NAP: Training (2007)


Achten J, Halson SL, Moseley L, Rayson MP, Casey A, Jeukendrup AE. Higher dietary carbohydrate content during intensified running training results in better maintenance of performance and mood state. J Appl Physiol. 2004; 96: 1,331-1,340.

PubMed ID: 14660506
Study Design:
Randomized crossover trial
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Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To determine whether subjects who consume a diet containing approximately 8.5g CHO per kg per day during a period of intensified training are better able to maintain physical performance and mood state (i.e., show fewer symptoms of over-reaching) than subjects consuming a diet containing approximately 5.5g CHO per kg per day (65% vs. 41% of total energy intake, respectively).
Inclusion Criteria:
Subjects had to have run more than 50km per week for the previous two months, have at least five years of running experience and have a personal best for 10km below 40 minutes.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:
  • Recruitment: Recruitment methods not defined
  • Design: Randomized crossover trial
  • Blinding used: Not used; lab tests.


Subjects performed two 11-day trials, consuming either the high-CHO or control diet, separated by a 10-day washout period.

Statistical Analysis

  • Two-way ANOVA for repeated measures was used to identify differences between the high-CHO and control trials in variables measured over time
  • In case of significant interactions, ANOVA for repeated measures was repeated for high-CHO and control trials separately, followed by Student's T-tests with a Bonferroni correction between individual days to detect differences within each trial over time
  • Nutrient components of the two diets, global mood scores and substrates used on the last day of the two trials were compared by Student's T-test.
Data Collection Summary:

Timing of Measurements

  • Pretrial measurements followed by two 11-day dietary intervention trials
  • The last week of both trials consisted of intensified training
  • Subjects tested in the lab on Days One, Five, Eight and 11 of both trials.

Dependent Variables

  • Pre-trial graded exercise test to exhaustion
  • Body mass, height, body fat, heart rate
  • Blood samples collected and analyzed for lactate, glucose, free fatty acids, glycerol
  • Urinalysis for urinary nitrogen concentration
  • Performance was measured with one hour steady-state running at two different speeds, followed by self-paced eight-km all-out treadmill run
  • On Days Two through Four, subjects trained for one hour at an intensity eliciting 75% maximal heart rate
  • On Days Six, Seven, Nine and 10, subjects were asked to run a 16-km outdoor course as fast as possible
  • Substrate utilization was measured with indirect calorimetry and continuous glucose infusion during 30 minutes of running at 58% and 77% VO2max
  • Training diaries kept for sleeping pattern and exercise performed
  • Daily Analysis of Life Demands of Athletes questionnaire
  • Short Profile of Mood States questionnaire
  • Muscle soreness chart.

Independent Variables

  • Two 11-day trials separated by 10-day washout period
  • During each trial, subjects received either approximately 65% CHO or approximately 40% CHO diet
  • All foods provided.
Description of Actual Data Sample:
  • Initial N: 16 male endurance-trained runners recruited  
  • Attrition (final N): Seven completed both 11-day trials fully
  • Age: Mean, 28.7±2.6 years 
  • Ethnicity: Not mentioned. 

Other Relevant Demographics

Mean body fat percentage 13.2±2.3%.


United Kingdom.

Summary of Results:

Other Findings

  • No differences observed in energy intake between diet periods and subjects were weight-stable
  • High CHO trial: 65.0±0.1% CHO, 21.9±0.4% fat, 13.1±0.4% protein
  • Control: 40.6±0.1% CHO, 43.6±0.4% fat, 15.6±0.4% protein
  • Time to complete eight km was negatively affected by the intensified training
  • Time significantly increased by 61±23 and 155±38 seconds in the high-CHO and control trials, respectively
  • Running speed on Day 11 was significantly lower during the control trial, compared with the high-CHO trial (P<0.05)
  • The 16-km times were significantly increased (by 8.2±2.1%) during the control trial only
  • Muscle soreness scores were not different between trials at any time point during the two trials
  • The Daily Analysis of Life Demands of Athletes questionnaire showed significant deterioration in mood states in both trials, whereas deterioration in global mood scores, as assessed with the Profile of Mood States, was more pronounced in the control trial
  • Scores for fatigue were significantly higher in the control trial, compared with the high-CHO trial
  • CHO oxidation decreased significantly from 1.7±0.2 to 1.2±0.2g per minute over the course of the control trial, which was completely accounted for by a decrease in muscle glycogen oxidation and an increase in fat oxidation
  • During the high-CHO trial, CHO and fat oxidation rates remained stable
  • A 33% difference in muscle glycogen oxidation between high-CHO and control trials was observed during exercise, but this difference was not statistically significant (P=0.093 and P=0.053 for the 58% and 77% VO2max, respectively).
Author Conclusion:
  • In summary, the present study indicates that consuming a diet containing approximately 8.5g CHO per kg per day (approximately 65% energy), compared with approximately 5.5g CHO per kg per day (approximately 40% energy), results in better maintenance of physical performance and mood state over the course of a period of intensified training, thereby reducing the symptoms of over-reaching
  • During the control trial, subjects showed a larger decrement in running performance and their mood was altered to a greater extent, compared with the high-CHO trial
  • Muscle glycogenolysis showed a trend to be lower on the last day of the control trial, compared with the last day of the high-CHO trial
  • This decrease in muscle glycogenolysis is most likely the result of decreased pre-exercise glycogen concentration
  • It can be concluded that dietary CHO and possibly muscle glycogen content play a role in the development of over-reaching.
Funding Source:
Government: Centre for Human Sciences of the UK Ministry of Defence Scientific Research Programme
Kelloggs UK
Food Company:
In-Kind support reported by Industry: Yes
Reviewer Comments:
  • Only seven of 16 completed both trials fully; unclear whether demographic data or statistical analysis represents all subjects or only completers
  • Food provided to subjects.
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? ???
  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? ???
  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%.) ???
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? ???
  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? N/A
  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? 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)? ???
  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