Liver adaptations may be critical for regular exercise and high aerobic capacity to protect against metabolic disease, but mechanisms remain unknown. Bile acids (BAs) synthesized in the liver are bioactive and can putatively modify energy metabolism. Regular exercise influences BA metabolism in rodents but effects in humans are unknown.
This study tested if female subjects screened for high aerobic capacity (Hi-Fit, n=19) (VO2peak≥45 mL/kg/min) have increased hepatic BA synthesis and different circulating BA composition compared to those matched for age and body mass with low aerobic capacity (Lo-Fit, n=19) (VO2peak≤35 mL/kg/min). Diet patterns, activity level, stool, and blood were collected at baseline before receiving a 1-week standardized, eucaloric diet.
After the 1-week standardized diet, stool and blood were again collected, and an Oral Glucose Tolerance Test (OGTT) was performed to assess insulin sensitivity and postprandial BA response. Contrary to our hypothesis, serum 7α-hydroxy-4-cholesten-3-one (C4), a surrogate of BA synthesis was not different between groups while Hi-Fit women had lower fecal BA concentrations compared to Lo-Fit. However, Lo-Fit women had a higher and more sustained rise in circulating conjugated BAs during the OGTT. Hi-Fit women showed a significant post-OGTT elevation of the secondary BA, lithocholic acid (LCA), a potent TGR5 agonist, in contrast to Lo-Fit where no response was observed. A one-week control diet eliminated most differences in circulating BA species between groups.
Overall, the results emphasize the importance of using a standardized diet when evaluating BAs and indicate that regular exercise and aerobic capacity modulate BA metabolism under postprandial conditions.
