About 10,000 cases of breast and bowel cancer could be prevented each year in the UK if people did more brisk walking, claim experts.
The World Cancer Research Fund scientists say any moderate activity that makes the heart beat faster should achieve the same.
For example, data suggest 45 minutes a day of moderate exercise could prevent about 5,500 cases of breast cancer.
Physical exercise helps prevent obesity, which is a cancer risk factor.
The WCRF team stress in their report that it is the total time spent being active that is important. You do not need to set aside half an hour each day to exercise. Shorter bouts of activity will be just as beneficial as long as they add up to the same, the charity says.
Alongside brisk walking, other activities that would count include cycling or swimming at a leisurely pace, dancing, gardening and vacuuming combined with other housework, says the WCRF.
Their head of science, Dr Rachel Thompson, said by making small changes to their daily routine people could achieve significant health gains.
"There is now every strong evidence that being physically active is important for cancer prevention.
"Even relatively modest increases in activity levels could prevent thousands of cancer cases in the UK every year.
"These figures also show you do not have to go to the gym every day to benefit.
"You can reduce your cancer risk just by making small changes and this is highlighted by the fact that so many cancer cases could be prevented through something as simple as brisk walking.
"By taking up walking as a hobby or even walking to the shops instead of taking the bus or car, people can make a real difference to their health."
Henry Scowcroft, science information manager at Cancer Research UK, said: "You don't have to be an athlete to reduce your cancer risk.
"There's solid evidence that certain cancers - including breast and bowel cancer - are less common in people who do regular, moderate exercise such as brisk walking."