NAP: Recovery (2007)

Citation:

Jentjens RLPG, Van Loon LJC, Mann CH, Wagenmakers AJM, Jeukendrup AE. Addition of protein and amino acids to carbohydrates does not enhance postexercise muscle glycogen synthesis. J Appl Physiol. 2001 Aug; 91 (2): 839-846.

PubMed ID: 11457801
 
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 whether coingestion of an insulinotropic amino acid mixture and a high rate of CHO intake (1.2g per kg per hour) provided at 30-minute intervals would increase the rate of muscle glycogen resynthesis in the post-exercise recovery period, compared with a high-CHO intake only.
Inclusion Criteria:
Male cyclists that trained at least three times per week for >two hours per day and had been involved in endurance training for at least three to five years.
Exclusion Criteria:
None mentioned.
Description of Study Protocol:
  • Recruitment: Methods not described
  • Design: Randomized crossover trial
  • Blinding used: Single-blind; lab tests.

Intervention

  • Subjects completed two trials separated by one week
  • After the glycogen depleting exercise, subjects received either CHO-only (1.2g per kg per hour) or CHO + protein (1.2g per kg per hour + 0.4g protein per kg per hour) during a three-hour recovery period.

Statistical Analysis

  • Two-way (time x treatment) ANOVA for repeated measurements was used to compare differences in glycogen, insulin and glucose concentrations
  • When analyses revealed significant differences, Tukey's post-hoc test was used to locate the difference
  • Plasma glucose and insulin responses were calculated as areas under the curve
  • Statistical analysis of these data were calculated using paired Student's T-test.
Data Collection Summary:

Timing of Measurements

  • Muscle biopsies were obtained immediately, one hour and three hours after exercise
  • Blood samples collected immediately after the exercise bout and every 30 minutes thereafter
  • Subjects completed questionnaires immediately after exercise and every hour thereafter.

Dependent Variables

  • Muscle biopsies taken from vastus lateralis
  • Blood samples analyzed for glucose and insulin
  • Gastrointestinal discomfort assessed through questionnaire.

Independent Variables

  • CHO-only (1.2g per kg per hour) or CHO + protein (1.2g per kg per hour + 0.4g protein per kg per hour) during a three-hour recovery period
  • Subjects completed a diet and activity log for recording dietary patterns to be followed before both trials.
Description of Actual Data Sample:
  • Initial N: Eight male cyclists
  • Attrition (final N): Eight, muscle glycogen only obtained in seven subjects
  • Age: 27.1±2.6 years
  • Ethnicity: Not mentioned
  • Location: United Kingdom.
Summary of Results:

Variables

CHO CHO + Protein

Glycogen Content: Zero hours

106±19 176±31

Glycogen Content: One hour

141±25

211±41

Glycogen Content: Three hours

225±22

252±48

Synthesis Rate: Zero to one hour 35±34 35±31
Synthesis Rate: One to three hours 42±9 21±16
Synthesis Rate: Zero to three hours 40±10 25±16

Other Findings

  • Plasma insulin was significantly higher in the CHO + protein trial compared with the CHO trial (P<0.05)
  • No difference was found in plasma glucose or in the rate of muscle glycogen synthesis between the CHO and CHO + protein trials
  • In general, subjects reported non-severe GI symptoms.
Author Conclusion:
  • The results of the present study do suggest that a further increase in the insulin concentration by additional supplementation of protein and amino acids does not increase the rate of glycogen synthesis when CHO intake is sufficient and supplemented at regular intervals of less than 30 minutes
  • Insulin can, therefore be excluded as the limiting factor for glycogen synthesis
  • The total amount of glucose intake post-exercise seems to play a more important role when maximal rates of muscle glycogen synthesis are required
  • An intake of 1.2g per kg per hour or more seems to be required to achieve the maximal glycogen resynthesis rate.
Funding Source:
Industry:
SmithKline Beecham Consumer Healthcare (UK)
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:
  • Inclusion criteria, exclusion criteria and recruitment methods were not well-defined
  • Muscle glycogen only measured in seven subjects
  • No power calculations were done
  • Drinks were not isoenergetic.
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? ???
  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) 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? 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.) 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? ???
  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? 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? 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