Walking or running can help you lose weight as fast as almost any activity, but the key to weight loss is how many calories you’re burning when you exercise. Calorie burning relates to the intensity of the activity and the duration. If you’re going to cover 4 miles a day, you will lose weight immediately, simply by burning hundreds of calories with each run. That's assuming, of course, you don’t start eating more and more every day. The speed at which you lose weight, however, will depend on how many of those miles are run or walked.
Losing weight is all about burning more calories than you consume, and 3,500 calories equates to about 1 pound. So if you walk or run off 500 calories every day for a week, you’ll lose around 1 pound per week. For example, a 200-pound person running 4 miles a day would burn a little more than 500 calories during that run. That's assuming he's running at 6 mph for about 35 minutes. Walking at 3 mph for about 80 minutes would also cover about 4 miles and would burn more than 950 calories. Even though walking is less intense, if you cover the same amount of ground, you'll ultimately lose more weight by walking. It will just take longer each each day.
In the 1990s, when people stared to use pedometers to track their steps, the idea of walking 10,000 steps a day was used in the marketing of the devices. The figure amounts to between 4 and 5 miles, depending on the length of your stride. While there is nothing particularly special about that distance -- other than that it’s a nice, round number -- a person who is walking briskly can walk about 4 mph. That means you can get your 10,000 steps, or 4 miles done in about an hour.
There is some dispute whether the longer time spent walking a certain distance, as compared to the time spent running the same distance, actually burns more calories because you're actively engaged longer. However, it takes about twice as long to walk a specified distance as it does to run that same route. So if you're looking to save time with your workout, crank up the speed from a walk to a run to maximize your efforts.
Running 4 miles a day will help you lose weight in a hurry. But don't discount walking 4 miles a day, especially if you are recovering from a joint accident or other physical ailment that might lead to restricted physical performance. While running 4 miles a day may seem like a great idea at first, check with your doctor about any limitations you should consider. And you can always start out walking, before moving on to running, to help burn more calories in a given time period.