EAL

NAP: Training (2014)

Citation:

Hulton AT, Gregson W, Maclaren D, and Doran DA. (2012). Effects of GI meals on intermittent exercise. Int J Sports Med. 33:756-62.

PubMed ID: 22706944

Study Design:

Randomized Crossover Trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

The purpose of this study is to investigate the impact of high glycemic index (GI) and low GI pre-exercise meals on intermittent high intensity exercise.

Inclusion Criteria:

Male recreational football (soccer) players who train twice and week and play a weekly competitive match

Exclusion Criteria:

None mentioned

Description of Study Protocol:

Recruitment

not described.

Design

Randomized crossover trial

Blinding used (if applicable)

Not mentioned

Intervention (if applicable)

High glycemic index (GI) or low GI meal matched for macronutrient content and fluid, representing ~2g/kg body mass for a 70g participant.

Statistical Analysis

ANOVA for repeated measures on 2 factors (experimental condition and time) was used to analyze differences in the physiologic and metabolic responses in both trials. Least significant difference post-hoc tests applied as needed. A paired t-test was used to analyze time trial performance times. Differences were significant at P<.05.

Data Collection Summary:

Timing of Measurements

A venous blood sample was drawn and then 20 minutes later the participant consumed the test meal. Blood glucose samples were taken pre-meal, and at 5, 30, and 60 min post meal. About 3.5 hours after the meal, the exercise started. Blood was drawn after 10, 20, and 30 minutes and at halftime and post-exercise. Expired gas was collected during a range of exercise intensities, after the 10 min mark and ending with a low intensity bout. Perceived exertion was recorded every 5 minutes during exercise. Hunger and gut fullness ratings were recorded every 15 minutes. Heart rate was continually measured and averaged over 5 minutes.

Dependent Variables

Performance: 1 km time trial (seconds)
Blood glucose: fingerstick (pre-exercise and during exercise)
Serum insulin: venuous blood draw
Fatty acid (FA), glycerol, beta-hydroxybutyrate: venous blood draw
Lactic acid: venous blood draw
Carbohydrate and fat oxidation: expired gas
Heart rate: monitor
Perceived exertion: subjective rating from participant
Hunger/gut fullness: subjective rating from participant

Independent Variables

High glycemic index meal (138.8 g CHO, 35.7 g PRO, 23 g fat, 870 kcal, 80 GI) or low glycemic index meal (133.7 g CHO, 37.9 g PRO, 23.7 g fat, 866.3 kcal, 44 GI)

Control Variables

Two intermittent treadmill protocol trials for each participant to familiarize with the performance test

Test meal matched for macronutrient content and fluid

Size of test meal was 2g/kg body mass for a 70kg participant

Standardized breakfast on the day of the experimental tests

Abstention from alcohol and any physical exercise for 48 hours prior to each test

Description of Actual Data Sample:

Initial N: 9 males

Attrition (final N): 8 males (one had a musculoskeletal injury and could not complete the time trial)

Age: 21±3 years

Ethnicity: not mentioned

Other relevant demographics: not mentioned

Anthropometrics: 74.4 ± 4.4 kg body mass; body height 180 ± 8 cm

Location: Liverpool, United Kingdom

Summary of Results:

Key Findings

There were no significant differences between conditions for the 1km time trial (210.2 ± 19.1 s for low GI and 215.8 ± 22.6 s for the high GI). Five out of 8 participants were faster after low GI and two were faster following high GI; one produced identical results.

Other Findings

There were no significant differences in Blood Glucose were observed between conditions, but significant differences were seen for time (P=.0008) and for an interaction (P=.05). For both conditions the blood glucose concentration increased following consumption of the test meal with high GI producing a greater increase (4.6 mmol/L to 7.2 mmol/L for high GI compared to 4.9 mmol/L to 5.7 mmol/L for low GI). Blood glucose response for low GI remained more constant (mean value 4.8 mmol/L following the initial increase compared to high GI (mean value 4.0 mmol/L) prior to the start of exercise.

There were no significant differences between conditions, time, or an interaction during exercise. Blood glucose remained similar throughout exercise for both conditions.

Serum insulin concentration increased for both conditions following the test meals, with no significant differences evident between conditions, time, and interactions.

There was no significant difference between conditions or interactions for glycerol, but a significant effect of time was observed (P=.001) as glycerol concentrations increased throughout exercise.

Significant differences were observed between conditions for fatty acids (P=.022) along with a significant time effect (P=.001) but no interaction effect was noted. Fatty acid concentrations remained similar following consumption of the test meals, but low GI results in a greater increase in fatty acids rising from 0.10mmol/L at the onset of exercise to 1.70mmol/L post exercise compared to 0.07 to 1.33mmol/L for high GI.

Significant time (P=.001) and interaction (P=.001) effects were observed for beta-hydroxybutyrate with a post exercise result of 0.106mmol/L for low GI compared to 0.058mmol/L for the high GI.

Lactate concentrations increased from rest throughout exercise, with a slight decrease from half time to post exercise in high GI. No significant differences were found between conditions, but a significant difference over time was observed (P<.002) as well as significant interaction (P=.02).

Rates of carbohydrate and fat oxidation were similar thoughout both conditions. No significant condition or interaction effects were observed, but a time effect was seen for both carbohydrate (P=.012) and fat (P=.013).

Heart rate and perceived exertion increased significantly over time (P=.001), but no significant difference between conditions. Ratings of fullness and hunger showed no significant difference between conditions, over time, or an interaction.

Author Conclusion:

The type of carbohydrate ingested in a pre-match meal has no significant impact on performance or metabolic responses during 90 minutes of intermittent high intensity exercise.

Funding Source:

University/Hospital:

Liverpool John Moores University, Research Institute for Sport & Exercise Sciences (RISES)

Reviewer Comments:

The meal was more than a single food and was meant to simulate general practice in most sports.

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?	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.)	N/A
	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?		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.)	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?	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?		No
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	No
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