Lactate, Fructose and Glucose Oxidation Profiles in Sports Drinks and the Effect on Exercise Performance
Fructose and Glucose Oxidation Profiles in Sports Drinks and the
Effect on Exercise Performance. PLoS ONE 2(9): e927. doi:10.1371/journal.pone.0000927
Lactate, Fructose and Glucose Oxidation Profiles in Sports Drinks and the Effect on Exercise Performance
John L. Azevedo Jr. 0 1
Emily Tietz 0 1
Tashena Two-Feathers 0 1
Jeff Paull 0 1
Kenneth Chapman 0 1
0 Academic Editor: Chenxi Wang, University of Louisville , United States of America
1 Exercise Biology Laboratory, Department of Kinesiology, California State University Chico , Chico, California , United States of America
Exogenous carbohydrate oxidation was assessed in 6 male Category 1 and 2 cyclists who consumed CytoMaxTM (C) or a leading sports drink (G) before and during continuous exercise (CE). C contained lactate-polymer, fructose, glucose and glucose polymer, while G contained fructose and glucose. Peak power output and VO2 on a cycle ergometer were 408613 W and 67.463.2 mlO2?kg21?min21. Subjects performed 3 bouts of CE with C, and 2 with G at 62% VO2peak for 90 min, followed by high intensity (HI) exercise (86% VO2peak) to volitional fatigue. Subjects consumed 250 ml fluid immediately before (22 min) and every 15 min of cycling. Drinks at 22 and 45 min contained 100 mg of [U-13C]-lactate, -glucose or -fructose. Blood, pulmonary gas samples and 13CO2 excretion were taken prior to fluid ingestion and at 5,10,15,30,45,60,75, and 90 min of CE, at the end of HI, and 15 min of recovery. HI after CE was 25% longer with C than G (6.560.8 vs. 5.261.0 min, P,0.05). 13CO2 from the 22 min lactate tracer was significantly elevated above rest at 5 min of exercise, and peaked at 15 min. 13CO2 from the 22 min glucose tracer peaked at 45 min for C and G. 13CO2 increased rapidly from the 45 min lactate dose, and by 60 min of exercise was 33% greater than glucose in C or G, and 36% greater than fructose in G. 13CO2 production following tracer fructose ingestion was greater than glucose in the first 45 minutes in C and G. Cumulative recoveries of tracer during exercise were: 92%65.3% for lactate in C and 2564.0% for glucose in C or G. Recoveries for fructose in C and G were 7565.9% and 2666.6%, respectively. Lactate was used more rapidly and to a greater extent than fructose or glucose. CytoMax significantly enhanced HI.
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INTRODUCTION
Intense endurance exercise promotes dehydration and depletion of
blood glucose, muscle and liver glycogen, and electrolytes.
Endurance athletes must satisfy the needs for fluids, energy, and
electrolytes for optimal performance. Fluid-energy-electrolyte
replacement beverages (i.e., sports drinks) improve endurance
because they satisfy these needs, particularly in hot and humid
environments [1,2,3].
Traditional sports drinks supply energy in the form of sugars
(glucose, fructose, sucrose) and glucose polymers [1].
Carbohydrate is the main energy source for prolonged physical activity [4],
and of the dietary energy substrates, carbohydrates are most
readily digested and absorbed. The drinks also contain electrolytes
to replace those lost in sweat. Electrolytes also stimulate thirst,
promote solute absorption in the gastrointestinal (GI) tract [1,2,3],
and buffer endogenous acids [5].
A sports drink containing a 6% (w/v) glucose solution is
efficacious for promoting GI emptying and exercise performance.
Consumption of 1 liter per hour in 250 ml aliquots delivers 1 g/
min of glucose, which enhances fuel availability and provides other
benefits [1,3]. More, recently investigators [610] have
experimented with combinations of hexoses (e.g., 2 glucose/fructose) to
raise drink solute content above 6% by taking advantage of specific
intestinal transporters that promote solute absorption [1114].
The same investigators have used isotopically labeled solutes to
track the oxidation of specific energy substrates in sports drinks.
The results support the concept of increasing energy delivery by
expanding the metabolite delivery profile of the beverages.
Lactate is a dynamic substrate with great potential as an energy
source in sports drinks. To date, however, the efficacy of adding
lactate to these drinks has been sparsely assessed [5,15,16]. Lactate
was once considered a metabolic waste but is now recognized as an
important energy substrate in the body. Lactate is the main
product of carbohydrate metabolism and can be used as a fuel in
working muscle cells shuttled to other tissues such as the heart
where lactate is fuel [17], or to the liver were lactate serves as
a gluconeogenic precursor [18].
Lactate is transported across cell plasma and mitochondrial
membranes by a family of proton-lactate anion-coupled symporter
proteins [19,20,21], of which MCT1 is the predominant isoform in
muscle [22,23]. Related, but from a different gene family is the
sodium-coupled intestinal lactate transporter, sMCT, also known
as the slc5a8 [24,25]. The presence of monocarboxylate (i.e.,
lactate) transport proteins in the GI tract, erythrocytes, myocytes,
cardi (...truncated)