for reasons explained below, the recommendation to you is to use a combination of the two to achieve your goal. When you reduce your caloric intake, your body responds as if you are beginning to starve. One of the body's adaptations is to decrease the resting metabolic rate to save the body's energy stores. This means that a diet very low in calories can become counterproductive to weight loss; the more you cut back on caloric intake, the more the body responds by decreasing its energy expenditure.
When you lose weight by alone, 35 to 45 percent of the weight lost is lean tissue, not fat tissue. Therefore, you could actually lose weight but not change your percent of body fatness (body composition) very much. This loss of lean tissue also contributes to the body's reduction in resting metabolic rate, making it more difficult for you to lose weight. Resistance training can increase muscle mass and help maintain the resting metabolic rate. A weight-loss program that uses diet alone results in a slower rate of fat loss. It should be no surprise, then, that a combination of diet and exercise is recommended to achieve weight-loss and body-composition goals. Exercise helps to maintain lean muscle tissue and the resting metabolic rate while more fat is being lost; the body actually makes changes in percent body fat faster than it can through diet alone. There are many cases in which body weight may not change for several weeks but clothing sizes do. The exercise is increasing lean body mass while fat mass is decreasing slightly. With time, body weight will decrease in proportion to the change in energy balance.
Exercise and Weight Management:
The present information proves that exercise is a very beneficial part of your lifestyle, whether you are losing weight or not. The body expends energy whether at rest, work, or play. A person must take in and use oxygen (O2) for this to occur. In fact, if we know how much oxygen is being used, we can calculate how many calories of energy the body expends. The body's use of one liter of oxygen causes the expenditure of five calories of energy. This is a very important point in understanding the role of exercise in weight loss. There should be a negative caloric balance of 3,500 calories which is necessary to lose one pound of fat tissue. For example, imagine there are two people trying to lose weight one by sitting in a sauna and the other by running around a track.
The person sitting in the sauna expends only 72 calories per hour because the body uses very little oxygen while sitting at rest. The person running around the track, however, expends about 600 calories per hour because the body requires a great deal of oxygen to run. To expend the caloric equivalent of one pound of fat (3,500 calories), it would take 50 hours of sitting in a sauna but only 6 hours of running.