While it is possible to lose weight with physical activity alone, the amount of physical activity required for substantial weight loss is well beyond what is feasible for most Americans. Wing  reviewed several studies in which physical activity alone was used for weight loss. While the amount of weight loss with physical activity was significantly greater than 0, it was in the order of only a few pounds.
Similarly, Wing  reviewed several studies in which weight loss with diet alone was compared with weight loss with diet plus exercise. It was concluded that most studies found no significant differences in total weight loss but that in just about every study the absolute amount of weight lost was a little higher when diet and exercise were used. This is not surprising given that weight loss is a function of the degree of energy imbalance and that a much greater energy imbalance can be created with food restriction than with increased physical activity.
Even though adding physical activity to food restriction adds little when it comes to initial weight loss, there may be other advantages of engaging in physical activity during weight loss that increase the chances that the weight loss will be maintained. Physical activity could result in a higher proportion of weight loss coming from fat and less from fat-free mass loss . This could reduce the drop in metabolic rate that accompanies weight loss. Another advantage of engaging in physical activity during weight loss is that it may better prepare the person to be able to engage in sufficient amounts of physical activity to keep weight off.
Role of Physical Activity in Maintenance of Weight Loss
In many studies, high levels of physical activity have been found to predict success in long-term weight loss maintenance [19-22]. For example, subjects in the National Weight Control Registry who are maintaining an average weight loss of about 30 kg for about 5.5 years, report expending about 2,800kcal/week (—60-90 min/day) in physical activity . Less than 10% of the successful weight loss maintainers report that they are maintaining their weight loss with diet alone. Decreases in physical activity in this group predict weight regain over time. Others [20-22] have found that amounts of physical activity equivalent to about 60-90 min/day are associated with successful weight loss maintenance.
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