EAL

NAP: Competition (2007)

Citation:

Burke LM, Claassen A, Hawley JA, and Noakes TD. Carbohydrate intake during prolonged cycling minimizes effect of glycemic index of preexercise meal. Journal of Applied Physiology, 1998; 85: 2,220-2,226.

PubMed ID: 9843546

Study Design:

Randomized crossover trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

The purpose of this investigation was to examine whether the GI of pre-exercise CHO intake has any impact on exercise metabolism and subsequent performance when large amounts of CHO are consumed during the exercise session.

Inclusion Criteria:

Endurance-trained cyclists.

Exclusion Criteria:

Exclusion criteria was not noted.

Description of Study Protocol:

Recruitment: Male volunteers
Design: Randomized crossover trial; three trials in a randomized counter-balanced order, with each trial separated by a period of seven days
Blinding used: The only blinding used was that subjects were kept blind to time.

Intervention

Each subject underwent three trials separated by a period of seven days
On each occasion, a test meal was consumed two hours before cycling at 70% VO₂ _max.
- HGI CHO-rich meal (HGI trial) of potato
- LGI CHO-rich meal of lightly cooked pasta
- Control meal (Con trial) of low-energy jelly
- All CHO-rich meals contained 2g CHO per kg
Subjects rode for two hours at 70% of VO₂ max. Every 20 minutes, they ingested a CHO drink providing 24ml per kg and 2.4g of CHO per kg.
Subjects were given one minute to rest after the steady-state ride and then performed a performance test, which consisted of the time to complete 300kJ.

Statistical Analysis

Two-factor (diet and time) ANOVA with repeated measures
CHO oxidation and time trial performances were compared by using one-way ANOVA
P<0.05.

Data Collection Summary:

Timing of Measurements

Blood Draws: Fasting, 30, 60, 90 and 120 minutes post-prandial; every 20 minutes after the start of exercise.

Dependent Variables

Plasma glucose
Serum insulin
Serum FFA
RPE
Performance time.

Independent Variables

CHO meals (HGI, LGI or placebo).

Control Variables

Exercise conditions
Exercise and intake 24 hours before exercise.

Description of Actual Data Sample:

Initial N: Six males
Attrition (final N): Six males
Age: 22.8±2.3 years
Ethnicity: Not noted.

Anthropometrics

Weight: 72.0±4.1kg
VO_{2 max}: 68.6±3.8ml per kg per min.

Location

South Africa.

Summary of Results:

Other Findings

Despite differences in pre-exercise glucose, insulin and FFA concentrations among trials, both total CHO oxidation during steady-state exercise (403±16g over two hours for high-GI; 376±29g over two hours for low-GI; 373±24g over two hours for control) and oxidation of the ingested carbohydrate (65±6g over two hours for high-GI; 57±6g over two hours for low-GI; 63±5g over two hours for control) were similar
There was no difference in time required to complete the subsequent performance ride (946±23 seconds for high-GI; 953±36 seconds for low-GI; 970±26 seconds for control trials)
Subjects' RPE rose steadily through steady-state exercise and did not differ among trials.

Author Conclusion:

The major finding of this investigation was that when large amounts (approximately 170g) of carbohydrates were ingested during prolonged cycling (approximately 2.5 hours), there were minimal differences in the metabolic and performance responses to the choice of pre-event meal
We conclude that the ingestion of carbohydrates during prolonged moderate-intensity cycling, according to current sports nutrition guidelines, minimizes any differences in the metabolic and performance responses arising from the choice of pre-event meal
Contrary to some advice that low-glycemic index carbohydrate-rich foods are the preferred exercise choice, endurance athletes are guided that when significant amounts of carbohydrates are consumed during exercise, they may choose their pre-exercise meal strategies in accordance with their personal preferences and previous experience.

Funding Source:

Government:

Medical Research Council South Africa

Industry:

Potato Producers' Organization of South Africa

Commodity Group:

University/Hospital:

University of Cape Town

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

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

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?	No
	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?	N/A
	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?		???
	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?	No
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