New research from Denmark challenges traditional assumptions about weight and health, showing that being overweight or even moderately obese may not shorten life expectancy.
The large-scale study, presented at the European Association for the Study of Diabetes (EASD) Annual Meeting 2024 in Vienna, suggests that people with a BMI between 25 and 35 were no more likely to die within five years than those at the upper end of the so-called healthy range.
Underweight and lower-normal BMI linked to higher mortality
The analysis of more than 85,000 individuals revealed a surprising pattern. Those classified as underweight (BMI below 18.5) were almost three times more likely to die during the study period than those with a BMI between 22.5 and 25.
Even those in the lower half of the normal range (18.5 to 22.5) faced higher risks of death, despite technically being considered healthy.
Researchers caution that unintentional weight loss due to undiagnosed illness may partly explain this association, but the finding still highlights the risks of being too lean.
Overweight and moderate obesity show no extra risk
Individuals with a BMI between 25 and 30 (overweight) did not have a greater mortality risk. Those with a BMI of 30 to 35 (moderate obesity) also had no higher risk than the reference group.
This supports the concept of being fat but fit. In this concept, people with higher BMIs, yet without major metabolic complications, can remain relatively healthy.
By contrast, individuals with severe obesity (BMI of 40 or above) faced a risk of mortality. They were more than twice as likely to die as the reference group.
Fat distribution may matter more than BMI alone
The researchers stress that BMI is not a perfect measure of health. Two people with the same BMI can have very different risk profiles depending on where fat is stored.
Visceral fat is located deep inside the abdomen around vital organs. It has stronger links to type 2 diabetes and high blood pressure. It is also connected to cardiovascular disease.
By comparison, fat stored on the hips and thighs appears less harmful, highlighting the need for more personalized approaches to obesity treatment.
Possible explanations for the surprising findings
Lead researcher Dr Sigrid Bjerge Gribsholt notes that reverse causation may play a role. Individuals with undiagnosed illness might lose weight. This makes low BMI look riskier than it is.
Professor Jens Meldgaard Bruun, co-author of the study, adds that medical advances over recent decades may have changed the BMI range. This range is associated with the lowest mortality and may have shifted slightly upward.
Key takeaway: focus on health beyond BMI
While obesity remains a global health challenge, this study suggests that moderate excess weight may not automatically shorten life. Instead, factors such as fat distribution and fitness levels could be crucial. The presence of chronic conditions might also be more important indicators of long-term health.
As Professor Bruun concludes, “The treatment of obesity should be personalized. Factors like fat distribution and metabolic health matter as much as, or more than, BMI itself.”
