Effect of Restricted Water Intake on Urine Nitrogen Output in Man on a Low Calorie Diet Devoid of Protein

¹ From the Laboratory of Physiological Hygiene, University of Minnesota, Minneapolis, Minnesota

Urine nitrogen was measured in three groups of young men receiving, respectively, daily water allowances of 900 ml, 1800 ml and unrestricted quantity. Food was restricted to 1000 Cal. of carbohydrates, 4.5 gm of NaCl and vitamins. The men were required to expend about 120 Cal. daily in walking. The daily urine nitrogen output at the 5th experimental day (adjusted to 70 kg body weight) averaged 9.4 gm for the men on 900 ml of water, 7.1 gm for the men receiving 1800 ml of water and 5.8 gm for the men on water ad libitum. Nitrogen in the feces was unchanged and that in the sweat was either unchanged, or slightly decreased, by water restriction. The increased nitrogen excretion paralleled the degree of dehydration. An elevation of the blood urea nitrogen was observed by the 5th day of combined food and water restriction in the men on 900 ml of water. On rehydration about 3.4 gm of urea nitrogen was washed out, giving rise to a transient continuation of the high urine nitrogen excretion. The increased nitrogen excretion is considered as a metabolic response to the stress of dehydration, partly related to increased activity of the adrenal cortex glands. This catabolic response does not help the body to economize water, as illustrated by the fact that the men receiving the smallest water allowance excreted more urine water than their mates with a more liberal water allowance, at the day of their maximal dehydration.