EAL

NAP: Recovery (2007)

Citation:

Burke LM, Collier GR, Davis PG, Fricker PA, Sanigorski AJ, Hargreaves M. Muscle glycogen storage after prolonged exercise: effect of the frequency of carbohydrate feedings. Am J Clin Nutr. 1996; 64: 115-119.

PubMed ID: 8669406

Study Design:

Randomized controlled trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To examine the importance of the greater incremental glucose and insulin concentrations on glycogen repletion, by comparing intake of large carbohydrate meals (gorging) with a pattern of frequent small carbohydrate snacks (nibbling), which simulates the flattened glucose and insulin responses after low-GI carbohydrate meals.

Inclusion Criteria:

Well-trained triathletes.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Recruited from a local pool of elite and subelite athletes
Design: Randomized controlled crossover trial
Blinding used: Not used.
Intervention: Subjects assigned to gorging and nibbling in random order.

Statistical Analysis

Data from two trials were compared with ANOVA for repeated measures
Specific differences between means were located using the Newman-Keuls post-hoc test
24-hour glycogen storage was compared between trials using paired T-tests.

Data Collection Summary:

Timing of Measurements

Subjects undertook an exercise trial (two hours at 75% VO_2max, followed by four 30-second sprints) to deplete muscle glycogen, on two occasions one week apart
For 24 hours after each trial, subjects rested and consumed the same diet, composed exclusively of high-glycemic index carbohydrate foods, providing 10g CHO per kg body mass
Venous blood samples were taken before and 30 and 60 minutes after each meal, 60 minutes after each snack
Muscle biopsies were taken at zero and 24 hours.

Dependent Variables

Muscle biopsies were taken from vastus lateralis at the beginning and 24 hours after recovery and analyzed for glycogen content using an enzymatic, fluorometric technique
Plasma glucose was measured with an automatic analyzer
Plasma insulin was measured with double-antibody radioimmunoassay kit
Plasma triacylglycerol concentrations were measured by enzymatic hydrolysis technique.

Independent Variables

Gorging trial: Provided food as four large meals of equal CHO content (10g CHO per kg body mass, composed almost entirely of high-CHO foods with high GI) eaten at zero, four, eight and 20 hours of recovery
Nibbling trial: Each meal was divided into four snacks and fed at hourly intervals (zero to 11 hours, 20 to 23 hours, nine-hour break for sleeping)
Subjects were required to stay overnight during the recovery period so that diet and exercise could be fully controlled
Standardized diet and exercise protocol to be followed for 48 hours prior to each trial: 300-400g CHO per 24 hours was provided and no training or strenuous exercise allowed for more than 36 hours prior to the trial, compliance checked with food and activity records.

Description of Actual Data Sample:

Initial N: Eight athletes, gender not mentioned
Attrition (final N): Eight
Age: Mean, 25.6±1.5 years
Ethnicity: Not mentioned
Other relevant demographics: Mean weight, 70.2±1.9kg
Location: Australia.

Summary of Results:

	Zero Hours	24 Hours	Change
Gorging	55.8±9.0	129.9±10.2	74.1±8.0
Nibbling	50.1±9.6	144.5±12.2	94.5±14.6

Other Findings

Gorging diet produced large increases in plasma glucose and insulin after each meal, which returned to baseline values within 60 to 90 minutes
Nibbling diet produced lower plasma glucose and insulin profiles over the day
Plasma triacylglycerol profile over the 24 hours was also lower during nibbling trial
Despite differences in glucose and insulin profiles, there was no significant difference in muscle glycogen storage between the two groups over the 24 hours (gorging, 74.1±8.0mmol per kg wet weight; nibbling, 94.5±14.6mmol per kg wet weight).

Author Conclusion:

In summary, the results of this study suggest that large meals were as effective as small snacks in achieving glycogen storage during 24 hours of recovery from prolonged exercise, when total carbohydrate intake was controlled and adequate
From a practical viewpoint, athletes are advised to plan a high-carbohydrate menu for post-exercise recovery and to plan the frequency of meals and snacks to suit considerations such as appetite and availability of food
In addition, the study suggests that delayed absorption, causing acute alterations to glucose, insulin and blood fat profiles, does not adequately explain the reduced rate of glycogen storage seen with low-GI carbohydrate foods and that an alternative mechanism needs to be investigated.

Funding Source:

Government:

Australian Sports Commission

Industry:

Mars Australia

Food Company:

University/Hospital:

Australian Institute of Sport, Deakin University, University of Melbourne

Reviewer Comments:

Inclusion criteria and exclusion criteria and subjects were not well-defined
Well-controlled environment.

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?	No
	2.4.	Were the subjects/patients a representative sample of the relevant population?	???
3.	Were study groups comparable?		???
	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?	???
	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?		No
	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.)	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?	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?		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)?	Yes
	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