NAP: Competition (2007)

Citation:

Whitley HA, Humphreys SM, Campbell IT, Keegan MA, Jayanetti TD, Sperry DA, MacLaren DP, Reilly T, Frayn KN. Metabolic and performance responses during endurance exercise after high-fat and high-carbohydrate meals. J Appl Physiol. 1998; 85 (2): 418-424.

PubMed ID: 9688714
 
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 investigate the metabolic and performance-related responses during endurance exercise after isoenergetic high-fat and high-carbohydrate preexercise meals and to compare these with a control situation with no pre-exercise meal.
Inclusion Criteria:
  • Endurance-trained cyclists
  • All were competing regularly in both regional and national championship events.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:
  • Recruitment: Methods not described
  • Design: Randomized crossover trial
  • Blinding used: Not used; lab tests.

Intervention

  • Subjects were studied on three occasions after an overnight fast
  • They were given isoenergetic meals containing high-fat (80g fat, 50g CHO, 14g protein per 70kg body mass) or high-CHO meal (three g rams fat, 215g CHO, 26g protein per 70kg body mass)
  • On the third occasion subjects were studied after an overnight fast
  • Four hours after consumption of the meal, subjects started exercise for 90 minutes at 70% of their maximal oxygen uptake, followed by a 10-km time trial
  • Subjects were studied one day per week for one month.

Statistical Analysis

  • Changes in metabolic and hormonal responses to meals with time during the 90-minute exercise period were assessed with ANOVA for repeated measures, as were differences in substrate oxidation and energy expenditure between dietary conditions
  • To summarize data not shown graphically and to obtain post-hoc comparisons between dietary conditions, responses were assessed as total areas under the curve over the 90-minute exercise period
  • AUCs were analyzed using repeated-measures ANOVA
  • For statistically significant values, post-hoc analysis was performed by using Tukey's honestly significant differences test.
Data Collection Summary:

Timing of Measurements

Blood samples, gas exchange measurements, heart rate and RPE obtained at rest and at 15, 30, and 60 minutes during the ride, at ride completion and in final minutes of 10-km time trial.

Dependent Variables

  • Gas exchange measured through indirect calorimetry
  • Blood samples analyzed for glucose, glycerol, lactate, 3-hydroxybutyrate, insulin, growth hormone, cortisol, epinephrine and norepinephrine, total and HDL cholesterol
  • Heart rate
  • RPE.

Independent Variables

  • Subjects fasted or were given isoenergetic meals (4,000kJ) containing high-fat (80g fat, 50g CHO, 14g protein per 70kg body mass) or high-CHO meal (three grams fat, 215g CHO, 26g protein per 70kg body mass) four hours before exercise
  • Subjects asked to keep food and activity diaries to record exercise, resting the day before each trial.
Description of Actual Data Sample:
  • Initial N: Eight males
  • Attrition (final N): Eight
  • Age: Mean, 21 years
  • Ethnicity: Not mentioned
  • Location: United Kingdom.
Summary of Results:

 

Condition Time to Completion, Seconds Mean Power, W

No meal

874±48 279±31

High-fat meal

854±37

290±29

High-CHO meal

878±44

276±33

Other Findings

  • The high-CHO meal, compared with the high-fat meal resulted in significant decreases in blood glucose, plasma non-esterified fatty acids, plasma glycerol, plasma chylomicron-triacylglycerol and plasma 3-hydroxybutyrate concentrations during exercise
  • This was accompanied by an increase in plasma insulin (P<0.01 vs. no meal), plasma epinephrine and plasma growth hormone concentrations (each P<0.05 vs. either of the other conditions) during exercise
  • No significant differences in heart rate or RPE were observed among the three trials
  • Despite the differences in substrate and hormone concentrations in plasma, substrate oxidation during the 90-minute exercise period was similar in the three trials and there were no differences in performance on the time trial. 
Author Conclusion:
  • In summary, the present study demonstrates that feeding isoenergetic meals containing different proportions of carbohydrate and fat can markedly affect the contributions of carbohydrate and fat to energy expenditure at rest, as long as four hours after the meals
  • However, the pattern of substrate oxidation during exercise is very resistant to alteration despite variations in substrate availability in plasma. 
Funding Source:
Industry:
Mars Incorporated
Food Company:
Reviewer Comments:
Inclusion criteria, exclusion criteria and recruitment methods were not well-described.
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? No
  2.2. Were criteria applied equally to all study groups? ???
  2.3. Were health, demographics, and other characteristics of subjects described? No
  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) 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%.) 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? 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? 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? 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? N/A
  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