Full disclosure: I am posting this in its entirety directly from the HEALTHbeat newsletter of the Harvard Medical School because it is quick, clear and worth knowing. RR
The pleasure of eating a candy bar lasts but a few minutes. Burning off the calories it delivers can take nearly three-quarters of an hour.
To lose one pound by exercising, you need to burn approximately 3,500 calories. It can take days of moderate exercise to do this. A better strategy for weight loss involves a two-pronged approach: exercising and cutting calories.
Although exercise by itself isn’t the fast track to weight loss, it does offer important benefits beyond cancelling out calories. It slightly increases the rate at which you burn calories even when you’re not working out. And pounds lost through boosting your activity level consist almost entirely of fat, not muscle.
Do the math
Start with this number: 3,500. That’s how many calories are stored in a pound of body fat. With that number you can tally up how much weight you can lose through activity, cutting calories, or both.
Walking or jogging uses roughly 100 calories per mile. (Precisely how many calories you’ll burn depends on a number of things, including your weight and how fast you walk.) So you’d lose a pound for every 35 miles you walk — provided you keep food intake and other activities constant.
If you walk briskly (at a pace of 4 miles per hour) for 30 minutes on five out of seven days, you’ll log 10 miles a week. That means it would take three-and-a-half weeks to lose one pound if the number of calories you consume stays the same.
If you alter your diet and cut back by 250 calories a day (½ cup of ice cream or two sugar-sweetened sodas), you’d lose a pound in two weeks.
By eating 250 fewer calories and walking for 30 minutes a day, it would take just over a week to lose one pound. Reducing calorie intake even more and exercising more would further speed the process.