NAP: Training (2007)

Citation:

Pitsiladis YP, Duignan C, Maughan RJ. Effects of alterations in dietary carbohydrate intake on running performance during a 10 km treadmill time trial. Br J Sports Med. 1996; 30 (3): 226-231.

PubMed ID: 8889116
 
Study Design:
Randomized crossover trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To examine the influence of a seven-day diet manipulation on performance during a 10-km treadmill time trial in trained runners.
Inclusion Criteria:
None mentioned; experienced male runners.
Exclusion Criteria:
None mentioned.
Description of Study Protocol:
  • Recruitment: Methods not specified
  • Design: Randomized crossover trial
  • Blinding used: Not used; lab tests
  • Intervention: Low-CHO diet or high-CHO diet manipulation for seven days
  • Statistical analysis: Two-factor ANOVA for repeated measures used, followed by Student's T-test for paired data where necessary.
Data Collection Summary:

Timing of Measurements

  • Runners ran two 10-km time trials on a treadmill set at a constant 4% gradient, each after a seven-day period of dietary manipulation, separated by a two-week washout period
  • Blood samples obtained before and immediately after each run.

Dependent Variables

  • Athletic performance measured through time trials
  • Blood samples analyzed for glycerol, glucose, lactate, FFA, hemoglobin, packed cell volume
  • Expired gas collection
  • Heart rate monitored.

Independent Variables

  • Prior to trials, subjects followed normal diet and recorded all food and drink consumed for one week
  • Isoenergetic low-CHO diet (40% CHO) consumed for seven days
  • Isoenergetic high-CHO diet (55% CHO) for four days, followed by 70% CHO for three days.
Description of Actual Data Sample:
  • Initial N: Six trained runners, all male
  • Attrition (final N): Six males
  • Age: Mean, 33±11 years
  • Ethnicity: Not mentioned.

Other Relevant Demographics

  • Mean VO2max: 67±5ml per kg per minute
  • Mean weight: 71±5kg.

Location

Scotland.

Summary of Results:

  Normal Diet Low-CHO Diet High-CHO Diet
Energy Intake (MJ) 13.7±3.2 13.8±3.3 13.8±3.2

CHO percentage

52±6

40±0

55±0, 70±0

Fat percentage

31±5

44±3

25±3

Protein percentage 13±2 14±3 12±2
Alcohol percentage
4±6 2±3 2±3

Other Findings

  • Performance time following the high-CHO (48.8±2.7 minutes) and low-CHO (48.6±2.3 minutes) diets was not different (P=0.72), nor were there any differences in running speed between conditions
  • No significant differences were found between conditions in any of the metabolites measured (blood lactate, glucose, glycerol, and plasma FFA)
  • The rate of CHO oxidation was greater on the high-CHO diet, compared to the low-CHO diet (P<0.05)
  • Heart rate was not different between conditions.
Author Conclusion:
  • In summary, these results indicate that moderate changes in the composition of the diet do not affect 10-km running performance in endurance-trained subjects
  • However, the higher rate of CHO oxidation found during the high-CHO trial suggests that the increased CHO intake had increased muscle glycogen
  • Since no difference in performance was found between conditions, this higher rate of CHO oxidation on the high-CHO trial would suggest that CHO availability was not limiting running performance in this study.
Funding Source:
Industry:
Mars Incorporated
Food Company:
Reviewer Comments:
  • Muscle glycogen not measured
  • Inclusion criteria, exclusion criteria and recruitment methods were not well-defined
  • Dietary compliance not discussed.
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? No
  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) N/A
  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? ???
  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? ???
  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)? Yes
  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