Need to lose weight? Cutting back on calories consumed while bumping up total activity level is the most effective method.

Wolfing down a candy bar takes a mere minute or two; walking off those calories would take most people about 40 minutes. To lose a single pound, you need to burn approximately 3,500 calories. Doing so through activity alone could easily take a few weeks of regular, moderate exercise. On the other hand, consuming 500 fewer calories a day will result in the loss of a pound a week. For that reason, dieting alone seems as though it would be a fast path to weight loss.

But regular exercise offers certain benefits beyond calorie burning. It slightly increases your resting energy expenditure— that is, the rate at which you burn calories even when the workout is over and you are at rest. And pounds lost through boosting your activity level consist almost entirely of fat. Plus, some studies suggest exercise preferentially targets abdominal fat, which plays a role in hypertension, cardiovascular disease, and diabetes.

Counting calories: What it takes to burn a pound of fat

For easy exercises that will achieve results, purchase Exercise – A Program You Can Live With from Harvard Medical School.

How vigorously should I exercise?

Whether you are healthy or have medical issues, moderate activity is safe for most people and does plenty to improve your health. If you're in good shape, adding vigorous activities to your workouts cuts time spent exercising and is a boon to health. If you're not fit, work up to vigorous activities slowly. Higher-intensity activities raise your chances for muscle or joint injury and very slightly increase the odds of developing a serious heart problem. This applies particularly to people who are unaccustomed to physical activity, who suddenly start exercising vigorously (although the overall risk of dying from heart disease is lower than if you did no exercise).

How can you judge the pace of your workout? The easiest way to measure exertion characterizes the intensity of an activity through broad categories, such as light, moderate, or vigorous. Called perceived exertion, it's especially helpful for staying in a safe range of activity. As you improve your fitness, you'll find your perception of the intensity of a particular activity—walking up a nearby hill, for example—changes.

The table below describes physical changes at each level of exertion. If you're just getting started with an exercise program, aim for a moderate pace. (If health problems or disabilities make moderate activity impossible, simply do as much as you can.) As you build up, try a mix of moderate and vigorous activities to help build endurance. As you work out more often, you'll notice gains as exercises become easier. Whenever an activity becomes easy, boost the length of your workout or your intensity again.

For additional information on this and other questions about starting a healthy exercise program, purchase the Special Health Report, Exercise, A Program You Can Live With from Harvard Medical School.