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


METHODS
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 approximately 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 ( +/- SD) to 0.59 +/- 0.05 and 0.66 +/- 0.04 with increasing fat intake, whereas the molar ratio of chenodeoxycholate 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.
Bisschop
Peter H
PH
Department of Endocrinology & Metabolism, Academic Medical Center, University of Amsterdam, Netherlands. p.h.bishop@amc.uva.nl
Bandsma
Robert H J
RH
Stellaard
Frans
F
ter Harmsel
Anke
A
Meijer
Alfred J
AJ
Sauerwein
Hans P
HP
Kuipers
Folkert
F
Romijn
Johannes A
JA
D000328:Adult; D001647:Bile Acids and Salts / Q000096:biosynthesis* / Q000378:metabolism; D002784:Cholesterol / Q000097:blood*; D004032:Diet; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000494:pharmacology*; D004041:Dietary Fats / Q000008:administration & dosage / Q000494:pharmacology*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008297:Male; D008875:Middle Aged
D001647:Bile Acids and Salts; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D002784:Cholesterol