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NAP: Training (2014)

Citation:

Lima-Silva AE, Pires FO, Bertuzzi R, Silva-Cavalcante MD, Oliveira RSF, Kiss MA, Bishop D. Effects of a low or high carbohydrate diet on performance, energy system contribution and metabolic responses during supramaximal exercise. Applied Physiology, Nutrition, and Metabolism, 2013; 38 (9): 928-934.

 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To examine the effects of a high or low CHO diet on time to exhaustion (TTE), aerobic and anaerobic contribution during supramaximal exercise.
Inclusion Criteria:
  • Familiar with supramaximal/high-intensity exercise
  • Non-smoking, not taking dietary supplements or medication, free from neuromuscular disorders or CV dysfunctions.
Exclusion Criteria:
NR.
Description of Study Protocol:

Recruitment

NR.

Design

Randomized crossover trial; subjects reported to lab on six occasions:

  1. Anthropometric measurements, VO2max test and lactate threshold
  2. 72 hours after Visit One: Supramax (TTE at 115% VO2max) trial (after overnight, 12-hour fast) after following their normal diet for 48 hours (control test)
  3. 72 hours after Visit Two: Muscle glycogen depletion protocol (cycle 90 minutes at fixed workload, then HIIT protocol; six one-minute bouts of 125% VO2max interspresed with one-minute rest periods), then assigned to either high- or low-CHO diet for 48 hours
  4. 48 hours after Visit Three (on diet for 48 hours): Second supramax trial, then one-week wash-out period
  5. Repeat Visit Three; assigned opposite diet for 48 hours
  6. Repeat Visit Four.

Intervention

  • Assigned to low- or high-CHO diet for 48 hours pre-supramax trial
  • Low: 25% CHO, 45% fat, 30% PRO
  • High: 70% CHO, 20% fat, 10% PRO
  • Daily energy intake estimated from 24-hour recalls; received food lists and portion sizes for each diet; asked to record all food intake for 48-hour period.

Statistical Analysis

  1. One-way ANOVA with repeated measures to assess differences among diets, TTE, aerobic and anerobic contribution for three diets (control, low- and high-CHO)
  2. Two-way ANOVA with repeated measured for plasma and blood parametersto examine time-x-condition.
Data Collection Summary:

Timing of Measurements

  • Blood samples taked before, upon subjects reaching exhaustion and during recovery (five minutes) of the supramaximal exercise testing
  • VO2 measured breath-by-breath during all testing.

Dependent Variables

  • VO2, power
  • TTE
  • Aerobic and anaerobic contribution
  • Blood and plasma metabolites and hormones (lactate, glu, insulin, K).

Independent Variables

Dietary condition: Control, low-CHO, high-CHO.

Control Variables

  • Dietary intake recorded
  • Washout period between conditions
  • Muscle glycogen depletion protocol
  • Timing of measurements.
Description of Actual Data Sample:
  • Initial N: Six males
  • Attrition (final N): Six
  • Age: 29.7±7.6 years
  • Ethnicity: NR
  • Other relevant demographics
    • Familiar with supramax/high-intensity exercise
    • VO2max: 46.7±10.9ml per kg per minute.
  • Anthropometrics
    • Height: 179.3±4.4cm
    • BM: 75.8±10.0kg
    • BF: 13.0±2.7%.
  • Location: Sao Paulo, Brazil.
Summary of Results:

Key Findings

  • The low-CHO diet reduced TTE, compared to both the control and high-CHO diet (-19% and -32%, respectively; P<0.05)
  • This reduced TTE was accompanied by a lower total aerobic energy contribution (-39%) compared wtih the high-CHO diet (P<0.05)
  • Low-CHO diet was also associated with lower blood lactate concentration, but no effect on insulin, glu, or K.
Author Conclusion:
A low-CHO diet reduces both performance (TTE) and total aerobic energy provision during supramax exercise.  
Funding Source:
Other: not reported
Reviewer Comments:
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? No
  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? N/A
  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.) 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? N/A
  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? N/A
  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.) N/A
  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? Yes
  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? N/A
  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? Yes
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? ???
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes