Effect of prolonged exercise and pre-exercise dietary manipulation on hepatic triglycerides in trained men

The purpose of this study was to examine the effect of exercise and pre-exercise dietary manipulation on hepatic triglyceride concentration (HTGC). HTGC was measured by proton magnetic resonance spectroscopy ((1)H-MRS) before and after 90 min of moderate intensity cycling in six endurance trained males following 67 h of mixed diet (M) and an isocaloric minimal carbohydrate (2%) high fat (83%) diet (HF). Diets were administered by balanced crossover design. Whole-body fat oxidation, plasma-free fatty acid (FFA), glycerol and triglyceride concentrations were significantly elevated during exercise in HF versus M (P < 0.05 for all). There was no significant treatment × time interaction for HTGC (P = 0.368). However, there was a significant net increase in HTGC (time effect) during the combined 6 h exercise and post-exercise period (P = 0.037). In conclusion, we observed no measurable net change in the hepatic triglyceride pool across a period involving a prolonged exercise bout. Furthermore, manipulation of pre-exercise dietary intake did not influence the interaction between the hepatic triglyceride concentration and exercise in lean trained men. This supports the contention that hepatic triglycerides do not meaningfully contribute to the high rate of fat oxidation observed during acute exercise, or the enhancement of this with regular exercise training and/or pre-exercise dietary manipulation.