How Effective Is Exercise in Producing Fat Loss?

Over the past quarter century obesity has reached epidemic proportions in many developed countries. Exercise is one of the behavioral approaches to curbing weight gain or losing body fat. We reviewed the data on (1) magnitude of weight and fat loss when exercise is implemented without any changes in food intake, (2) necessary volumes and intensities of exercise to accomplish and sustain weight and fat loss, (3) effects of obesity on spontaneous physical activity and other forms of energy expenditure, (4) effects of obesity and aerobic fitness on the capacity to oxidize fat, and (5) the effects of exercise on the appetite. When exercise is implemented without any changes in food intake, a daily expenditure of 400 Kcal produces a fat loss that is about one third of that expected on the basis of caloric deficit incurred by exercise. Oxidation of fat is negatively influenced by exercise intensity so that for an appreciable fat loss it would be necessary to exercise for long periods of time. Genetics and low aerobic fitness can also play a negative role. Obesity is associated with low levels of spontaneous physical activity and reduced capacity to oxidize fat. Aerobic training can enhance the capacity to oxidize fat by increasing the volume and function of mitochondria in skeletal muscles. Exercise is associated with short-term suppression of hunger and a failure to compensate for exercise energy expenditure during the hours to several days following exercise. Exercise is advisable as an approach toward fat loss, even more so when it is associated with dietary restraint, because it improves fat oxidation, saves lean body mass, and does not immediately stimulate hunger.