Most runners have heard that running burns about 100 calories per mile.
And I used to believe since walking a mile requires you to move the same body weight over the same distance, walking should also burn about 100 calories a mile. Sir Isaac Newton said so! When I first started running I had this 4 km loop that I would repeat over and over again. One day I remember thinking to myself; "Slow down! You just have to finish and then you will have burned the same amount so why bother pushing harder?"
In "Energy Expenditure of Walking and Running," published December 2005 in Medicine & Science in Sports & Exercise, a group of Syracuse University researchers measured the actual calorie burn of 12 men and 12 women while running and walking 1,600 meters (roughly a mile) on a treadmill. Result: The men burned an average of 124 calories while running, and just 88 while walking; the women burned 105 and 74. (The men burned more than the women because they had more muscle mass.) That difference adds up over the miles and weeks running vs. walking.
Running: .63 x your weight (lbs) x miles = net calories burned
Walking: .30 x your weight (lbs) x miles = net calories burned
Picking up the pace is also better for your heart, you won't necessarily see the same heart healthy benefits if you walk to keep your weight down over running. The high intensity aspect running delivers is so important, your heart needs to learn how to deal with stress and get stronger from that. Walking just won't stress it out enough.
I rarely, if ever run the same loop twice now. Variety is essential for exercise. I recently went back and did a similar variation of my initial route and I was done with 15 minutes to spare! I felt energized and was happy to get it over with quickly! So pick up the pace! Your heart and waistline will thank you for it.