Lack of exercise is twice as likely to lead to an early grave than obesity, research has shown.
A brisk 20-minute walk each day is all it takes to avoid dying prematurely, the findings suggest.
Scientists looked at the effects of obesity and exercise on 334,161 European men and women whose progress was followed for 12 years.
They found that people who engaged in moderate levels of daily exercise - equivalent to taking an energetic 20-minute walk - were 16 per cent to 30 per cent less likely to die than those classified as inactive.
Although the impact of exercise was greatest among normal weight individuals, even those with high Body Mass Index levels saw a benefit.
Overall, avoiding inactivity theoretically reduced the risk of death from any cause by 7.35 per cent, said the scientists.
Having a BMI lower than obesity levels, defined as a score of 30 or more, was estimated to lower mortality by 3.66 per cent.
Keeping waists trim, irrespective of BMI, had a similar impact on death rates as exercise.
Lack of exercise was thought to have caused almost 700,000 deaths across Europe in 2008
BMI is calculated by dividing a person's weight in kilograms by their height in metres squared and is a standard tool used to assess whether someone is overweight or obese.
At the population level, lack of exercise was thought to have caused almost 700,000 deaths across Europe in 2008.
Study leader Professor Ulf Ekelund, from the Medical Research Council (MRC) Epidemiology Unit at Cambridge University, said the simple message is that just a small amount of physical activity each day could have substantial health benefits for people who are physically inactive.
"Although we found that just 20 minutes would make a difference, we should really be looking to do more than this - physical activity has many proven health benefits and should be an important part of our daily life," Prof Ekelund said.
Participants in the research, who had an average age of around 50, were all recruited to the European Prospective Investigation into Cancer (Epic) study conducted across 10 European countries, including the UK.
All had their height, weight, and waist sizes measured and provided self-assessments of physical activity levels.
Just under a quarter (22.7 per cent) were categorised as inactive, working in sedentary jobs without engaging in any recreational exercise.
The greatest reductions in the risk of premature death were seen when comparing moderately active groups with those who were completely inactive.
Using the most recent available public data, the researchers calculated that 337,000 of the 9.2 million deaths that occurred in Europe in 2008 could be attributed to obesity.
But physical inactivity was thought to be responsible for almost double this number - 676,000 deaths.
The findings are published in the American Journal of Clinical Nutrition.
Co-author Professor Nick Wareham, director of the MRC Epidemiology Unit, said helping people to lose weight should continue, with the aim of reducing population levels of obesity, but encouraging changes in physical activity which could have significant health benefits may be easier to achieve and maintain.
