EAL

NAP: Training (2007)

Citation:

Reznik Dolins K, Boozer CN, Stoler F, Bartels M, DeMeersman R, Contento I. Effect of variable carbohydrate intake on exercise performance in female endurance cyclists. Int J Sport Nutr Exerc Metab. 2003; 13 (4): 422-435.

PubMed ID: 14967867

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 effect of various levels of carbohydrate intake on endurance exercise performance.

Inclusion Criteria:

Eumenorrheic women who habitually cycled at least 100 miles per week
Aged 20 to 45 years.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Subjects recruited through cycling club websites and word of mouth
Design: Randomized crossover trial
Blinding used: Double-blind.
Intervention: Subjects randomly assigned to eucaloric diet providing eight, five or three grams CHO per kg body weight for six days.

Statistical Analysis

Differences in time to exhaustion across diets were examined with a singly-repeated-measures ANOVA
Doubly-repeated ANOVA were used to test differences in RPE, RER and HR across the three diets and across time during each trial
Repeated-measures one-way MANOVA was used to evaluate possible correlation between muscle mass and effect of diet on time to exhaustion
Data was incomplete for three subjects.

Data Collection Summary:

Timing of Measurements

Subjects cycled at least 100 miles while adhering to the diet for six days
Exercise trial was performed on the seventh day, consisting of a 60-minute cycle at 70% VO_2max, followed by an increase in intensity to 90% until that intensity could no longer be maintained
Three-week washout period between trials.

Dependent Variables

Time to exhaustion
Variations in heart rate measured by electrocardiograph
Respiratory exchange ratio measured by gas exchange measurements
Rating of perceived exertion determined every 15 minutes.

Independent Variables

Three-day baseline food record collected to determine preferences and RMR obtained using indirect calorimetry to estimate caloric requirements; diets were eucaloric
Carbohydrates were calculated to provide eight, five or three grams CHO per kg body weight
Menus provided with foods and portions to be consumed daily.

Control Variables

Body composition using DEXA.

Description of Actual Data Sample:

Initial N: 11 women
Attrition (final N): 11 women completed; due to incomplete data, analysis based on eight subjects
Age: Mean 32.45±6.38 years
Ethnicity: Not mentioned
Other relevant demographics: VO_2max of 60.1±5.1ml per kg
Location: New York City, NY.

Summary of Results:

Other Findings

RMR was 1,414±215kcal, total EE was 2,473±295kcal
Subjects consumed 92% of kcal prescribed. Most were unable to consume adequate CHO on the eight-gram CHO per kg per day diet. Compliance data were not available for all eight subjects; incomplete data was handed in by some subjects.
There was no diet effect on the correlation between kg of muscle and time to exhaustion
Results indicated no difference in mean time to exhaustion, heart rate or ratings of perceived exertion
Respiratory exchange ratio increased over time elapsed (F=40.4, P<0.001) and across diets (F=6.1, P=0.015).

Author Conclusion:

The main finding of this study was that there were no performance differences in female cyclists who completed a trial to exhaustion after one week on a diet supplying eight grams CHO per kg body weight vs. five grams CHO per kg body weight
There were also no significant changes in performance after one week on a diet supplying three grams CHO per kg body weight.

Funding Source:

University/Hospital:

Teachers College

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

Dietary compliance may have resulted in lack of differences between groups
Analysis based on only eight of 11 women, due to incomplete data
Authors note that the study occurred over a span of time during which training patterns varied.

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?	Yes
	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?		N/A
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	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?		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?	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?	???
	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?	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