Effect of high and low glycaemic index recovery diets on intramuscular lipid oxidation during aerobic exercise

Abstract

Intramyocellular lipid (IMCL) and plasma NEFA are important skeletal muscle fuel sources. By raising blood insulin concentrations, carbohydrate ingestion inhibits lypolysis and reduces circulating NEFA. We hypothesised that differences in the postprandial glycaemic and insulin response to carbohydrates (i.e. glycaemic index; GI) could alter NEFA availability and IMCL use during subsequent exercise. Endurance-trained individuals (n 7) cycled for 90 min at 70 % V O 2peak and then consumed either high GI (HGI) or low GI (LGI) meals over the following 12 h. The following day after an overnight fast, the 90 min cycle was repeated. IMCL content of the vastus lateralis was quantified using magnetic resonance spectroscopy before and after exercise. Blood samples were collected at 15 min intervals throughout exercise and analysed for NEFA, glycerol, glucose, insulin, and lactate. Substrate oxidation was calculated from expired air samples. The 90 min cycle resulted in .2-fold greater reduction in IMCL in the HGI trial (3·5 (SEM 1·0) mM/kg wet weight) than the LGI trial (1·6 (SEM 0·3) mM/kg wet weight, P, 0·05). During exercise, NEFA availability was reduced in the HGI trial compared to the LGI trial (area under curve 2·36 (SEM 0·14) mEq/l per h v. 3·14 (SEM 0·28) mEq/l per h, P,0·05 respectively). No other differences were significant. The findings suggest that HGI carbohydrates reduce NEFA availability during exercise and increase reliance on IMCL as a substrate source during moderate intensity exercise.Glycaemic index: Intramyocellular lipid: Magnetic resonance spectroscopy: Exercise: Skeletal muscle During moderate intensity exercise, the energy for ATP homeostasis in skeletal muscle is primarily obtained from the oxidation of glycogen and lipid. Glycogen plays a pivotal role in producing energy and preventing the development of muscle fatigue in submaximal exercise 1 -4 . Intramuscular lipid levels are also readily oxidised during prolonged exercise 5 -7 and are elevated in endurance-trained individuals 8 . The rate of substrate oxidation, whether glycogen or lipid, is influenced by both existing pre-exercise substrate within the muscle 9 , and circulating substrate availability during exercise 10 -13 . Although considerable work has been undertaken on optimising glycogen storage with diet, less is known about the relative influence of diet upon both glycogen and lipid oxidation.High levels of carbohydrate intake have been shown to improve glycogen repletion after exercise 14,15 . An early study also reported that consuming carbohydrates which are rapidly absorbed into the circulatory system, termed high glycaemic index (HGI) carbohydrates, optimised the storage of plasma glucose as skeletal muscle glycogen following glycogen-depleting exercise 16 . It has also been reported that the postprandial hyperinsulinaemia accompanying high carbohydrate intake reduces the rate of fat oxidation 17 -19 , increasing reliance upon glycogen oxidation during exercise. Although high postprandial levels of insulin may increas...

Dietary glycemic index influences lipid oxidation but not muscle or liver glycogen oxidation during exercise

“…The effect has been observed immediately after a high-GI meal (7,9,25,28,37,38,41) and on the following day (26,29). The present findings suggest that, when NEFA availability is compromised, there is a twofold increase in reliance on IMCL as a fuel source during exercise.…”

“…All spectra were analyzed using "java-based magnetic resonance user interface" software (jMRUI version 3.0) (18,19) and AMARES fitting routine (32). IMCL concentrations were calculated as previously described (29). Quantitation of 13 C spectra was performed by comparison of in vivo [ 1 C]glycogen 13 C signal amplitudes with that of a standard glycogen solution (100 mM glycogen, 70 mM KCl, 0.05% sodium azide).…”

“…In line with this, studies have shown that carbohydrates, which are rapidly absorbed in the circulation and produce a large insulin response [termed high glycemic index (GI)] optimize the rate of glycogen resynthesis (31) and storage (2) after exercise. Conversely, we have recently demonstrated that short-term feeding of mixed meals differing by GI alone influence both lipid availability and oxidation (29). A high-GI diet reduces NEFA availability and increases reliance on intramuscular lipid oxidation during exercise.…”

Glycemic Index and Endurance Performance

“…Furthermore, two recent studies carried out in endurance-trained participants have reported that consuming HGI meals during 24 hr of recovery leads to greater utilization of IMTG and reduced availability of nonesterified fatty acids during subsequent exercise (performed in a fasted state) than consuming LGI recovery meals (Stevenson et al, 2009b;Trenell, Stevenson, Stockmann, & Brand-Miller, 2007). These results suggest that consuming an LGI diet between bouts of prolonged strenuous exercise reduces dependence on intramuscular lipid stores and increases the use of circulating plasma FFAs derived from other fat stores (Stevenson, Thelwall, et al, 2009;Trenell, Stevenson, Stockmann, & Brand-Miller, 2007), thus explaining the increased fat oxidation and endurance capacity observed by Stevenson , Williams, McComb, and Oram (2005).…”

“…Consuming adequate CHO for muscle glycogen synthesis is still important, although some protein may be substituted for CHO without a decline in muscle glycogen synthesis and a probable enhancement of muscle protein synthesis (Jentjens & Jeukendrup, 2003). However, the consumption of LGI CHO during 24 hr of recovery results in a sparing of IMCL and an increased rate of fat oxidation when subsequent exercise is performed in a fasted state, suggesting a potential tradeoff between the increased insulin secretion needed for muscle glycogen synthesis and the decreased insulin secretion needed for nonesterified fatty acid availability during subsequent exercise (Stevenson, Thelwall, et al, 2009;Trenell et al, 2007).…”