EXERCISE

Many people exercise to lose weight. A calorie is a unit that measures the energy content of foods and the energy expenditure by the body. When the daily calorie intake from food is the same as calories expended from exercise, weight remains the same. The number of calories burned during exercise varies greatly with the type of physical activity, but the key to successful weight reduction is to exercise regularly, without increasing food intake proportionally. For example, walking one hour per day may utilize only 300 calories of energy per day, a small fraction of an individual's daily caloric intake. But over a period of time, if food consumption is simultaneously reduced or remains the same, significant weight loss will result. One sound approach to reducing calories is to eat healthier foods that contain more fiber and less fat, and therefore fewer calories. This type of diet has also been proven healthier for the heart and blood vessels.

One area of controversy has been how much exercise is enough to improve general health, reduce the risk of heart disease, and increase longevity. Meaningful studies on this topic are very difficult to perform because they require large populations of subjects and many years of data collection, and because poor health sometimes results in limitations to physical activity. Despite these difficulties, it is clear that regular exercise, along with a generally healthy lifestyle, is beneficial. People who have sedentary lifestyles make up half the population of industrialized societies, and this group has the most to gain by exercising. One recent U.S. National Institutes of Health (NIH) panel suggested that as little as 30 minutes every day of purposeful, moderately strenuous physical activity—for example, rapid walking or lawn mowing—is sufficient to lower the risk of heart disease. There is no conclusive evidence to prove that an especially rigorous exercise routine, such as running many miles per day, as opposed to walking or jogging daily, will add years to a person's life.