American Journal of Clinical Nutrition, Vol 19, 320-328, Copyright © 1966 by The American Society for Clinical Nutrition, Inc.

Fasting and Refeeding of Various Suboptimal Isocaloric Diets

Effects on Mineral and Nitrogen Balances in Obese Patients

¹ From the West Virginia University Medical Center, Department of Medicine, Morgantown, West Virginia

Mineral and nitrogen balance studies were carried out in six obese patients during short-term fasts and refeeding with suboptimal isocaloric diets composed primarily of carbohydrate, fat and essentially equal mixtures of protein, fat and carbohydrate. Two patients were studied during the ingestion of diets containing only protein. Sodium and nitrogen retention were greatest during refeeding with carbohydrate-containing diets. A diet composed largely of fat did result in sodium and nitrogen retention, but at a slower rate and to a lesser degree than observed with diets containing substantial amounts of carbohydrates. Sodium and nitrogen retention with the fat diet were greatly potentiated by prior carbohydrate feeding. Plasma ketones increased during fasting, were maintained at high levels during refeeding with fat diets, and decreased quickly towards normal with carbohydrate diets. The rate of decline and degree of reduction of plasma ketones were directly correlated to the carbohydrate content of the diets. Calcium balance and urinary excretion of calcium appeared to be directly correlated to the degree of ketosis. Even though fasting may activate mechanisms leading to maximum nitrogen retention on refeeding, fat is unable to initiate nitrogen retention nearly as effectively as carbohydrate or protein.