There are several studies on the effect of overfeeding and underfeeding on physical activity as measured under free-living conditions with doubly labeled water.the effect of overfeeding on physical activity, calculated by expressing total energy expenditure as a multiple of resting energy expenditure is non-significant.There does not seem to be an effect of overfeeding on physical activity, when overfeeding is lower than twice maintenance requirement, as observed in studies lasting up to 9 weeks.