To burn 1 pound of body fat, a person weighing 150 pounds has to walk 39 miles at an average pace of two miles per hour, burning 90 calories per mile. It takes 26 miles when walking at a pace of 3.5 miles per hour at 135 calories per mile.
To lose 1 pound of fat, you must burn 3,500 calories. Depending on your body weight, you can burn anywhere from 90 to 360 calories during 30 minutes of moderate to vigorous walking exercise and burn fat safely over time, without walking 25 to 39 miles at once. Eliminating 3,500 calories from your total caloric intake each week also burns 1 pound of body fat.