They are usually less active. Their bodies are less efficient at burning calories and more efficient at storing them. Fit people burn extra calories before any can be stored as fat in the body. Overweight people store extra calories as fat. Exercise changes metabolism.
Regular exercise allows overweight people to lose fat and control their weight.
What activity, how often, how hard, and how long are important questions to ask when adding exercise to your lifestyle. The most effective workout program includes both aerobic exercise and strength training. The combination yields faster fat loss at any age. Aerobic exercise increases metabolism. Strength or weight training builds muscle.