A brisk 30 minute walk - five days a week - is more effective than any other form of exercise for keeping weight down.
Researchers at the London School of Economics and Political Science have found the benefits of high impact walking outweigh those from running, swimming and working out in the gym.
But walkers must walk quickly enough to raise the heart rate and cause sweating.
The results are particularly strong for women of all ages - with those walking for half an hour found to be on average a dress size smaller.
I've been speaking to Dr Grace Larden - who lead the study - about the research:
