EAL

NAP: Training (2007)

Citation:

Tarnopolsky MA, Atkinson SA, Phillips SM, MacDougall JD. Carbohydrate loading and metabolism during exercise in men and women. J Appl Physiol. 1995; 78 (4): 1,360-1,368.

PubMed ID: 7615443

Study Design:

Randomized controlled trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To examine selected metabolic and performance variables in male and female endurance athletes during submaximal exercise under conditions of moderate (55%-60%) and high (75%) carbohydrate intakes.

Inclusion Criteria:

Men selected on basis of training history demonstrating at least six months of consistent endurance-type physical activity at a frequency of four times per week and VO_2peak of at least 60ml per kg per minute
Women matched in training history and VO_2peak of at least 50ml per kg per minute
Females eumenorrheic for two years before testing and tested during midfollicular phase.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Athletes volunteered for the study, selected based on training history and VO_2peak
Design: Randomized controlled trial in counter-balanced design
Blinding used: Not used; lab tests
Intervention: High-CHO or moderate-CHO diet for five days.

Statistical Analysis

Physical characteristics of subjects compared with independent T-est
Data analyzed as two-way ANOVA with gender as between factor and diet as other variable
Data expressed as absolute change from low- to high-CHO diets and expressed as 95% confidence interval
Correlations between muscle glycogen and performance times examined using simple linear regression. All other data analyzed by using between-within split-plot ANOVA with group as between-subject variable and diet and time as two within-subject variables. When a significant within-group F-ratio was obtained, the location of pairwise differences was performed with Student-Newman-Keuls post-hoc test.

Data Collection Summary:

Timing of Measurements

During each five-day experimental protocol, subjects assigned to low- or high-CHO for five days and cycled 90, 60 and 30 minutes per day at 65% VO_2peak for the first three days, rested on the fourth day and the fifth day was the exercise trial day
Blood samples taken before exercise and at 20, 40, 60 minutes of exercise, at 20 min of recovery and after a final fatigue trial
Muscle biopsies taken before and after exercise.

Dependent Variables

Urine collected on rest and exercise days for urinary urea nitrogen
Blood samples analyzed for lactate, glucose, hemtocrit, urea, glycerol, potassium, sodium and FFA
Muscle biopsies from vastus lateralis for analysis of muscle glycogen and lactate content
Gas exchange measurements
Ratings of perceived exertion.

Independent Variables

High-CHO (75% CHO) or low-CHO (55%-60% CHO)
Diets isoenergetic to habitual diets from four-day food records
Food was provided and subjects recorded all foods to maximize compliance.

Description of Actual Data Sample:

Initial N: 15 athletes; seven male, eight female
Attrition (final N): 15

Age

Men, mean: 23.3±3 years
Women, mean: 22.5±2.1 years.

Ethnicity

Not mentioned.

Anthropometrics

Men and women not significantly different in terms of age or training history
Significantly different in terms of weight, lean body mass, body fat percentage, height and VO_2peak, which are explained by gender differences (P<0.05).

Location

Canada.

Summary of Results:

	Men	Women	P-Value
Power Output; 75% Trial (W)	245±19	169±10	<0.001
Power Output; 75% Trial (W/kg LBM)	3.8±0.4	3.6±0.3	NS
Power Output; 85% Trial (W)	294±22	188±11	<0.001
Power Output; 85% Trial (W/kg LBM)	4.6±0.4	4.0±0.3	<0.05
Time to Fatigue; 85% Trial, Low-CHO (minutes)	13.0±7.6	14.0±11.3	NS
Time to Fatigue; 85% Trial, High-CHO (minutes)	18.9±8.1	14.7±14.5	NS
Change	5.9±5.8	0.7±10.1

Other Findings

Reported compliance over 95%
Glycogen concentrations decreased after one hour of exercise for both groups with no gender differences (P<0.001)
The men increased muscle glycogen concentration by 41% in response to the dietary manipulation and had a corresponding increase in performance time during an 85% VO_2peak trial (45%), whereas the women did not increase glycogen concentration (0%) or performance time (5%)
The women oxidized significantly more lipid and less carbohydrate and protein, compared with the men during exercise at 75% VO_2peak.

Author Conclusion:

This study has demonstrated that women do not increase muscle glycogen concentrations in response to an elevation in the percentage of dietary carbohydrates from 60% to 75% by a modified carbohydrate-loading regimen
The women also oxidized less carbohydrate and protein and more lipid during endurance exercise at 75% VO_2peak, compared with training-matched men
Knowledge of these gender differences is important because nutritional recommendations on the basis of data collected by using predominantly male subjects may not be valid for women. In addition, this study highlights the need to control for the potential of confounding effect of gender in any physiological study.
Given the implications of the gender differences described in this study, it is important that future studies attempt to reproduce these findings and further explore the mechanisms behind such differences.

Funding Source:

Government:

NSERC (Canada)

Industry:

Gatorade

Food Company:

Reviewer Comments:

Low CHO of 55%-60% represented habitual intake rather than low intake.

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?		Yes
	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?	N/A
	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.)	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?		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?	???
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