EAL

NAP: Competition (2007)

Citation:

Kirwan JP, O'Gorman DJ, Cyr-Campbell D, Campbell WW, Yarasheski KE, Evans WJ. Effects of a moderate glycemic meal on exercise duration and substrate utilization. Med Sci Sports Exerc. 2001; 33 (9): 1,517-1,523.

PubMed ID: 11528341

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 determine the effects of a breakfast cereal with a moderate glycemic index on endogenous glucose production and substrate oxidation during continuous moderate-intensity cycling exercise.

Inclusion Criteria:

Normal, healthy, active women, all taking part in recreational sports activities
Subjects were initially screened for exercise training and menstrual and smoking status
All participants had normal response to 75-gram oral glucose tolerance test.

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 consumed 75g carbohydrates in the form of rolled oats mixed with 300ml water or water alone
Meal or water was ingested 45 minutes prior to performing cycling exercise to exhaustion (60% of peak VO₂).

Statistical Analysis

Differences between dependent variables examined with one-way ANOVA or Student's T-tests
Specific mean differences were identified with Newman-Keuls post-hoc test.

Data Collection Summary:

Timing of Measurements

Muscle biopsies taken before and immediately after exercise
Heart rate measured continuously
Blood samples were drawn before the test meal, at 15, 30 and 45 minutes after the meal and at 30-minute intervals during exercise until exhaustion
Gas exchange measured during the first 30 minutes of exercise and when blood was sampled.

Dependent Variables

Blood samples drawn for glucose, glucose kinetics, FFA, glycerol, insulin, epinephrine and norepinephrine
Muscle biopsies obtained from vastus lateralis for muscle glycogen
Glucose kinetics determined using glucose tracer
Heart rate measured using radiotelemetry
Gas exchange measurements and RER determined by indirect calorimetry.

Independent Variables

75g carbohydrate in the form of rolled oats mixed with 300ml water or water alone, ingested 45 minutes prior to testing
Subjects required to reside in General Clinical Research Center for two days and three nights to control physical activity and diet before the rides.

Description of Actual Data Sample:

Initial N: Six active women
Attrition (final N): Six
Age: Mean, 24±2 years
Ethnicity: Not mentioned
Location: Pennsylvania.

Summary of Results:

Other Findings

There was a significant increase in plasma glucose and insulin after ingesting the test meal, when compared to the control trial; 45 minutes after the meal, glucose and insulin levels were still significantly higher than the control trial (P<0.05)
Compared with water-only, plasma FFA and glycerol levels were suppressed (P<0.05) for the first 120 minutes of exercise for the rolled oats trial
RER was also higher (P<0.05) during the first 120 minutes of exercise for the rolled oats trial, indicating a greater reliance on carbohydrates as an energy source
At exhaustion, glucose, insulin, FFA, glycerol, epinephrine, norepinephrine, RER and muscle glycogen were no different between trials
Glucose kinetics were greater (P<0.05) during the rolled oats trial, compared with water-only (2.36±0.22 and 1.92±0.27mg per kg per minute, respectively)
Exercise duration was 5% longer during the rolled oats trial, but the mean times were not significantly different (253.6±6 and 242.0±15 minutes, respectively)
There were no differences between trials in terms of heart rate.

Author Conclusion:

In conclusion, the results indicate that ingestion of a moderate glycemic meal containing 75g carbohydrates, 45 minutes before cycling exercise at about 60% of peak VO₂, did not alter exercise duration
Ingestion of the rolled oats meal led to an increase in circulating insulin at the beginning of exercise that was sufficient to maintain the suppression of FFA release and fat oxidation for the first two hours of exercise
Thus, there was no apparent sparing of glucose early in exercise and although glucose kinetics were higher during the latter period of exercise, it was not sufficiently increased to make a difference in terms of providing the carbohydrates necessary to sustain exercise for a longer duration. However, these data do not indicate any negative effects arising from the ingestion of a small meal with a moderate glycemic index before moderate-intensity continuous exercise, even when there is a marked insulin response to the ingested meal.

Funding Source:

Government:

NIH

Industry:

Quaker Oats Inc

Food Company:

University/Hospital:

Penn State University, Case Western Reserve University School of Medicine at MetroHealth Medical Center, Medical Center, Purdure University, University of Arkansas for Medical Sciences

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

Subjects lived at GCRC prior to testing
Authors note that 75g may not be large enough to see significant effects
No power calculations done.

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?	???
	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?	???
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?		???
	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?	N/A
	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?	???
	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