Obesity is often considered one of the most important factors in the likelihood of early death, but a new 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,” says 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 compared to previous research, aims to shift perspectives on the relationship between fitness and body fat.”

Researchers from the US and UK compiled and analyzed 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 optimize 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 1 in 8 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,” says exercise physiologist Glenn Gaesser, from Arizona State University.

“Improving cardiorespiratory, aka aerobic, fitness may help avoid the adverse health effects.”

The research has been published in the British Journal of Sports Medicine.