Glucose polymer molecular weight does not affect exogenous carbohydrate oxidation.
OBJECTIVE
To compare the effects of high (HMW) versus low molecular weight (LMW) glucose polymer solutions on the pattern of substrate oxidation during exercise.


METHODS
Eight cyclists (VO(2max): 63 +/- 8 mL.kg(-1).min(-1)) performed three 150-min cycling trials at 64 +/- 5% VO(2max) while ingesting 11.25% HMW (500-750 kg.mol(-1), 21 mOsm.kg(-1)) or LMW (8 kg.mol(-1), 110 mOsm.kg(-1)) solutions providing 1.8 g of carbohydrate per minute, or plain water. Substrate oxidation was determined using stable-isotope methods and indirect calorimetry.


RESULTS
Exogenous carbohydrate oxidation rate was not affected by carbohydrate molecular weight (P = 0.89, peak rate: 0.93 x// 1.37 g.min(-1)). There was no effect of carbohydrate molecular weight on endogenous carbohydrate or fat oxidation rates (P = 0.30), plasma free fatty acid (P = 0.14), lactate (P = 0.38), or glucose concentrations (P = 0.98), nor were there any serious gastrointestinal complaints reported for either of the two solutions during exercise.


CONCLUSIONS
Despite previous reports of faster gastric emptying and glycogen resynthesis suggesting enhanced glucose delivery, a markedly hypotonic HMW glucose polymer solution had no effect on exogenous and endogenous substrate oxidation rates during exercise, relative to a LMW glucose polymer solution. These data are consistent with there being no effect of carbohydrate structure or solution osmolality or viscosity on exogenous glucose oxidation and that ingested glucose polymers can only be oxidized on average up to 1.0 g.min during exercise.
Rowlands
David S
DS
Institute of Food, Nutrition, and Human Health, Massey University, Wellington, New Zealand. d.s.rowlands@massey.ac.nz
Wallis
Gareth A
GA
Shaw
Chris
C
Jentjens
Roy L P G
RL
Jeukendrup
Asker E
AE
D000328:Adult; D001628:Beverages; D001642:Bicycling / Q000502:physiology; D001944:Breath Tests; D004040:Dietary Carbohydrates / Q000009:adverse effects / Q000378:metabolism*; D004041:Dietary Fats / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005767:Gastrointestinal Diseases / Q000209:etiology; D005936:Glucans / Q000009:adverse effects / Q000737:chemistry*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008320:Maltose / Q000378:metabolism; D008970:Molecular Weight; D009994:Osmolar Concentration; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000502:physiology; D011134:Polysaccharides / Q000378:metabolism; D013177:Sports / Q000502:physiology*
D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005230:Fatty Acids, Nonesterified; D005936:Glucans; D011134:Polysaccharides; D019344:Lactic Acid; D008320:Maltose; C008315:maltodextrin; D005947:Glucose