Bioavailability, mineral interference

The data presented in this paper indicate that excess levels (0.75%) of dietary zinc result in decreases in the bioavailability of calcium and phosphorus in rats and interfere with normal bone mineralization. High dietary levels of calcium or zinc appeared to cause a shift in the excretion of phosphorus from the urine to the feces, while the presence of extra phosphorus tended to keep the pathway of phosphorus excretion via the urine. The presence of large amounts of phosphorus in the Intestinal tract due to high intakes of zinc would increase the possibility of the formation of insoluble phosphate salts with various cations, including calcium, which may be present. A shift in phosphorus excretion from the feces to the urine, however, could result in an environmental condition within the system which would tend to increase the bioavailability of cations to the animal. The adverse effect of zinc toxicity on calcium and phosphorus status of young rats could be alleviated with calcium and/or phosphorus supplements. 

An increase in consumption of whole grain flour products is one of the nutritional aims in Norway. The high content of dietary fiber or factors associated with it, however, present in bran and whole grain flour, may interfere with the bioavailability of minerals as suggested by several authors ( , 7, 8),... 

However, tamarind seeds have low levels of phytic acid comparable that of lima bean (Egbe and Akinyele, 1990, cited in 4)). Phytic acid decreases bioavailability of certain minerals and may interfere with the ntihzation of proteins dne to the formation of phytate-protein and phytate-mineial-protein complexes and also inhibits the digestive enzymes (Reddy et al, 1982, cited in 4)). The phytate conld, however, be snbstantially eliminated by processing methods snch as soaking and antoclaving (Reddy et al, 1982, cited in 4)). 

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