EAL

NAP: Training (2007)

Citation:

Carey AL, Staudacher HM, Cummings NK, Stepto NK, Nikolopoulos V, Burke LM, Hawley JA. Effects of fat adaptation and carbohydrate restoration on prolonged endurance exercise. J Appl Physiol. 2001; 91: 115-122.

PubMed ID: 11408421

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 fat adaptation on metabolism and performance during five hours of continuous exercise.

Inclusion Criteria:

Well-trained competitive male cyclists or triathletes.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not specified
Design: Randomized crossover trial
Blinding used: Not possible to completely blind subjects to treatment diets
Intervention: High-CHO or high-fat diet for six days.

Statistical Analysis

Two trials compared by using two-factor (diet and time) ANOVA with repeated measures
Separate analyses undertaken to compare data from 20-minute rides on Days One, Four and Six and data collected at different time points during the experimental ride
Newman-Keuls post-hoc tests undertaken when ANOVA revealed significant interaction
Differences in dietary intakes, estimated glycogen utilization and time trial performances compared using Student's T-tests.

Data Collection Summary:

Timing of Measurements

Standard CHO diet for one day, followed by dietary manipulations for six days
On Day Eight, subjects consumed high-CHO diet and rested and on Day Nine, subjects consumed pre-exercise meal and then cycled for four hours at 65% peak O₂ uptake, followed by a one-hour time trial
Nine-day trials separated by 18-day washout period.

Dependent Variables

Blood samples analyzed for plasma glucose, FFA, insulin, lactate and glycerol
Heart rate monitored via Polar Accurex Plus monitor
Gas exchange measurements
Athletic performance through time trial.

Independent Variables

Consumed standard CHO diet for one day (nine grams CHO per kg per day, 1.8g fat per kg per day, 2.2g protein per kg per day)
Assigned to isoenergetic high-CHO diet (11g CHO per kg per day, one gram fat per kg per day) or high-fat diet (2.6g CHO per kg per day, 4.6g fat per kg per day) for six days
All meals and snacks supplied to subjects.

Description of Actual Data Sample:

Initial N: Seven subjects, all male
Attrition (final N): Seven subjects; one did not complete high-fat diet testing
Age: Mean, 23.9±5.6 years
Ethnicity: Not mentioned

Other Relevant Demographics

Mean body mass: 74.9±4.4kg
VO_2peak: 5.06±0.26L per minute

Location

Australia.

Summary of Results:

Other Findings

Subjects consumed 19,370±415kJ of energy on the high-CHO diet (68% CHO, 16% fat, 16% protein) and 19,179±439kJ on the high-fat diet (16% CHO, 68% fat, 16% protein)
Compared with baseline, six days of high-fat diet reduced RER with cycling at 65% peak O₂ uptake (0.78±0.01 vs. 0.85±0.02, P<0.05)
RER was restored by one day of high-CHO diet, pre-exercise meal and CHO ingestion (0.88±0.01, P<0.05)
RER was higher after high-CHO than high-fat (0.85±0.01, 0.89±0.01 and 0.93±0.01 for Days Two, Eight and Nine respectively, P<0.05)
Fat oxidation during the four-hour ride was greater (171±32 vs. 119±38g, P<0.05) and CHO oxidation lower (597±41 vs. 719±46g, P<0.05) after high-fat
Power output was 11% higher during the time trial after high-fat diet than after high-CHO diet (312±15 vs. 279±20W, P=0.11), but there were no statistically significant differences in the distance covered during the one-hour cycling time trial.

Author Conclusion:

In conclusion, this is the first investigation to determine the effects of a high-fat diet and CHO restoration on metabolism and performance during ultra-endurance exercise
We found that six days of exposure to a high-fat, low-CHO diet, followed by one day of CHO restoration, increased fat oxidation during prolonged submaximal exercise, yet despite this sparing of CHO, this study failed to detect a statistically significant benefit to performance of a one-hour time trial undertaken after four hours of continuous cycling.

Funding Source:

Government:

Australian Institute of Sport

Industry:

Nestle Australia

Food Company:

Reviewer Comments:

Recruitment methods, inclusion criteria and exclusion criteria were not well-defined
Food supplied to subjects
Small sample size may have led to insignificant results; no power calculations were done
Muscle glycogen was not measured.

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