• Increase Font Size
  • Decrease Font Size
  • View as PDF

NAP: Training (2014)

Citation:

Brown LJS, Midgley AW, Vince RV, Madden LA. McNaughton LR. High vs. low glycemic index three-hour recovery diets following glycogen-depleting exercise has no effect on subsequent 5km cycling time trial performance. J Sci Med Sport. 2013; 16(5): 450-454.

 
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 investigate the influence of ingesting low glycemic index (LGI) and high glycemic index (HGI) recovery meals on the metabolic responses during a short-term (three-hour) recovery period from glycogen-depleting exercise and subsequent 5km cycling trial time (TT).

Inclusion Criteria:

Cyclist.

Exclusion Criteria:

Not described.

Description of Study Protocol:
Design
  • Randomized, counter-balanced crossover
  • Visit 1: Cycling test for maximal work rate 
  • Visit two and three: A glycogen-depleting exercise followed by a three-hour recovery
  • At the start of recovery, participants immediately ate either the LGI or HGI meal
  • Participants then performed a 5km cycling time trial (TT)
  • They cycled at 100W for five minutes, followed by work rate increments of 50W every 2.5 minutes. Work rate increments of 25W were used once a heart rate of 150bpm was exceeded. A cycling cadence between 75bpm and 150bpm was maintained throughout the test. The test was terminated when the subject could not maintain a cadence of at least 75 revs per minute despite verbal encouragement. 

Blinding Used

Single-blinded.

Intervention

  • High glycemic index (HGI) or low glycemic index (LGI) meal:
    • HGI meal contained 774kcal, 140g CHO, 12g fat, 31g protein, GI=72 (cornflakes and semi-skimmed milk)
    • LGI meal contained 672kcal, 140g CHO. 13g fat, 27g protein, GI=40.  (muesli and semi-skimmed milk). 
  • Each meal provided 1g per kg body mass of CHO.

Statistical Analysis

Time trial performance between the two conditions was analyzed using the non-parametric sign test for two related samples, with the 95% CI for the median differences estimated using the Hodges-Lehmann procedure. Two-way linear mixed models were used to explore the effects of the GI and time on insulin, glucose, free fatty acid (FFA), triglyceride (TG), carbohydrate (CHO) oxidation and fat oxidation responses. Tome was modeled as a continuous variable where a linear or quadratic response was evident and as a categorical variable otherwise. Paired T-tests are reported for tests of the significance of linear slopes and quadratic effects, and omnibus F-tests are reported for all other effects in the linear mixed models. The TG data were log transformed to correct right-skewed residuals. Post-hoc pairwise comparisons with Dial adjusted P values were performed as appropriate. The Sidak at the end of the 5km TT and glucose, insulin, FFA and TG concentrations immediately post-5km TT were analyzed using paired T-tests. Oxidation rates were not compared post-TT because RER values at the end of the TT were more than 1.00 and the calculation of oxidation rates was therefore not appropriate. 

Data Collection Summary:

Timing of Measurements

Pulmonary gas exchange throughout. Venous blood was taken at 30 minutes, 120 minutes and 180 minutes post-exercise, capillary blood every 30 minutes and both at termination of TT. 

Dependent Variables

  • Free fatty acids (FFA), triglycerides (TG), insulin, glucose: Blood samples
  • Respiratory exchange ratio (RER): Pulmonary gas exchange via open circuit spirometry
  • Fat and CHO oxidation: Calculated using standard equations.

Independent Variables

LGI vs. HGI meal.

Control Variables

Same diet and training schedule during the two days before visits two and three, verified by a food intake and training diary analysis. There was no strenuous exercise, caffeine and alcohol use during the 24 hours before each visit. All testing was done at the same time of day in same lab under same environmental conditions.  

Description of Actual Data Sample:
  • Initial N: Seven males
  • Attrition (final N): Seven
  • Age: 29±9 years
  • Other relevant demographics: Maximal work rate (WRmax) was 310±48W. Cycled 150±20km per week.

Anthropometrics

  • Height: 175.8±8.9cm
  • Body mass (BM): 75.2±10.2kg.

Location

United Kingdom.

 

Summary of Results:

Findings

  • No significant difference between the median (IQR) 5km TT of either diet (P=0.45)
  • Resting values of insulin, FFA and TG were not different between two trials. Serum insulin was significantly higher at 30 minutes in HGI compared to LGI during the three-hour recovery (mean difference was 15.4pmol per L; 95% CI: 2.1 to 28.7; T=2.4, P=0.025). Post-5km cycling TT serum insulin was not significantly different between conditions (mean difference was 7.8pmol per L; 95% CI: -8.0 to 23.7; T=1.2, P=0.27).
  • No significant main effects for condition was observed for blood glucose (mean difference was 0.29pmol per L; 95% CI: -2.0 to 0.78; T=1.2, P=0.24)
  • No significant main effects for condition (F=0.6, P=0.45) or time (F=1.1, P=0.35) was observed were observed for FFA during recovery. However, the condition x time interaction was significant (F=4.9, P=0.013). Mean FFA was lower in the LGI condition at 30 minutes into recovery, but not at 120 minutes and 180 minutes.  
  • There was no significant effect for TG during recovery for condition, time or condition x time
  • Post-5km cycling TT glucose, FFA and TG were not significantly different between conditions
  • A condition x time interaction was observed where the increase in CHO oxidation rate over time was greater in HGI (mean slope difference was 0.0011g per minute; 95% CI: 0.00022g to 0.0020g per minute, T=2.5, P=0.015). A similar response was observed for RER in the change over time and the relative difference between conditions. 
  • Fat oxidation demonstrated a condition x time interaction, with a greater overall decrease in HGI (mean slope difference was 0.00052g per minute-1; 95% CI: 0.00023 to 0.00080, T=3.6, P=0.001).
Author Conclusion:

Following three hours of recovery, LGI and HGI recovery meals have greater estimated fat and CHO oxidation rates, respectively, but if the subsequent exercise duration is short, the GI of the recovery diets has no influence on recovery and subsequent performance.  

Funding Source:
Other: not described
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? Yes
  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? Yes
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%.) N/A
  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.) No
  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? 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? N/A
  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? 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? ???
  10.2. Was the study free from apparent conflict of interest? ???