The pleasure of eating a candy bar lasts but a few minutes. Burning off the calories it delivers can take nearly an hour. So this is definitely not a simple way to lose weight!

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 for this simple way to lose weight

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 increasing 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 about one pound for every extra 35 miles you walk — provided you don't change anything about your current food intake or other activities. 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 altered your diet and cut back by 250 calories a day (1/2 cup of ice cream or two sugar-sweetened sodas), you'd lose a pound in two weeks. If you ate 250 fewer calories a day and walked 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.

For additional information on this and other questions about getting started on a healthy exercise program, read Starting to Exercise, a Special Health Report from Harvard Medical School.

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