Answer:
There is no generally agree-upon answer. However, I suggest that you think of brisk walking as walking at a 4 mile per hour pace. To avoid gaining body fat as you get older, you will probably find that averaging walking two miles daily is sufficient.
If you want to use brisk walking to decrease your amount of body fat, walk 3, 4, 5, or 6 miles daily. You do not have to do your daily walking all at one time; you may go for two or three walks. The best time to walk is before your first meal of the day. Of course, you should obtain your physician's blessing before making any significant changes to your diet or exercise program. If you have not been walking regularly, start slowly.