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Utilization of Calcium, Phosphorus, Riboflavin and Nitrogen on Restricted and Supplemented Diets¹

Agricultural Experiment Station and College of Home Economics University of Tennessee, Knoxville

On diets devoid of milk, eggs and wheat and furnishing approximately 300 mg of calcium, 800 mg of phosphorus and 1.0 to 1.5 mg of riboflavin per day, all subjects were in definitely negative calcium balance while mean retentions of phosphorus and riboflavin approached equilibrium.

Supplementation of the restricted diets with dicalcium phosphate and riboflavin or with milk, eggs and wheat gave daily intakes of 1.0 to 1.4 gm of calcium, 1.3 to 1.7 gm of phosphorus and 1.9 to 3.5 mg of riboflavin. Utilization of all three nutrients was more efficient when the supplement was supplied by natural foods than by the mineral and synthetic vitamin. The decreased availability of calcium and phosphorus from the mineral source resulted from smaller absorption of calcium and phosphorus from the intestinal tract. The restricted diets became adequate to maintain all subjects in positive balance with respect to calcium and phosphorus when the CaHPO₄ supplement raised the daily calcium intake to approximately 1.4 gm.

Riboflavin excretions appeared to be directly related to intake. Retentions increased significantly with intake without any indication that maximum retention had been reached. The data were interpreted to mean that these young women were able to utilize dietary riboflavin at levels well above the recommended 1.4 to 1.9 mg per day.

Mean nitrogen retentions were positive throughout all periods with daily intakes of 9.9 to 11.1 gm. Extrapolation of the regression line for retention on intake indicated that 8.6 gm of nitrogen or 54 gm of protein per day was required to maintain equilibrium in these subjects.

Manuscript received 24 October 1955.