Before we discuss the benefits of fast walking let's define what 'fast walking' actually is. In this instance fast walking doesn't necessarily mean walking at a fast pace but rather walking after a fast; taking a walk prior breakfast for example.
Why should I walk before breakfast?
When we sleep we still burn calories and deplete our blood sugar levels, which means that taking a walk ebfore breakfast is more likely to burn body fat rather than rely on blood glyogen or muscle glycogen for energy - the energy. This means that overweight people, or people looking to drop that last percentage of body fat to display a six-pack will benefit from walking (at a moderate pace) before eating any food for that day.
How much fast walking should I do?
This depends on the amount of body fat you need to lose. For those overweight, 30 minutes 5 times a week will help (followed by a calorie controlled diet of course) whilst those looking to reveal their abs my benefit from 30-40 minutes 3-5 times a week; though up this level or decrease it depending on the results you get.
Follow this plan for 6-12 weeks to see real weight loss and health benefits.
Monitor your energy levels
That said, exercise of any kind before breakfast can be tiring so make sure that fast walking doesn't sap your energy too much. After the walk you should feel good rather than too tired to tackle a normal working day or any other exercise that you have scheduled into your day.