Fluoride, calcium and phosphorus metabolism in the rat: Comparison of 'natural ingredient' with semipurified diets

Three groups of weanling female rats were fed different, commercially available, 'natural ingredient' diets containing 12, 28 or 45 parts/10⁶ F, mainly as bone meal, for six weeks. Two other groups were fed a low-fluoride (0.76 parts/10⁶) semipurified diet. They received fluoride doses, either in the drinking water or by daily intraperitoneal injection, which were approximately equal to the average dose of the other three groups. Rats on the 'natural ingredient' diets ingested more food and water and excreted more faeces arid urine, effects which were attributed to the higher amounts of dietary fibre, Na, K and Cl. Thus, at any given concentration of fluoride in the food or water, the level of fluoride ingestion and the ensuing effects would be influenced by the type of diet used. The values for fractional fluoride absorption (45-49%) and retention (38-47%) were similar among the groups given 'natural ingredient' diets. In the groups given semipurified diet, the corresponding values were about twice as high with the exception that fractional absorption was negative (-41%) in the injected group, which indicated net intestinal secretion of fluoride. Fluoride balances and tissue concentrations were highest in the groups fed the semipurified diet, even though the level of intake was not always higher. The fractional values for calcium and phosphorus absorption (41-51%) and retention (33-43%) were also similar among the groups given 'natural ingredient' diets. The corresponding values were about twice as high in the groups fed the semipurified diet. In terms of supporting maximum bone calcification, phosphorus absorption was marginal in two of the groups on the 'natural ingredient' diets. Because of their variable fluoride concentrations and ill-defined compositions, the use of 'natural ingredient' diets in research should be avoided.