NUTRITION AND BILE FORMATION

This review summarizes current knowledge on mechanisms involved in hep atic bile formation and the role of diet as a modulator of this import ant liver function. It also includes cholestasis and nutritional inter ventions known to exert a beneficial effect in this pathology. Two com ponents of the bile flow have been described: bile acid dependent (BAD F) and bile acid independent (BAIF) flows and, several cellular struct ures are known to be involved in their generation. The membrane's enzy me activities, transporters and pumps play a particularly important ro le in bile secretion. Of the macronutrients, dietary protein has been shown to markedly affect bile flow. Protein deficient diet results in a decrease of both BADF and BAIDF, and in increased susceptibility to bile acid (BA)-induced cholestasis. Amino acid mixtures included in TP N solutions as well as certain individual amino acids can induce chole stasis mainly through alterations of plasma membrane composition and f unction. Supplementation with taurine and S-adenosyl methionine preven ts these forms of cholestasis by maintaining membrane integrity and fu nction. The quantity and quality of dietary lipid influences bile secr etion. Enhanced bile flow was observed with high polyunsaturated fat i ntake and was attributed to both higher BADF and BAIDF. Diets enriched in fish oil were found to result in the generation of greater bile fl ow when compared to diets enriched in corn oil. Dietary phospholipid ( soybean lecithin) supplementation increases bile secretion and exerts a beneficial effect against BA-induced cholestasis probably by mainten ance of membrane integrity. Although there is much information on the role of dietary carbohydrates, fibers, minerals and vitamins on choles terol and BA metabolism, relatively little is known about their implic ation in bile formation. Finally certain dietary strategies such as en ergy restriction and starve-refeed regimen can enhance bile secretion by their effects on BADF and BAIDF through maintenance of membrane fun ction. In conclusion, diet is an important modulator of bile formation and secretion by affecting BA synthesis and metabolism as well as mem brane structure and function.