The effect of dietary protein source on manganese bioavailability to the rat

Rats were fed diets containing 20% protein from casein, beef, chicken, tuna, or soybean. All diets contained 15% fat and were supplemented with limiting amino acids as necessary to meet National Research Council requirements. In Experiment 1, the manganese content of all diets was the same; manganese content was 5 mg/kg. In Experiment 2, a basal (adequate) level of minerals was provided in each diet but total mineral content varied depending on the contribution of the protein source; manganese was added to achieve a concentration of 5 mg/kg. In both experiments, 54Mn absorption was greatest from tuna (8.54% and 7.71%) and least from beef (4.57% and 4.14%) (P less than 0.0001). In both experiments, biologic half-life of 54Mn was longest in rats fed beef (18.5 and 26.9 days) and shortest in rats fed soy (14.5 and 16.2 days) (P less than 0.0002). Except for beef, biologic half-life was similar for dietary groups between the two experiments. In Experiment 1, only kidney manganese concentration was significantly affected by diet and was highest in soy-fed animals. In Experiment 2, plasma, kidney, and liver manganese were all significantly affected by diet and were highest in soy-fed animals and lowest in beef-fed animals.