Why your BMI might not tell the whole story about your health

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New research suggests that Body Mass Index (BMI), a widely used method to determine weight status, may not be the best tool for assessing obesity as people age.

The study, set to be presented at the European Congress on Obesity in Malaga, Spain in May, reveals that individuals with the same BMI can have significantly different body compositions, depending on their age.

Conducted by researchers from the University of Rome “Tor Vergata”, the University of Modena and Reggio Emilia in Italy, and Beirut University in Lebanon, the study found that older adults with obesity tend to have more fat stored in the torso area, and less muscle mass in their arms and legs, compared to young individuals with the same BMI.

The researchers analyzed data from more than 2,800 adults with a BMI of 25 or higher, categorizing them into three age groups: young adults (20 to 39 year old), middle-aged adults (40 to 59 years old), and older adults (60 to 79 years old).

Using an imaging technique, known as Dual-energy X-ray absorptiometry, they found that while BMI remained similar across all groups, fat distribution and muscle mass changed significantly with age.

This type of X-ray uses low-dose x-rays to measure bone mineral density (BMD) – which is the amount of mineral content in a given area of bone – and body composition, including total and regional body fat and lean tissue mass.

Marwan El Ghoch, one of the study’s authors, explained in a news release that BMI does not account for shifts in body fat and muscle mass over time, adding that middle-aged and older adults tend to store more fat in their abdomen while losing muscle in their limbs despite having the same BMI as younger individuals.

The study suggests redistribution of fat and muscle could increase the risk of health issues, such as chronic inflammation, insulin resistance, and heart diseases without changes to the BMI.

“Accordingly, the use of BMI becomes useless and misleading, and future research is needed to identify new tools that are able to detect these changes in fat and muscle mass in this specific population,” El Ghoch said.

The findings suggest that relying solely on BMI may ne misleading for diagnosing obesity and health-related risks. Instead, researchers recommend alternative measures, such as waist-to-height ratio and muscle strength assessments, like the handgrip test.

The study also emphasizes the need for future research to develop better tools for evaluating body composition in people with obesity.