseases including type 2 diabetes, heart disease, and some cancers. Establishing this new BMI cut-off point in clinical settings and obesity guidelines will be beneficial to the potential health of millions of older adults.” 

The latest from the Global Burden of Diseases, Injuries, and Risk Factors Study found a 49% increase in DALYs between 2000 and 2021 due to high systolic blood pressure, high fasting plasma glucose, high BMI, high LDL cholesterol and kidney dysfunction.   

It found ill health among 15-49-year-olds was increasingly attributable to high body mass and high blood sugar.  

“With increasing exposure to risk factors such as high blood sugar, high blood pressure, low physical activity, and diet high in sugar-sweetened beverages, there is an urgent need for interventions focused on obesity and metabolic syndromes,” said Dr Greg Roth, Adjunct Associate Professor of Health Metrics Sciences at the Institute for Health Metrics and Evaluation, which coordinates the long-running study. 

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