EAL

NAP: Competition (2007)

Citation:

Paul D, Jacobs KA, Geor RJ, Hinchcliff KW. No effect of preexercise meal on substrate metabolism and time trial performance during intense endurance exercise. Int J Sport Nutr Exerc Metab. 2003; 13 (4): 489-503.

PubMed ID: 14967872

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 compare the effects of a fat- and carbohydrate-rich meal three to four hours before exercise, with fasting on whole-body fat and CHO oxidation, muscle glycogen utilization and rates of appearance and disappearance of blood glucose during 30 minutes of cycling above lactate threshold in CHO-replete subjects
To determine if there is an effect of pre-exercise meal on 20-km time trial performance that followed the 30 minutes of exercise.

Inclusion Criteria:

Endurance-trained men, amateur competitive cyclists and triathletes who were training for competition or in the competitive phase of their season.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

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

Intervention

Subjects exercised for 30 minutes above lactate threshold, followed by a 20-km time trial
3.5 hours before exercise, subjects consumed a carbohydrate meal (three grams CHO per kg), an isoenergetic fat meal (1.3g fat per kg) or a placebo meal (no energy content) on three separate occasions in randomized order.

Statistical Analysis

Comparisons between the three trials over time were analyzed by two-way ANOVA with repeated measures
Tukey-Kramer HSD test used to locate specific differences between means.

Data Collection Summary:

Timing of Measurements

Gas exchange measured for the first and last five minutes of the 30-minute exercise session and for five minutes during the time trial
Heart rate measured continuously
Blood samples collected before isotope infusion and 30, 15 and zero minutes before the 30-minute exercise session, at 10, 20 and 30 minutes into the 30-minute exercise session and immediately before and after the time trial.

Dependent Variables

Blood samples analyzed for glucose, lactate, glucose enrichment, hematocrit, glycerol, FFA and insulin
Muscle biopsies taken from vastus lateralis
Gas exchange measurements made with Applied Electrochemistry analyzers
Heart rate monitored through telemetry.

Independent Variables

3.5 hours before exercise, subjects consumed a carbohydrate meal (three grams CHO per kg), an isoenergetic fat meal (1.3g fat per kg) or fasted
Prior to exercise testing, all subjects exercised for 30 minutes and received high-CHO dinner and breakfast to ensure that the subjects had replete stores of liver and muscle glycogen.

Description of Actual Data Sample:

Initial N: Eight men
Attrition (final N): Eight
Age: Not mentioned
Ethnicity: Not mentioned
Location: United States.

Summary of Results:

Fat Oxidation Rates

Time (Minutes)	Carbohydrate	Fat	Placebo
Zero to five	0±0	0±0	1.6±1.1, P<0.01
25 - 30	3.2±1.6	13.3±1.6, P<0.01	15.9±2.7, P<0.01
Time Trial	4.8±2.1	16.5±2.7, P<0.01	17.0±3.2, P<0.01

Other Findings

Treatments had no effect on CHO oxidation during exercise, but the carbohydrate meal decreased whole body fat oxidation during the last five minutes of the 30-minute exercise session and time trial, respectively (3.2±1.6 and 4.8±2.1micromol per kg per minute, P<0.05), when compared to the fat meal (13.3±1.6 and 16.5±2.7micromol per kg per minute) and placebo (15.9±2.7 and 17.0±3.2micromol per kg per minute)
Glucose rate of appearance and disappearance and muscle glycogen were not significantly different among treatments during exercise
Time trial performances were similar for carbohydrate, fat and placebo meals.

Author Conclusion:

In conclusion, the macronutrient composition of a meal prior to high-intensity endurance exercise elicits minor effects on whole-body fat oxidation and no effect on whole-body CHO oxidation, glucose kinetics or muscle glycogen use, when compared to a fast
In turn, there is no evidence to suggest that pre-exercise meal composition has any effect on subsequent 20-km time trial performance
Assuming that pre-exercise carbohydrate stores are not compromised, it appears as though a meal may not be necessary prior to intense exercise that lasts approximately one hour
It is likely that a pre-exercise meal alone cannot produce physiologically significant increases in plasma FFA unless it is followed by a heparin injection, which is not practical or ethical in athletic competition.

Funding Source:

Industry:

Gatorade Sport Science Center

Food Company:

University/Hospital:

Graduate School of Ohio State University

Reviewer Comments:

Inclusion criteria, exclusion criteria, recruitment methods and subjects were not well-described.

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?	No
	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?	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?		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