Low-fat, high-carbohydrate and high-fat, low-carbohydrate diets decrease primary bile acid synthesis in humans

Abstract

Background: Dietary fat content influences bile salt metabolism, but quantitative data from controlled studies in humans are scarce. Objective: The objective of the study was to establish the effect of dietary fat content on the metabolism of primary bile salts. Design: The effects of eucaloric extremely low-fat (0%), intermediate-fat (41%; control diet), and extremely high-fat (83%) diets on kinetic values of cholate and chenodeoxycholate metabolism were determined after 11 d by using stable isotope dilution in 6 healthy men. All diets contained identical amounts of cholesterol. Results: The total primary bile salt pool size was not significantly affected by dietary fat content, although the chenodeoxycholate pool was significantly higher during the low-fat diet. Fractional turnover rates of both primary bile salts were 30-50% lower during the low-and high-fat diets than during the control diet. Total hepatic bile salt synthesis was ≈30% lower during both the high- and low-fat diets, but synthesis rates of the 2 primary bile salts were differentially affected. The molar ratio of cholate to total bile salt synthesis increased from 0.50 ± 0.05 (x̄ ± SD) to 0.59 ± 0.05 and 0.66 ± 0.04 with increasing fat intake, whereas the molar ratio of chenodeoxy-cholate to total bile salt synthesis decreased from 0.50 ± 0.05 to 0.41 ± 0.05 and 0.34 ± 0.04. The relative concentration of deoxycholate in plasma increased during the low-fat period, which indicated increased absorption from the colon. Conclusions: Both low- and high-fat diets reduce the synthesis and turnover rates of primary bile salts in humans, although probably through different mechanisms, and consequently they affect the removal of cholesterol from the body. © 2004 American Society for Clinical Nutrition.