EAL

NAP: Training (2014)

Citation:

Little JP, Chilibeck PD, Ciona D, Forbes S, Rees H, Vandenberg A, Zello GA. Effect of low- and high-glycemic-index meals on metabolism and performance during high-intensity, intermittent exercise. Int J Sport Nutr Exerc Metab. 2010 Dec; 20(6): 447-456.

PubMed ID: 21116017

Study Design:

Randomized Crossover Trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To investigate the effects of low-glycemic-index and high-glycemic-index (GI) meals on metabolism and performance during high-intensity, intermittent exercise.

Inclusion Criteria:

Male athletes.

Exclusion Criteria:

Not described.

Description of Study Protocol:

Design

Participants completed three 90-minute high-intensity intermittent running trials in a single-blinded random order, separated by approximately seven days, while fasted (control) and two hours after ingesting an isoenergetic low-GI (lentil) or high-GI (potato and egg white) pre-exercise meal.

Participants made five visits to the laboratory over the course of approximately six weeks. Preliminary testing included a VO₂ peak test and a familiarization session for the high-intensity intermittent running protocol. Each participant underwent three experimental trials separated by approximately seven days in a counterbalanced, randomized crossover design. A different pre-exercise meal condition was administered in each trial.

Blinding Used

Single blinded study.

Intervention

The low-GI meal provided 1.5g of available carbohydrate per kg of body mass. The high-GI meal was matched for macronutrient content with the low-GI meal.

Energy Content and Macronutrient Profile of the Test Meals

	Low GI, high protein	High GI, high protein
Energy (kJ per kg)	-38	-38
Total carbohydrate (g per kg)	1.5	1.5
Dietary fiber (g per kg)	0.36	0.06
Protein (g per kg)	0.72	0.72
Fat (g per kg)	0.03	0.03
GI	-26	-76

GI = Glycemic index.

Statistical Analysis

Repeated-sprint performance (total distance covered over five sprints) and muscle glycogen concentration were analyzed using a one-factor (meal condition) repeated measures ANOVA. Capillary blood glucose and lactate concentration, VO₂, heart rate, RPE, serum measures and expired-gas parameters were all analyzed by two-factor (Meal Condition x Time) repeated-measures ANOVAs. The significance level was set at P<0.05. Bonferroni post hoc tests were used when significance was found. All results are reported as M±SD, except on graphs, where results are presented as M±SEM for clarity.

Data Collection Summary:

Timing of Measurements

The proportion of time spent at each speed was based on time-motion analysis of professional soccer players that demonstrated that they spend approximately 7% of the game standing still, 56% of the game walking (approximately 6km per hour), 30% of the game jogging (approximately 10km per hour), 4% of the game running (approximately 17km per hour) and 3% of the game sprinting (approximately 21km to 23km per hour)
The protocol was administered in standardized 15-minute blocks, each consisting of six walking intervals, six jogging intervals, three running intervals and eight sprints
The mean time spent during each interval, including speed transitions, was 72 seconds walking, 42 seconds jogging, 17 seconds running and 13 seconds sprinting. A 95-second standing period was incorporated into the protocol at the end of each 15-minute block to allow for blood sampling during the experimental trials.
Capillary blood samples were collected at 15 minutes, 30 minutes, 60 minutes and 120 minutes after completion of the meal
VO₂, carbon dioxide output ( VCO₂), and the respiratory exchange ratio (the ratio between VCO₂ and VO₂) were collected for seven-minute periods from the third to the tenth minute of the first, third and fifth 15-minute sections (i.e., during minutes three to 10, 33 to 40 and 63 to 70)
Muscle biopsy samples were collected at the end of the fifth 15-minute block (i.e., immediately before the repeated-sprint test)
Ratings of perceived exertion (RPE) were obtained at the end of each 15-minute section (six to 20 scale)
Post-prandial digestive symptoms of hunger, fullness, nausea, bloating and abdominal cramping were assessed using a five-point symptom-rating scale (zero, no symptoms, to four, severe symptoms) at six time points (at minutes -120, -105, -60, zero 45 and 90, where -120 minutes represents when meals are consumed before the start of exercise, which is Time Zero)
Participants were asked to complete a 24-hour diet record before each experimental trial.

Dependent Variables

Capillary blood glucose
Muscle glycogen and lactate concentration
VO₂
Heart rate
RPE
Serum FFA
Catecholamines
Insulin
Expired-gas parameters
Digestive symptoms
Exercise performance.

Independent Variables

Low GI meals
High GI meals.

Control Variables

Meals
Time interaction
Physical activity.

Description of Actual Data Sample:

Initial N

A total of 16 males:

Varsity men's soccer players: Eight
Club-level soccer players: Five
Middle-distance runners with recreational soccer experience: Three.

Attrition (Final N)

A total of 13.

Age

22.8±3.2 years.

Other Relevant Demographics

Maximal oxygen uptake tV0₂peak: 55.4±4.3ml per kg^-1 per minute^-1
Peak treadmill speed IV_max

Location

Saskatoon City Hospital, Canada.

Summary of Results:

Key Findings

There was a significant effect for total sprint distance (last exercise block), insulin levels, and free fatty acids by meal condition (P<0.01, P<0.001 and P<0.001, respectively)
Total sprint distance was significantly longer in the low-GI and high-GI test compared with the control test (P=0.01 and P=0.04, respectively)
Insulin levels were higher and free fatty acids were lower in both the low-GI and high-GI tests compared with the control test
Muscle glycogen stores were higher in both the low-GI and high-GI tests compared with the control test (P<0.05 for both). There were no differences between the low-GI and high-GI test meals.
Rate of fat oxidation was lower in both the low-GI (third 15-minute block) and high-GI (second 15-minute block) tests compared with the control test (P=0.01 and P=0.005, respectively)
During exercise, mean oxygen uptake, respiratory-exchange ratio, glucose levels and lactate levels were not different between meal conditions
There was a main effect of time for respiratory-exchange ratio and lactate levels during sprints (P<0.001 for both)
Ratings of perceived exertion (RPE) during exercise were significantly lower for the low-GI meal vs. control. There were no differences, though, between low-GI and high-GI meals.

Author Conclusion:

The current study demonstrates that both low-GI and high-GI pre-exercise meals benefit prolonged, high-intensity intermittent running performance, probably by increasing muscle glycogen availability for the late stages of exercise.

Funding Source:

Government:

Natural Sciences and Engineering Research Council (NSERC) of Canada CGS-M scholarship

Industry:

Saskatchewan Pulse Growers

Commodity Group:

Reviewer Comments:

Sample size is small
Muscle biopsies collected in a very small sample
Further studies are required to explore these findings and to study the correlation of glycogen levels and exercise performance
Exclusion criteria are not available and inclusion criteria are not reported properly
This is not a representative sample
Demographic details are required
Diet history of 24-hour recall was collected but data was not correlated with any of the end markers.

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?	No
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?	N/A
	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?		No
	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?	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?	No
	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?	???
	7.7.	Were the measurements conducted consistently across groups?	???
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?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes