EAL

NAP: Competition (2007)

Citation:

Rowlands DS, Hopkins WG. Effect of high-fat, high-carbohydrate, and high-protein meals on metabolism and performance during endurance cycling. Int J Sport Nutr Exerc Metab. 2002; 12 (3): 318-335.

PubMed ID: 12432176

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 investigate the effect of pre-exercise meal composition on metabolism and performance.

Inclusion Criteria:

Competitive cyclists and triathletes.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

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

Intervention

For five weeks, subjects ingested either an isoenergetic high-fat (10% protein, 5% carbohydrate, 85% fat), high-carbohydrate (10% protein, 85% carbohydrate, 5% fat) or high-protein meal (30% protein, 40% carbohydrate, 30% fat) 90 minutes before a weekly exercise test
The test consisted of a one-hour pre-load at 55% peak power, five 10-minute incremental loads from 55% to 82% peak power and a 50km time trial that included three one-kilometer and four-kilometer sprints
A carbohydrate supplement (6% carbohydrate) was ingested throughout the exercise.

Statistical Analysis

The effects of the meals on metabolic and performance variables were estimated using a repeated measured analysis
Measures of centrality and spread are means and SD
Most outcome variables were log-transformed
Performance and metabolic data are shown as least squares means
Reliability of sprint and 50-kilometer time is expressed as the within-subject error derived from the repeated measures analysis.

Data Collection Summary:

Timing of Measurements

Gas exchange was measured before exercise and then continuously
Blood samples were drawn at five minutes before the meal, approximately 30 and approximately 75 minutes after the meal, at 30 and 60 minutes of the one-hour pre-load, upon completion of the incremental loads and at the end of the time trial.

Dependent Variables

Gas exchange was measured through an online gas analysis system
Blood samples were analyzed for glucagon, insulin, FFA, glycerol and glucose.

Independent Variables

Subjects ingested either a high-fat, high-carbohydrate or high-protein meal 90 minutes before a weekly exercise test for five weeks
Subjects completed a four-day dietary and one-week training diary during the week before the familiarization test and then repeated the normal weekly diet and training regimens throughout four weeks of the study.

Description of Actual Data Sample:

Initial N: 12 cyclists, all male
Attrition (final N): 12
Age: Mean, 27±8 years
Ethnicity: Not mentioned
Location: New Zealand.

Summary of Results:

Other Findings

There was no clear effect of meal composition on performance
Relative to the high-protein and high-fat meals, the high-carbohydrate meal raised RER by 0.03 to 0.05, halved the peak fat oxidation rate and reduced the fat oxidation across all workloads by a factor of 0.20 to 0.58 (P=0.002-0.0001)
Reduced fat availability may have accounted for this reduction, as indicated by lower plasma fatty acid, lower glycerol and higher pre-exercise insulin concentrations, relative to the other meals (P=0.04-0.0001)
In contrast, fat oxidation following the high-protein meal was similar to that following the high-fat meal. This similarity was linked to evidence suggesting greater lipolysis and plasma fat availability, following high-protein relative to high-carbohydrate meals.

Author Conclusion:

In conclusion, the high-carbohydrate meal given 90 minutes before exercise elevated pre-exercise plasma-insulin concentration and suppressed fat oxidation during exercise, relative to the high-fat and high-protein meals. In contrast, fat oxidation following the high-protein and the high-fat meals was similar to that of fasting, probably because of more fat in circulation relative to that following the high-carbohydrate meal.
In the high-protein meal condition, the elevated fat availability could be mediated by a metabolic effect associated with the higher protein content of the meal
Despite the effects of these meals on metabolism, there was no clear effect on performance.

Funding Source:

Reviewer Comments:

Inclusion criteria, exclusion criteria and recruitment methods were not well-defined
Authors note that the ingestion of the CHO supplement during exercise may have minimized any potential difference in metabolic and performance responses to the pre-exercise meal
Muscle glycogen was not measured.

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?		???
	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?	???
	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?	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