Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration

Abstract

. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol Endocrinol Metab 290: E380 -E388, 2006. First published September 27, 2005 doi:10.1152/ajpendo.00268.2005.-Five days of a high-fat diet while training, followed by 1 day of carbohydrate (CHO) restoration, increases rates of whole body fat oxidation and decreases CHO oxidation during aerobic cycling. The mechanisms responsible for these shifts in fuel oxidation are unknown but involve up-and downregulation of key regulatory enzymes in the pathways of skeletal muscle fat and CHO metabolism, respectively. This study measured muscle PDH and HSL activities before and after 20 min of cycling at 70% V O2 peak and 1 min of sprinting at 150% peak power output (PPO). Estimations of muscle glycogenolysis were made during the initial minute of exercise at 70% V O2 peak and during the 1-min sprint. Seven male cyclists undertook this exercise protocol on two occasions. For 5 days, subjects consumed in random order either a high-CHO (HCHO) diet (10.3 g⅐kg Ϫ1 ⅐day Ϫ1 CHO, or ϳ70% of total energy intake) or an isoenergetic high-fat (FAT-adapt) diet (4.6 g⅐kg Ϫ1 ⅐day Ϫ1 FAT, or 67% of total energy) while undertaking supervised aerobic endurance training. On day 6 for both treatments, subjects ingested an HCHO diet and rested before their experimental trials on day 7. This CHO restoration resulted in similar resting glycogen contents (FAT-adapt 873 Ϯ 121 vs. HCHO 868 Ϯ 120 mol glucosyl units/g dry wt). However, the respiratory exchange ratio was lower during cycling at 70% V O2 peak in the FAT-adapt trial, which resulted in an ϳ45% increase and an ϳ30% decrease in fat and CHO oxidation, respectively. PDH activity was lower at rest and throughout exercise at 70% V O2 peak (1.69 Ϯ 0.25 vs. 2.39 Ϯ 0.19 mmol⅐kg wet wt Ϫ1 ⅐min Ϫ1) and the 1-min sprint in the FAT-adapt vs. the HCHO trial. Estimates of glycogenolysis during the 1st min of exercise at 70% V O2 peak and the 1-min sprint were also lower after FAT-adapt (9.1 Ϯ 1.1 vs. 13.4 Ϯ 2.1 and 37.3 Ϯ 5.1 vs. 50.5 Ϯ 2.7 glucosyl units⅐kg dry wt Ϫ1 ⅐min Ϫ1). HSL activity was ϳ20% higher (P ϭ 0.12) during exercise at 70% V O2 peak after FAT-adapt. Results indicate that previously reported decreases in whole body CHO oxidation and increases in fat oxidation after the FAT-adapt protocol are a function of metabolic changes within skeletal muscle. The metabolic signals responsible for the shift in muscle substrate use during cycling at 70% V O2 peak remain unclear, but lower accumulation of free ADP and AMP after the FAT-adapt trial may be responsible for the decreased glycogenolysis and PDH activation during sprinting. skeletal muscle metabolism; pyruvate dehydrogenase; substrate phosphorylation; fat oxidation; carbohydrate oxidation THERE HAS BEEN MUCH INTEREST in the metabolic adaptations that occur in skeletal muscle following a high-fat diet to increase rates of whole body fat oxidation and decrease rates of carbohydrate (CHO) oxidation. It is well establish...

High-fat diet overrules the effects of training on fiber-specific intramyocellular lipid utilization during exercise

“…By analogy, elevated IMCL hydrolysis during exercise in females compared with males probably also is largely driven by higher basal IMCL content (54,60). Such interpretation is also supported by the observation that 5 days of a HFD were sufficient to enhance HSL activity during moderate-intensity exercise by ϳ20 -30% (58). The precise role of IMCL concentration in regulating HSL activity is at present unknown.…”

“…By analogy, fatty acid infusion elevates the input of free fatty acids (FFAs) in the energy substrate mix fueling muscle contractions (22, 48a, 49). Furthermore, chronic exposure to a high-fat diet (HFD) also enhances the use of FFAs in endurance exercise (8,9,25,29,(32)(33)(34)58). This is, at least partly, due to upregulation of rate-limiting steps in fat metabolic pathways.…”

“…This is, at least partly, due to upregulation of rate-limiting steps in fat metabolic pathways. Thus FFA oxidation can be stimulated with appropriate chronic exercise and/or nutrition (e.g., HFD), which upregulates pivotal steps in FFA catabolism such as fatty acid translocase (FAT)/CD36 (4,9), ␤-hydroxyacyl CoA dehydrogenase (␤-HAD) (9,31), and hormone-sensitive lipase (HSL) (58). However, it is still unclear whether these adaptations are specifically due to the increased FFA supply per se or result from decreased glucose availability.…”

New strategies in sport nutrition to increase exercise performance

“…Although the overall result was a (non-significant) benefit of ~ 3 min in the control trial, the striking outcome was the observation that the cyclist's ability to exercise at higher intensities was impaired following the fat-adaptation strategy. A separate investigation completed around the same time provided the unifying mechanistic explanation of all the previous literature: chronic intake of the LCHF diet specifically impairs rather than spares glycogen utilisation during exercise by reducing glycogenolysis and reducing the active form of pyruvate dehydrogenase (PDHa) to down-regulate the entry of carbohydrate into the citric acid cycle [78]. This finding elicited the opinion that the LCHF had little role to play in the preparation of competitive athletes since it would likely impair their capacity for the high-intensity exercise that is a pre-requisite for success in the majority of conventional sports [79].…”

Carbohydrates for training and competition

“…is associated with an increased ability to oxidize fat during exercise and a decreased reliance on muscle glycogen utilization (Helge, Watt, Richter, Rennie, & Kiens, 2001;, there are also indications that it can reduce the chronic adaptations to training (Helge, Richter, & Kiens, 1996) and impair carbohydrate utilization (Stellingwerff et al, 2006) and the ability to sustain high-intensity exercise performance (Havemann et al, 2006). Therefore, the more recent train low protocols have utilized a different approach to reducing carbohydrate availability for training.…”