The impact of carbohydrate ingestion on the regulation of fat oxidation following exercise

Abstract

Purpose: To determine the impact of carbohydrate (CHO)ingestion on the regulation of fat oxidation following glycogen lowering exercise. Methods: Six males (age 23.4 2 1.7y, vo2peak 58.0 2 2.1 ml.kg-'.min-') participated in the study. Subjects performed an incremental maximal cycle ergometer test and a verification trial to determine the workload corresponding to 75%V02peak. On separate days, subjects exercised at 75% vO2peak for 90 min. Following exercise, subjects consumed either a CHO drink or a flavoured placebo (PLA). Substrate oxidation was measured for I h after exercise using indirect calorimetry. Before, immediately after, and A h after exercise, subjects had a muscle biopsy taken from the vastus lateralis. Results: Subjects exercised at a similar %VO2peak during both the CHO (71.5 2 I -8% v02peak) and the PLA (72.5 2 1.8%VO2peak) trials. Energy expended during and following exercise was similar between trials. The contribution of fat towards energy expenditure (%EE) during recovery was lower in the CHO trial than in the placebo trial (p4.05). The opposite was true for carbohydrate (pc0.05). Exercise lowered muscle glycogen in both trials. Exercise decreased (pC0.05) serum insulin levels and increased (pc0.05) non-esterified fatty acid (NEFA) levels. CHO ingestion led to a dramatic increase in glucose and insulin levels and a drop in NEFA levels (p<0.05). The phosphorytataion of acety bCoA carboxylase (ACC), 5'AMP-activated protein klnase (AMPK) and hormone sensitive lipase (HSL) increased with exercise (p<0.05). ACC and AMPK phosphorylation in the CHO trial was lower at 1 h post than in the PLA trial (pc0.05). HSL phosphorylation remained above baseline at 1 h post in the PLA but not the CHO trial. Conclusion: Results indicate that CHO ingestion following exercise suppressed fat oxidation, possibly by relieving the phosphorylation duced inhibition of ACC, allowing for an increase in malonyl CoA levels