A brisk 30-minute walk five days a week is more effective than any other form of exercise for keeping weight down regardless of age, a major study has concluded. The effectiveness of ‘high impact’ walking in keeping weight down is greater than that from keep-fit activities including running, swimming and working out in the gym. Men who walked briskly for 30 minutes five days a week for four weeks had a BMI one unit lower than average; for women the difference was 1.8 units. For those who exercised or participated in sporting activities over similar periods, however, the results were less marked: men’s BMI was 0.3 units lower and women’s about one unit lower. The explanation for this is likely to be that calorie burning is optimised when walking because it is a constant, uninterrupted activity, unlike games such as tennis which are more stop-start.