Riboflavin status of rats fed two levels of protein during energy deprivation and subsequent repletion.

Adult male rats were fed either a low protein (LP) or moderate protein (MP) diet (0.6 and 1.8 g casein per rat per day, respectively) and 30 micrograms riboflavin (RF) while their energy intakes were progressively restricted to about 30% (26 kcal/day) of the predepletion ad libitum consumption. Total weight losses in 4 weeks averaged 17.3 +/- 0.6 and 12.5 +/- 0.7% from the initial body weights for the LP and MP groups, respectively, despite equal energy deprivation. Although liver riboflavin concentrations (micrograms/gram) were significantly higher in the energy-restricted groups than in either the predepletion or the ad libitum--fed control groups, total liver riboflavin remained at the predepletion level in both restricted groups. During energy deprivation, muscle riboflavin decreased significantly from the predepletion level and was not affected by protein intake. Subsequent repletion with 100 micrograms riboflavin/day and energy at the level voluntarily consumed by the LP group increased body and liver weights with both levels of protein, but liver riboflavin increased only in the MP group. Muscle riboflavin did not return to the predepletion level in either restricted group. Erythrocyte glutathione reductase activity coefficients remained normal for all groups during the depletion-repletion cycle.