Overweight, obesity protective against death?

A large study from Denmark presented at EASD 2025 suggests that overweight and obesity may protect against death.

“We found a U-shaped association between BMI and mortality, with the lowest mortality associated with a BMI between 22.5 and 30 kg/m²,” said the researchers.

Compared with the reference cohort (BMI 22.5 to <25 kg/m²), the risk of death was highest at the far ends of the BMI spectrum – the underweight (BMI <18.5 kg/m²; adjusted hazard ratio [aHR], 2.73), lower healthy weight (BMI 18.5 to <20 kg/m²; aHR, 2.00), and severe obesity (BMI ≥40 kg/m²; aHR, 2.10) groups.

The risk was not as high in the middle healthy weight (BMI 20 to <22.5 kg/m²; aHR, 1.27) and obese (BMI 35 to <40 kg/m²; aHR, 1.23) ranges. [EASD 2025, abstract 327]

Conversely, mortality risk was similar between the reference population and those in the overweight range (aHRs, 0.95 and 0.96 for BMI 25 to <27.5 and 27.5 to <30 kg/m², respectively) and those in the lower end of the obese spectrum (BMI 30 to <35 kg/m²; aHR, 1.05).

“We found no large differences according to sex, comorbidity level, and educational level,” said the investigators.

Why the U-shaped association?

“There are conflicting findings about the BMI range linked to the lowest mortality. It was once thought to be 20 to 25 [kg/m²], but it may be shifting upward over time owing to medical advances and improvements in general health,” noted study lead investigator Dr Sigrid Bjerge Gribsholt from the Aarhus University Hospital in Denmark, in a press release.

The team used data on BMI from a large cohort of Danish individuals who had undergone DXA scans (n=97,848). About 9 percent (n=7,808) of the participants died during follow-up.

“One possible reason for the results is reverse causation – some people may lose weight because of an underlying illness. In those cases, it is the illness, not the low weight itself, that increases the risk of death, which can make it look like having a higher BMI is protective,” said Gribsholt. “Since our data came from people who were having scans for health reasons, we cannot completely rule this out.”

“It is also possible that people with higher BMI who live longer (most participants were elderly) may have certain protective traits that influence the results. Still, in line with earlier research, we found that people in the underweight range face a much higher risk of death,” she added.

Fat distribution also matters

Hence, BMI is not the only indicator for unhealthy levels of fat, noted study co-investigator Professor Jens Meldgaard Bruun, also from the same institute. “Other important factors include [fat distribution].”

Visceral fat, for instance, though stored deep within the abdomen, is metabolically active and secretes compounds that adversely affect metabolic health. As such, an individual who has a BMI of 35 kg/m² and visceral fat may have type 2 diabetes (T2D) or high blood pressure, Bruun explained.

In contrast, an individual with the same BMI but with excess fat distributed on the hips, buttocks, and thighs may be free of such comorbid conditions, he continued.

“It is clear that the treatment of obesity should be personalized to take into account factors such as fat distribution and the presence of [comorbidities] when setting a target weight,” Bruun added.