Obesity is often considered one of the most important factors in the likelihood of early death, but a recent US review reveals that cardiorespiratory fitness actually has more of an influence on mortality risk and our long-term health.
In other words, while obesity is connected to many health issues, being fit is more important than being thin when it comes to living longer and staying healthy for longer.
The findings could be a reason to revamp public health strategies and treatments.
“As a society, we tend to equate body weight or fatness with health status,” said kinesiologist Nathan Weeldryer, from the University of Virginia.
“Our study, which features the largest and most globally representative sample to date, along with more rigorous statistical analysis than previous research, aims to shift perspectives on the relationship between fitness and body fat.”
Researchers from the US and UK compiled and analysed data from 20 studies published during 1980 to 2023, with a total sample size of 398 716 participants. All of the studies included data on body mass index (BMI), cardiorespiratory fitness and mortality risk.
The team found that the risk of an early death for individuals with obesity who were fit was similar to that of people classed as fit and of normal weight. What’s more, having obesity and being fit meant a longer life on average than being a normal weight and unfit.
While the data doesn't show fitness as being the only factor involved, it highlights just how important it is in our overall health. This aligns with previous research linking being fit with a lower mortality risk, though it’s also worth noting that we’re all different when it comes to how exercise affects our bodies.
“Fitness, it turns out, is far more important than fatness when it comes to mortality risk,” says exercise physiologist Siddhartha Angadi, from the University of Virginia.
“Exercise is more than just a way to expend calories. It is excellent 'medicine' to optimise overall health and can largely reduce the risk of cardiovascular disease and all-cause death for people of all sizes.”
The researchers aren't dismissing the health burden of obesity: around one in eight people globally fit the definition of obese now, and the numbers are rising. It puts all kinds of pressures on the body, and increases the risk of high blood pressure, type 2 diabetes, cancers, strokes and diseases of the heart, liver and kidneys.
However, the relationship between obesity and the risk of an early death isn’t clear-cut. The team behind this review wants to see more emphasis on exercise and physical activity and less on weight loss methods.
“Repetitive cycles of losing and gaining weight – yo-yo dieting – are associated with numerous health risks comparable to those of obesity itself,” said exercise physiologist Glenn Gaesser, from Arizona State University.
“Improving cardiorespiratory, aka aerobic, fitness may help avoid the adverse health effects.”
The research was published in the British Journal of Sports Medicine.
Study details
Cardiorespiratory fitness, body mass index and mortality: a systematic review and meta-analysis
Nathan Weeldreyer, Jeison De Guzman Siddhartha Angadi et al.
Published in the British Journal of Sports Medicine in January 2025
Abstract
Objective
The purpose of this review was to assess the joint relationship of cardiorespiratory fitness (CRF) and Body Mass Index (BMI) on both cardiovascular disease (CVD) and all-cause mortality risk.
Design
A systematic review and meta-analysis was conducted. Pooled HR and 95% CI were calculated using a three-level restricted maximum likelihood estimation random-effects model with robust variance estimation. The reference group was normal weight-fit and was compared with normal weight-unfit, overweight-unfit and fit, and obese-unfit and fit.
Data sources
Electronic databases (PubMed/MEDLINE, Web of Science and SportDiscus) were searched following registration on PROSPERO.
Eligibility criteria
Articles meeting the following criteria were included: (1) published between January 1980 and February 2023, (2) prospective cohort study, (3) CRF assessed using a maximal or VO2peak exercise test, (4) BMI reported and directly measured, (5) joint impact of CRF and BMI on all-cause mortality or CVD mortality were analysed, and (6) the reference group was normal weight, fit individuals.
Results
A total of 20 articles were included in the analysis resulting in a total of 398 716 observations. Compared with the reference group, overweight-fit (CVD HR (95% CI): 1.50 (0.82–2.76), all-cause HR: 0.96 (0.61–1.50)) and obese-fit (CVD: 1.62 (0.87–3.01), all-cause: 1.11 (0.88–1.40)) did not have a statistically different risk of mortality. Normal weight-unfit (CVD: 2.04 (1.32–3.14), all-cause: 1.92 (1.43–2.57)), overweight-unfit (CVD: 2.58 (1.48–4.52), all-cause: 1.82 (1.47–2.24)) and obese-unfit (CVD: 3.35 (1.17–9.61), all-cause: 2.04 (1.54–2.71)) demonstrated 2–3-fold greater mortality risks.
Conclusions
CRF is a strong predictor of CVD and all-cause mortality and attenuates risks associated with overweight and obesity. These data have implications for public health and risk mitigation strategies.
See more from MedicalBrief archives:
Obesity paradox: Extra weight offers better survival after a stroke
Doctors dump scales as focus shifts from patients' weight