New research presented at the European Association for the Study of Diabetes Annual Meeting 2025 suggests that people who are underweight or at the lower end of a “healthy” body mass index (BMI) face greater risks regarding life expectancy than those who are overweight or mildly obese.
The study included over 80,000 people in Denmark and followed them for five years. The participants had their BMI measured and were divided into four weight groups: underweight, healthy weight, overweight, and obesity. BMI is a measure of the ratio of one’s weight to one’s height squared, and it can be used to roughly measure whether a person is within a healthy weight range for their height. While BMI is not an accurate predictor of health or body fat for many individuals (especially athletes), it can be used at the population level to determine trends related to body weight and health. Increased BMI has been associated with many negative health outcomes, including increased risk of heart disease, type 2 diabetes, and certain cancers. The goal of this study was to see whether BMI categories are associated with lifespan in the general population.
The results showed that people in the overweight BMI category, and even some at the lower end of the obesity BMI category, were no more likely to die during the five-year follow-up period than people in the mid- to upper range of the healthy weight category. However, people in the underweight BMI category as well as those in the lower part of the healthy range had a greater chance of dying during the follow-up period. Specifically, people in the underweight category were nearly three times more likely to die than those in the upper part of the healthy weight range.
The authors noted that both being underweight and having obesity are global health issues that must be addressed. While the reason for the findings of this study are not known, it is possible that the ideal healthy weight is shifting slightly upward thanks to improvements in general health and medicine. Since this study was observational, it is also possible that the results were skewed by individuals who lot significant amounts of weight due to a medical condition. More research is needed to determine optimal BMIs, and individual needs may vary.
Sources: EASD 2025, Science Daily