EAL

NAP: Competition (2007)

Citation:

Febbraio MA, Chiu A, Angus DJ, Arkinstall MJ, Hawley JA. Effects of carbohydrate ingestion before and during exercise on glucose kinetics and performance. J Appl Physiol. 2000; 89: 2,220-2,226.

PubMed ID: 11090571

Study Design:

Randomized crossover trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To determine the effect of carbohydrate ingestion before, during or in combination on exercise metabolism and performance.

Inclusion Criteria:

Endurance-trained men.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not specified.
Design: Randomized crossover trial.
Blinding used: Double-blind.

Intervention

Subjects cycled for 120 minutes at 63% of peak power output, followed by a seven-kJ per kg body weight time trial.

On 4 separate occasions, subjects received either:

Placebo beverage before and every 15 minutes during exercise
Placebo 30 minutes before and two grams per kg of body weight of carbohydrate in a 6.4% carbohydrate solution during exercise
Two grams per kg body weight carbohydrate in 25.7% carbohydrate beverage 30 minutes before and a placebo during exercise
two grams per kg body weight carbohydrate in a 25.7% carbohydrate beverage 30 minutes before and two grams per kg body weight of carbohydrate in a 6.4% carbohydrate solution during exercise.

Statistical Analysis

Metabolic data from four trials were compared using a two-factor (time and treatment) ANOVA with repeated measures
A one-way ANOVA was used to compare time to complete the performance cycle
Newman-Keuls post-hoc tests were used to locate differences when ANOVA revealed a significant interaction.

Data Collection Summary:

Timing of Measurements

Heart rate, ratings of perceived exertion, VO₂, VCO₂ and respiratory exchange ratio were measured at 15-minute intervals during exercise. In addition to the basal blood sample, further samples were obtained at 10, 20 and 30 minutes post-prandial and at 20-minute intervals during exercise.

Dependent Variables

Heart rate measured by telemetry
RPE measured using a 19-point scale
VO₂, VCO₂ and RER measured using Douglas bag method
Blood analyzed for glucose, insulin, glycerol and FFA.

Independent Variables

Dietary intervention
- Placebo beverage before and during exercise
- Placebo 30 minutes before and two grams per kg body weight of carbohydrate in a 6.4% carbohydrate solution during exercise
- Two grams per kg body weight carbohydrate in 25.7% carbohydrate beverage 30 minutes before and a placebo during exercise
- Two grams per kg body weight carbohydrate in a 25.7% carbohydrate beverage 30 minutes before and two grams per kg body weight of carbohydrate in a 6.4% carbohydrate solution during exercise.
Subjects were fasting and had abstained from alcohol, caffeine, tobacco and strenuous exercise for the prior 24 hours
Subjects were provided with prepared food packages prior to trials.

Description of Actual Data Sample:

Initial N: Seven trained men
Attrition: Seven
Age: Mean age, 26.9±6.4 years
Ethnicity: Not mentioned
Location: Australia.

Summary of Results:

Other Findings

Mean VO₂, VCO₂, heart rate, RER and RPE were not different between trials
Ingestion of the carbohydrate beverage prior to exercise markedly (over eight mM) increased plasma glucose concentration compared with the placebo trials (five mM)
However, plasma glucose concentration fell rapidly at the onset of exercise so that after 80 minutes it was similar between all treatments (six mM)
After this time, plasma glucose concentration declined in both trials given placebo during exercise (P<0.05), but was well-maintained in the groups receiving carbohydrates during exercise
Ingestion of the carbohydrate beverage before exercise increased rates of glucose appearance and disappearance, compared with the placebo trials at the onset of and early during exercise (P<0.05)
However, late in exercise, both rates of glucose appearance and disappearance were higher in the trials receiving carbohydrates during exercise, compared with other trials (P<0.05)
Although calculated rates of glucose oxidation were different, when comparing the four trials (P<0.05), total carbohydrate oxidation and total fat oxidation were similar.
Despite this, time trial was improved in the trials with carbohydrate consumed during exercise than in placebo before and during exercise (P < 0.05).

Author Conclusion:

In summary, our data demonstrate that, even when carbohydrate is ingested in large quantities before and during exercise, the amount of glucose disappearance is relatively minor and the contribution of carbohydrates and fat to total substrate use were not affected, when compared with ingestion of a placebo
In addition, when equal amounts of carbohydrates were consumed either 30 minutes before or throughout exercise, endurance performance was increased only when carbohydrates were consumed throughout exercise, despite the fact that the contribution of glucose to energy turnover was higher when glucose was ingested before exercise
The maintenance of high-plasma glucose concentrations throughout exercise appears to increase exercise performance.

Funding Source:

Industry:

SmithKline Beecham Consumer Healthcare (UK)

Other:

University/Hospital:

University of Melbourne, Royal Melbourne Institute of Technology University

Reviewer Comments:

Inclusion and exclusion criteria and recruitment methods were not well-defined.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	Yes
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	Yes

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		???
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	No
	2.2.	Were criteria applied equally to all study groups?	???
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	???
3.	Were study groups comparable?		Yes
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	Yes
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	Yes
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	Yes
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	N/A
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	N/A
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	Yes
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	Yes
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	N/A
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		Yes
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	Yes
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	Yes
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	Yes
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	Yes
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	Yes
	6.6.	Were extra or unplanned treatments described?	Yes
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	Yes
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	Yes
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	Yes
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	Yes
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	Yes
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	N/A
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	N/A
	8.6.	Was clinical significance as well as statistical significance reported?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
9.	Are conclusions supported by results with biases and limitations taken into consideration?		Yes
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	Yes
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes