Influência de produtos alimentícios ricos em fibra na biodisponibilidade de cádmio e de metais essenciais

Abstract

Dietary fibers can interfere in the bioavailability of mineral elements both negatively and positively. This has been the subject of several researches because there is a great interest in essential minerals; also, some studies have been done regarding toxic elements such as cadmium (Cd). Environmental contamination with Cd and its consequent interference in the food chain can cause serious problems in humans and animals affecting several organs in general, and this can become even worse when exposure takes place during growth. Fiber-rich supplements are employed by people that have low levels of fiber in the diet. On the other hand, multimixtures (MMs) are low-cost food supplements with different compositions that are used to improve the nutritional conditions of children. These supplements are normally rich in fibers and mineral elements. The objective of this study was to evaluate the effect of MMs and other food products rich in dietary fibers on the absorption of mineral elements and on Cd absorption, accumulation, and toxicity in growing rats. Three independent experiments were conducted. In the first experiment, MMs, used as supplements at a 5% proportion in diets, increased apparent absolute absorption of phosphorus, magnesium and manganese, proportionally to its level of dietary fiber, but did not interfere in calcium or copper absorption. This suggests that these supplements can be a source of some minerals in the diet, and similar proportions to those employed in this study did not diminish calcium and copper absorption. In the second experiment, one MM, rich in fibers and essential minerals did not diminish either Cd accumulation or toxicity when this metal was employed at 25 mg/kg in the diet, but MM diminished Cd accumulation in the kidneys when it was employed at 5 mg/kg in the diet. This latter Cd level is similar to human exposure in some contaminated areas, which suggests that MM may contribute to diminish Cd toxicity in polluted areas. In the third experiment, when flaxseed and bran wheat were compared to purified cellulose, it was observed that flaxseed, which has a higher proportion of soluble fiber, increased Cd accumulation in the liver and kidneys of growing rats in comparison to the other two fiber sources, which have basically insoluble fiber. These results indicate that foods with a higher proportion of soluble fiber can increase Cd body retention, suggesting that one should be careful when ingesting these foods in Cd contaminated areas. Flaxseed and bran wheat, used as sources of dietary fiber for rats exposed do Cd, decreased apparent absorption of Ca and P and increased apparent absorption of Mg in comparison to purified cellulose, which might be attributed to an interaction of Cd and phytate present in these fiber sources. Results of the present study show that MMs can be source of some essential mineral, besides reducing renal Cd accumulation, after exposure to low Cd doses. It was also observed that different sources of fiber may differentially affect the retention of toxic metals like Cd, and one should be careful when using foodstuffs rich in soluble fiber, like flaxseed, which can increase Cd retention.