Doing some activity is great, but if you can walk as fast as you can for even just 15 seconds during your walk every few minutes, it tends to help more than just plodding along at the same pace for a longer time. In the Supercharged South Beach book, it talks about interval training, and you seem to get the same results in a shorter time period..the plan is just to exercise for 20 minutes a day, although I like taking long walks, for exercise and clearing my mind. Good luck!