It is apparent from recent studies on fasting as an introduction to the treatment of obesity 1 that the weight loss in fasting patients was greater than could be explained on a caloric basis. Preliminary studies indicated that salt excretion significantly exceeded that observed in patients on low-salt diets. The potential importance of these observations was obvious, and quantitative studies were performed on fasting obese patients in an attempt to elucidate the unexplained weight loss. Benedict's2 early studies on Levanzin, the professional faster, indicated that weight loss in fasting was greatest during the early fast period. Gamble, Ross, and Tisdale3 suggested that early in fasting there was a loss of extracellular fluid, loss of water from reduction in cell volume and water loss from metabolism of cell substance, and these multiple factors accounted for the weight loss in excess of caloric expenditure. Gamble4,5 and Hervey and McCance