The number of calories used up by exercise is often less than expected, but despite this, it is much easier to reduce your weight, and also avoid gaining weight, if you exercise regularly.
Our bodies are made for movement. Our ancestors devoted most of their time to physical activities. The normal weight regulation system works better if we exercise. Overweight occurs when this system fails to give us the correct signals, making us want to eat even when we should be satisfied. Physical activity helps our bodies feel hunger and satisfaction in the right way. A combination of exercise and avoidance of fat and junk food, which distort our ability to feel satisfaction, is important. The effect of exercise on food intake was first discovered during research on rats. The rats were allowed to exercise at different times per day and it was found that when they exercised for one hour or more, their eating increased in accordance with their calorie requirements, but when they exercised for less than one hour, they still ate more than they needed. The body's natural weight regulation no longer functioned when they exercised for less than one hour. Practical experience indicates that exercise also makes it easier for us to maintain a constant weight. We eat less if we exercise. (Plus, it is impossible to eat while exercising!)