Body Mass Index (BMI) has long been used to classify individuals as normal weight, overweight, or obese. Yet, new research will be presented at the European Congress on Obesity (ECO 2025, Malaga, Spain, May 11–14). It suggests BMI is an unreliable indicator of obesity-related health risks.
Scientists from the University of Rome “Tor Vergata,” the University of Modena and Reggio Emilia, and Beirut University found that people with obesity, despite having the same BMI, show major differences in fat and muscle distribution as they age. These findings challenge the effectiveness of BMI as the primary tool for assessing obesity.
Fat And Muscle Shift With Age
The study analyzed 2,844 adults with a BMI of 25 kg/m² or higher. Researchers used Dual-energy X-ray Absorptiometry (DXA) scans to measure fat and muscle composition. Participants were divided into three age groups:
- Young-age (20–39 years)
- Middle-age (40–59 years)
- Older-age (60–79 years)
Results showed that men experienced a steady increase in total body fat as they aged. They also experienced a decline in lean mass. In contrast, women maintained relatively stable levels of both.
However, both middle-aged and older adults, regardless of gender, had:
- Higher trunk fat (+1.23% to +4.21%)
- Lower appendicular lean mass (ALM) (–0.81 kg to –2.63 kg)
This means more fat around the abdomen and less muscle in arms and legs, despite no significant change in BMI.
WHY BMI FAILS AS A HEALTH MEASURE
Professor Marwan El Ghoch, University of Modena and Reggio Emilia, explains:
“Our study shows BMI does not reflect the real changes happening in body composition. Older adults with obesity tend to store more fat in the trunk. They lose muscle in their limbs. Yet, their BMI remains unchanged.”
This redistribution of fat and muscle has serious health risks, including:
- Chronic inflammation
- Insulin resistance
- Higher risk of cardiometabolic diseases
“Using BMI alone can be misleading. We need better tools to assess fat distribution and muscle loss, especially in older adults,” El Ghoch warns.
A NEW APPROACH TO MEASURING OBESITY
Instead of relying solely on BMI, researchers suggest using:
- Waist-to-height ratio, a better indicator of abdominal fat.
- Muscle mass and strength assessments, such as the handgrip test.
These methods provide a clearer picture of an individual’s health risks. The study calls for further longitudinal research to develop more accurate obesity assessment tools.
