Each pound of fat your body stores represents 3,500 calories of unused energy. In order to lose one pound, you would have to create a calorie deficit of 3,500 calories by either taking in 3,500 less calories over a period of time than you need or doing 3,500 calories worth of exercise. It is recommended that no more than two pounds (7,000 calories) be lost per week for lasting weight loss.
Adding 15 minutes of moderate exercise, say walking one mile, to your daily schedule will use up 100 extra calories per day. (Your body uses approximately 100 calories of energy to walk one mile, depending on your body weight.) Maintaining this schedule would result in an extra 700 calories per week used up, or a loss of about 10 pounds in one year, assuming your food intake stays the same. To look at energy balance another way, just one extra slice of bread or one extra soft drink a day – or any other food that contains approximately 100 calories – can add up to ten extra pounds in a year if the amount of physical activity you do does not increase.
lf you already have a lean figure and want to keep it you should exercise regularly and eat a balanced diet that provides enough calories to make up for the energy you expend. If you wish to gain weight you should exercise regularly and increase the number of calories you consume until you reach your desired weight. Exercise will help ensure that the weight you gain will be lean muscle mass, not extra fat.