The diet-exercise link: separating fact from fiction.

The diet/exercise link: separating fact from fiction Even those who pay scant attention to what's up in the world of fitness know that exercise is an essential part of any "diet" geared toward maintaining good health. They also, unfortunately, accept a good many diet/exercise maxims as common "knowledge" whether they are true or not: eating more protein builds stronger muscles; the bathroom scale is the best gauge for determining whether a fitness program is working; vitamin supplements are a must for the novice exerciser trying to build up stamina. How many such sayings have you swallowed wholesale?

The best reason to exercise is to burn calories. That's only part of it. Physical activities that increase the heart rate, such as brisk walking, jogging, swimming, fast dancing, and biking, can also increase HDL-cholesterol (the "good," artery-friendly kind); increase bone mass somewhat and thereby possibly provide resistance to osteoporosis; cut down on anxiety and stress, apparently by releasing opiate-like chemicals in the brain; and enhance overall cardiovascular fitness. They can also prevent or alleviate constipation; the muscles of the large intestine appear to remain in better shape when the other muscles of the body are "worked." Exercises that do not increase the heart rate significantly--weight lifting, stretching, and the like--do not directly bring about all these benefits, but in improving the strength and flexibility of the muscles, they enhance the capacity to perform the activities that do.

No pain, no gain. If belief in this maxim stands between the decision to improve your physical fitness through exercise or to continue leading an unhealthfully inactive lifestyle, take note: You needn't resort to marathon training sessions or push yourself until it hurts to enjoy the benefits of physical activity. In fact, excessive exercising increases the chances of bone, joint, and muscle injury, not to mention making the workout seem more like punishment than pleasure. For most people, simply exercising for 15 to 60 minutes three to five times a week at a pace that will allow your heart rate to fall within your "training zone" (your doctor can help you determine that "zone" exactly) is all that's needed to reap significant health benefits. Even individuals who are counting calories will profit, since seemingly modest amounts of calories burned through consistent exercising add up relatively quickly. Consider that while the energy used in 45 minutes of brisk walking accounts for only…