How long should you walk to lose weight?

You start burning calories, above basal metabolism, the moment you start moving but you don't start burning fat until at least after 20 minutes of a raised heart rate. Before those 20/30 minutes, normal energy and sugars are burnt whereas after that amount of time, the body will be looking at its fat storage for energy. Studies have shown that short walks spread over the day are as beneficial as one long walk of the same total duration.