The impact of physical training on body weight and fat depends on the ability of exercise to promote a negative fat balance. This effect is more likely to occur in individuals who are good responders in fat oxidation to exercise and who adhere to a dietary regimen containing a low to moderate amount of fat. Experimental evidence suggests that exercise per se may also increase the preference for carbohydrates, i.e. reduce the relative fat content of the diet, and this might be related to the composition of the substrate mix oxidized during exercise. The body fat loss resulting from a long-term negative fat balance is associated with a progressive decrease in fat oxidation which is likely involved in the occurrence of resistance to lose fat in reduced obese individuals. This suggests that fat loss related factors represent signals for neurosystems controlling feeding behavior. Further research pertaining to exercise and the control of food intake should focus on the mechanisms by which exercise may influence neurosystems which are known to affect food intake.