Early weight gain by starving patients managed with total parenteral nutrition has been regarded as spurious - that is, merely an increase in body water. We designed an experiment to mimic the starved state in which glycogen stores are depleted and sodium intake is very low. The subjects were then repleted with a sodium-free, high carbohydrate intake. All subjects who received potassium gained weight and switched to a respiratory exchange ratio which suggested mainly carbohydrate oxidation. From changes in weight and total body water the weight gain was calculated to be the consequence of glycogen storage with 1 g of glycogen obligating 3.21 +/- 0.57 g water. Two patients with total dysphagia showed a similar pattern. Two subjects who did not receive potassium showed a rise in respiratory exchange ratio but failed to store glycogen. Early weight gain in patients who received high-carbohydrate feeding after starvation is a normal phenomenon and represents a return to a more hydrated state consequent upon glycogen repletion.