However, a new study to be presented at the European Congress on Obesity in Malaga calls the relevance of this tool into question.
Conducted by researchers from the University of Rome “Tor Vergata,” the University of Modena and Reggio Emilia in Italy, and the Beirut University in Lebanon, under the direction of Professor Marwan El Ghoch, this study sheds new light on the evolution of obesity with age.
The main takeaway is that it’s not so much BMI that changes over the years, but rather the distribution of fat and muscle tissue.
To reach these conclusions, the researchers studied the body composition of 2,844 adults with a BMI of at least 25.
Body mass index is calculated by dividing a person’s weight (in kilogrammes) by their height squared (in metres). Currently, a person is considered obese with a BMI equal to or greater than 30.
In order to analyse the evolution of the distribution of fat and muscle mass, the participants were classified into three age groups: young adults (20-39 years old), middle-aged adults (40-59 years old) and seniors (60-79 years old).
They were compared with each other after being matched by body weight and BMI.
The results reveal that, over the years, fat mass increases while muscle mass decreases, particularly in men.
In women, these variations are more subtle, but a trend emerges: with age, abdominal fat increases (from +1.23% to +4.21%), while muscle mass in the limbs decreases (from -0.81 kg to -2.63 kg). However, the BMI hardly changes at all.
This paradox reveals a major flaw in that BMI does not measure the true evolution of the body, nor to identify the associated risks.
“These results clearly indicate that we cannot rely only on BMI without considering the content and distribution of body composition in people with obesity across the different age groups,” Professor El Ghoch explains in a news release.
A crucial issue in the face of rising obesity worldwide
The specialist emphasises the importance of analysing the distribution of body mass, as an excessive accumulation of abdominal fat combined with muscle wasting can have serious health consequences.
This tissue transformation promotes chronic low-grade inflammation, increases insulin resistance and increases the risk of cardiometabolic diseases, regardless of BMI.
This study reopens the debate on the reliability of BMI. Its authors call for a paradigm shift in the assessment of obesity and suggest the use of more accurate indicators, such as waist-to-height ratio or muscle strength tests.
“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 [middle-aged and older people],” the researcher explains.
However, longitudinal studies will be necessary to confirm these observations and refine the tools for measuring obesity across the ages.
These issues are becoming increasingly important with the emergence of a new class of drugs, “GLP-1 agoists,” which include semaglutide (Ozempic, Wegovy) and liraglutide (Saxenda).
Composed of compounds that mimic digestive hormones, these treatments act on satiety and are revolutionising the treatment of obesity. But their real effectiveness could be better evaluated with more reliable indicators than BMI.
The stakes are high: without significant political intervention, nearly 60% of adults and one-third of children and adolescents worldwide could be overweight or obese by 2050, according to projections published in March in the British medical journal, The Lancet.
There is therefore an urgent need to use more precise tools that are capable of reflecting the biological reality of the human body. The future of public health may depend on it.