Beyond BMI: Scientists Say Body Weight May Not Reveal the Full Picture of Obesity - Video

Is BMI alone enough to determine whether someone has obesity? A new study suggests that traditional body mass index measurements may not accurately reflect the health risks associated with excess body fat, while a newer classification system could provide a clearer picture of obesity-related health problems.

Published in the International Journal of Obesity, the study conducted by researchers from University College London and collaborating institutions examined how a new clinical obesity classification compares with conventional BMI categories.

Researchers analysed health data from 6,978 adults aged 46 years who participated in the 1970 British Cohort Study. The traditional BMI system classifies individuals as overweight when their BMI is between 25 and 29.9 and as having obesity when their BMI is 30 or higher. However, the newer system considers excess body fat, organ dysfunction, and limitations in everyday physical activities.

Under this approach, people with excess body fat but no related health problems are classified as having preclinical obesity, while those experiencing obesity-related organ dysfunction or functional limitations are classified as having clinical obesity.

The findings revealed that 52.5% of participants had preclinical obesity, while 17.7% had clinical obesity. Another 29.8% were classified as having no obesity. In comparison, the conventional BMI system classified 32.4% of participants as having obesity and 37.8% as overweight. Importantly, among participants classified as having obesity based on BMI, only 31.4% met the criteria for clinical obesity under the new system. The remaining participants were classified as having preclinical obesity.

Researchers also found that 16.6% of individuals in the BMI-defined overweight category met the criteria for clinical obesity. Clinical obesity was associated with higher odds of death compared with having no obesity, while BMI-defined obesity showed no statistically significant association with mortality.

However, researchers cautioned that the small number of deaths limited the strength of these findings. Further research is needed to determine whether the newer classification can reliably predict long-term health risks across different populations.

REFERENCE: Blodgett JM, Mitchell JJ, Makaronidis J, Hamer M (2026). International Journal of Obesity. DOI: 10.1038/s41366-026-02257-2, https://www.nature.com/articles/s41366-026-02257-2