Use of a new vitamin C-deficient diet in a depletion-repletion clinical trial

Abstract

To conduct an inpatient study on the recommended dietary allowance (RDA) for vitamin C, we developed a unique vitamin C deficient diet using a nutrient database and selective menus. Fourteen different menus were developed offering > 300 items with 0-2.4 mg vitamin C per serving. During the 4-6 mo volunteers were hospitalized, daily dietary vitamin C was restricted to ≤ 5.0 mg. The mean daily dietary vitamin C intake was < 3.9 mg for the seven study subjects. With concurrent supplementation, the diet provided ≤ 85% of the RDA for 17 essential nutrients. Within 3 wk of admission the diet induced vitamin C deficiency as indicated by plasma concentrations, which decreased from 23 ± 6.9 to 6.9 ± 2.0 μmol/L. Daily intake of vitamin C and five other nutrients was determined by nutrient database analyses. Mean energy, protein, and iron were 105-185% of the RDA and total and saturated fat were 32% and 10% of energy, respectively. Weight and nutritionally relevant indexes remained normal. Dietary adherence, calculated by the number of days with ≤ 5.0 mg vitamin C per total study days, was 88-98% per repletion dose. Computer analyses of menu selections permitted individual preferences to be met while restricting vitamin C intake to ≤ 5.0 mg/d. There were no complications from the diet during the depletion and repletion phases. With this diet, ascorbic acid pharmacokinetics for escalating doses could be determined in healthy volunteers.