Mineral metabolism on rice diets.

Over half the population of the world eats a diet in which rice predominates and such a diet usually has a low mineral content. This is certainly true for the diets consumed by most of the people of Ceylon (Nicholls, 1936; Nicholls & Nimalasuriya, 1939; Bibile, Cullumbine, Watson & Wickramanayake, 1949; Cullumbine, ~gqga), and it is difficult to understand how these people can grow and maintain health on such low mineral intakes. The problem is further complicated by the fact that these diets, which are rich in cereals (50-60 7; at least of the total calories may be obtained from rice), have a relatively high content of phosphorus, and presumably of phytate phosphorus too. McCance & Widdowson (1942-3a) have shown that the phytic acid of bread interferes with the absorption from the gut of calcium and magnesium. Their results indicate that the greater the phytic-acid content of a diet rich in bread, that is, the higher the extraction rate of the flour from which the bread is made, the less is the absorption of these minerals from the intestine. Walker, Fox & Irving (1948) have confirmed these findings and they made the further interesting observation that subjects can adapt themselves to a lowered absorption of calcium or magnesium. This recalls the suggestion of Nicholls & Nimalasuriya (1939) who, when discussing the low dietary intake of calcium by the average Ceylonese, concluded that only a process of racial adaptation could explain the growth of Ceylonese without the occurrence of bony abnormalities. Unpolished rice has a higher phytic-acid content than polished rice (McCance & Widdowson, 1935), and both types of rice are consumed in Ceylon. I t seemed desirable, therefore, to determine whether there was any difference in the calcium and magnesium metabolism of subjects when eating diets first high in unpolished rice and then in polished rice. Further, it seemed necessary to see whether the suggestion of the occurrence of a process of adaptation has any experimental basis. I