EAL

NAP: Training (2007)

Citation:

Roltsch MH, Flohr JA, Brevard PB. The effect of diet manipulations on aerobic performance. Int J Sport Nutr Exerc Metab. 2002; 12 (4): 480-489.

PubMed ID: 12500991

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 examine the metabolic consequences of variations in dietary fat and carbohydrate contents that are within a range that can be reasonably expected to be consumed by endurance athletes on substrate utilization during 40 minutes of steady state exercise at 75% VO_2max.

Inclusion Criteria:

Male endurance runners required to have a VO_2max above 50ml per kg per minute on a progressive treadmill test and a minimum training regimen of three days a week for 30 minutes for the past three months.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Subjects volunteered as participants
Design: Randomized crossover trial
Intervention: Normal diet and three eucaloric experimental diets consumed for seven days prior to testing.

Statistical Analysis

Exercise data were analyzed using a mixed-model repeated-measures factorial ANOVA
The best-fitting variance-covariance structure based on the Bayesian Information Criterion was selected
The degrees of freedom method used was Kenward-Roger
For all analyses, the residuals for the dependent variable met the assumptions of variance homogeneity and normality for the ANOVA.

Data Collection Summary:

Timing of Measurements

Substrate utilization recorded at steady state (73±1.4% of VO_2max) while running on a treadmill for 40 minutes after consumption of an experimental diet for seven days
No washout periods between diets.

Dependent Variables

Substrate utilization, respiratory exchange ratio and oxygen consumption measured using metabolic cart
Heart rate recorded using heart rate monitor
Rating of perceived exertion
Fasting blood samples analyzed for lactate and glucose levels.

Independent Variables

Normal diet (3,403kcal, 16% protein, 59% CHO, 22% fat, 3% alcohol)
Fat supplemented diet (3,800kcal, 14% protein, 53% CHO, 33% fat)
High-carbohydrate diet (3,800kcal, 13% protein, 72% CHO, 15% fat)
Adjusted normal diet (3,800kcal, 16% protein, 61% CHO, 23% fat)
Subjects were given diets containing foods and amounts to consume
Subjects completed three-day food records and Seven-Day Physical Activity Recall Questionnaires.

Description of Actual Data Sample:

Initial N: Six males
Attrition (final N): Six
Age: Mean, 29.8±11 years
Ethnicity: Not mentioned.

Other Relevant Demographics

Mean weight: 72.3±10kg
Mean VO_2max: 66±10ml per kg per minute.

Location

Virginia.

Summary of Results:

	Kcal per Day	Protein Percentage	CHO Percentage	Fat Percentage	Alcohol Percentage
Normal	3,403±782	16±1.8	59±9.7	22±9.7	3±2.4
Adjusted Normal	3,800±690	16±1.6	61±8.0	23±7.9	0
High CHO	3,800±690	13±1.4	72±5.1	15±4.8	0
Fat Supplemented	3,800±690	14±1.7	53±3.7	33±3.0	0

Other Findings

The normal diet was found to be approximately 400kcal deficient
Body weight did not change during the trial periods
There were no significant differences in respiratory exchange ratio between any of the dietary manipulations
No significant differences were observed for lactate, VO₂ or heart rate during submaximal testing on the different diets.

Author Conclusion:

The results of this study indicated that for this group of male runners, the diets tested did not significantly affect substrate utilization during steady-state treadmill running
Therefore, for endurance athletes seeking to enhance their performance in a race in which their intensity is going to be greater than 73% of their VO_2max, it would be advantageous for them to consume a diet high in carbohydrates for peak performance, as previous research has indicated.

Funding Source:

Industry:

Gatorade

Food Company:

Reviewer Comments:

No washout periods between diets
Power analysis not done; small sample size
Dietary planning did not result in interventions that were eucaloric, compared to the normal diet
Muscle glycogen 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?	Yes
	2.2.	Were criteria applied equally to all study groups?	Yes
	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?		N/A
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	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?		???
	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?	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?		???
	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