You can't be severely overweight and still be physically fit, scientists have argued.
New research found that obese people who exercise regularly were more likely to die prematurely than slim people, even if the latter did little exercise.
The Swedish study followed 1.3 million men of various body types for an average of 29 years.
It found that those who were obese with high levels of aerobic fitness were 30% more likely to die prematurely than participants who were slim and rarely exercised.
In the study, published in the International Journal of Epidemiology, the researchers said that overweight people can't compensate for their weight by completing exercise, busting the myth that a person can be "fat but fit".
Professor Peter Nordstrom, of Umea University, Sweden, commented: "Unfit normal-weight individuals had 30% lower risk of death from any cause than did fit obese individuals.
"These results suggest low BMI (body mass index) early in life is more important than high physical fitness, with regard to reducing the risk of early death."
That's not to say that exercise is not beneficial to health.
The study found that men who had the highest level of aerobic fitness were 48% less likely to die from any cause when compared to those who had the lowest level of aerobic fitness.
This statistic included having a lower chance of death from alcohol consumption, heart disease and suicide.
However, the benefits of exercise were cancelled out when the men were also classed as obese.
The latest study comes after England's chief medical officer Dame Sally Davies named obesity as the "biggest threat" to women's health.
"Obesity has to be a national priority. Action is required across all of society to prevent obesity and its associated problems from shortening women's lives and affecting their quality of life," she said.
"We need to address the educational and environmental factors that cause obesity and empower women and their families to live healthier lives."