EAL

NAP: Training (2007)

Citation:

Tarnopolsky MA, Zawada C, Richmond LB, Carter S, Shearer J, Graham T, Phillips SM. Gender differences in carbohydrate loading are related to energy intake. J Appl Physiol. 2001; 91: 225-230. PubMed ID: 11408434

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 examine whether the provision of extra energy, in conjunction with additional absolute carbohydrate, would allow women to increase muscle glycogen concentration by a similar amount, compared with men, in response to a modified dietary carbohydrate-loading protocol
Secondary objectives were to determine whether hexokinase activity or differences in the proportion of pro- and macroglycogen could explain the previously described gender differences in dietary carbohydrate-loading.

Inclusion Criteria:

Endurance-trained athletes, with a training history of consistent participation in endurance-type physical activity for at least one year (minimum five days per week and 45 minutes per session) and peak oxygen consumption of 55ml per kg per minute for men, 45ml per kg per minute for women.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Subjects volunteered for the study
Design: Randomized crossover trial
Blinding used: Double-blind
Intervention: Subjects randomly allocated to three diets for a five-day period.

Statistical Analysis

Independent T-test used to compare physical characteristics of subjects
Glycogen, diet analysis and hexokinase activity analyzed by two-way ANOVA
One-way ANOVA also used to analyze glycogen data
Newman-Keuls post-hoc test used to locate pairwise differences
Correlations between hexokinase activity and glycogen concentration were performed by using Pearson product-moment correlation analysis.

Data Collection Summary:

Timing of Measurements

Subjects consumed 3 diets for 5 days, with physical activity on days 1-3. Day 4 was a rest day. Muscle biopsies taken on Day 5.

Dependent Variables

Total, pro- and macroglycogen and hexokinase activity analyzed through muscle biopsy
Total body fat and FFM determined by DEXA.

Independent Variables

Allocated to three diets: Habitual, High-Carbohydrate (75%) and High-Energy (increased by 34%), for four days
Subjects completed baseline diet records for three weekdays and one weekend day and received instructions about dietary recording and measuring
Trial diets packaged and provided to subjects, with uneaten food returned and daily consumption recorded.

Description of Actual Data Sample:

Initial N: 13 subjects; six men, seven women
Attrition (final N): 12; six men, six women; dropout not described
Mean age: Men, 22.8±4.7 years; women, 21.7±3.7 years
Ethnicity: Not mentioned
Other relevant demographics: Women tested during midfollicular phase of menstrual cycle
Anthropometrics: Men and women did not differ significantly in terms of age and peak oxygen uptake, but did differ in terms of weight, height, FFM and body fat.
Location: Canada.

Summary of Results:

	Energy (kcal per day)	Protein Percentage	Fat Percentage	CHO Percentage	CHO (g per kg per day)
Habitual; Men	3,039±954	15±3	28±6	58±5	6.1±0.3
Habitual; Women	2,000±487	14±2	26±5	59±3	5.1±0.3
High-CHO; Men	3,042±973	10±1	15±1	75±1	7.9±0.5
High-CHO; Women	1,993±512	10±1	15±2	75±1	6.4±0.6
High-Energy; Men	4,038±1,206	11±1	14±1	75±1	10.5±0.4
High-Energy; Women	2,711±691	10±1	15±2	75±2	8.8±0.5

Other Findings

Dietary compliance was above 96%
Total glycogen concentration was higher for men on the High-Carbohydrate (660.2±120.1 vs. 537.2±78.6) and High-Energy (741.1±187.7 vs. 537.2±78.6) trials, compared with Habitual Diet (P<0.05), whereas women only increased on the High-Energy (737.7±198.1 vs. 629.1±231.1) diet, compared with Habitual (P<0.05)
There were no gender differences in the proportion of pro- and macroglycogen or hexokinase activity.

Author Conclusion:

Overall, these findings provide support for the hypothesis that the previously reported gender difference in carbohydrate loading was due to gender differences in absolute and relative carbohydrate intakes. Therefore it is unlikely that gender differences in either enzymatic capacity or glucose transport could explain the earlier observations.
Future studies should test the potential performance benefits from the dietary carbohydrate and energy manipulation proposed in this paper.

Funding Source:

Reviewer Comments:

Recruitment methods, inclusion criteria and exclusion criteria were not well-described
Unclear number of subjects (12 or 13)
Although muscle glycogen was measured, no performance data provided.

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?		???
	4.1.	Were follow-up methods described and the same for all groups?	No
	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%.)	No
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	No
	4.4.	Were reasons for withdrawals similar across groups?	???
	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?		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)?	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