Running can scorch calories, but that doesn't mean you'll drop pounds rapidly. What you eat between those runs, your current size and your fitness level all affect how quickly you lose weight. Running on the treadmill every day is only part of your weight-loss strategy. Excessive running on the treadmill my even be counterproductive to your goals.
How You Lose Weight
Weight loss occurs when your energy output exceeds your energy intake. A 3,500-calorie deficit is generally accepted as being what you need to achieve to lose 1 pound. Most people achieve this deficit with a combination of calorie restriction and increased calorie burning through movement.
Calorie Burn Numbers
If you run every day of the week, you'll have to burn 500 calories in each of those runs just to lose a pound per week. If you weigh upwards of 180 pounds, you'll burn slightly more than 700 calories per hour going at a 5 mph pace -- resulting in a potential 1.4-pound per week weight loss if not undercut by overeating. If you weigh 150 pounds, you'll burn more like 600 calories in that hour, for a 1.2-per-week weight loss. The more you weigh, the more calories you burn with each step you take. You'll also burn more calories the faster you run. For example, a 180-pound person burns almost 1,000 calories per hour running at a 6.7-mph pace, or a nine-minute mile.
Not That Easy
You might think, then, if you run at a pace of 5 mph for three hours per day, every day during the week, you could burn off 4 or 5 pounds per week -- which when compared to the recommended 1 to 2 pounds per week -- is rapid. Chances are, however, if you are large enough to burn 600 to 800 calories per hour running at a modest pace, your joints will not appreciate the impact. If you're extremely overweight, you're probably not in shape enough to sustain that level of activity, either. Even the lightest of marathon runners rarely run three or more hours per day; it simply takes too much time, energy and effort.
More Harm Than Good
By running dozens of hours per week, your body will compensate by becoming more efficient, so you'll end up burning fewer calories with each run and storing more fat because your body is under such tremendous physical stress. Your appetite will also respond to the tremendous change in energy output and you might find yourself disproportionately hungry -- so ravenous that restricting your calories is simply impossible. Your body will likely burn out after just a few days of attempting long runs on the treadmill and you'll be vulnerable to injury. Treadmill running for hours may also leave you so tired that you fail to burn calories with all-day activity, such as taking the stairs, cooking dinner, cleaning the house, walking through the parking lot and playing with your kids.
Without significantly changing your diet, exercise -- even hours of running on the treadmill -- will most likely not lead to major, rapid weight loss. You need to curb your calorie intake and make the calories you do ingest come from healthy, natural foods like vegetables, fruits and modest amounts of whole grains, proteins and healthy fats to ensure you get all the nutrients you need to be healthy. Instead of seeking rapid weight-loss through running on the treadmill, set a reasonable, sustainable strategy for yourself. Trim your calorie intake daily by 500 to 700 calories and aim to burn 300 to 500 calories daily most days per week to lose 1 to 2 pounds per week. Steady-state running on the treadmill is only one type of workout you should include. Resistance training, stress-relieving activity such as yoga and shorter interval workouts should all be part of your weight-loss workout strategy.