The effect of dietary fat on the turnover of cholic acid and on the composition of the biliary bile acids in man.

Because of the strong influence of dietary fat on serum cholesterol levels, there has been a great deal of interest in possible parallel effects on bile acid formation and excretion. The output of bile acids in human feces has been determined in several studies by a variety of chemical and isotopic procedures. Values have been reported ranging from less than 0.1 to as high as 2 g per day (1-9). In several of these studies, the inclusion of unsaturated fat in the diet has been found to cause an increase in the total bile acid output, which might account for the concomitant decrease in serum cholesterol level (1-4). On the other hand, in other studies, no such effect of unsaturated fat on the total bile acid output was observed (8, 10-13). Direct analysis of fecal end products is beset with serious technical problems, making it difficult to obtain valid quantitative results (14). The bile acids produced in the liver (cholic acid and chenodeoxycholic acid) are radically modified by bacterial action in the intestine, giving rise to an extremely complex, heterogeneous mixture of products (15, 16). If changes in the diet alter the relative abundance of the several fecal bile acids, then an analysis limited to only one or a few components could give an incomplete and erroneous impression of the changes induced in total bile acid excretion. Lindstedt (17) has previously reported an isotopic method for determination of cholic acid turnover in man based on serial measurements of the