EAL

NAP: Training (2007)

Citation:

Burke LM, Hawley JA, Angus DJ, Cox GR, Clark SA, Cummings NK, Desbrow B, Hargreaves M. Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability. Med Sci Sports Exerc. 2002; 34 (1): 83-91.

PubMed ID: 11782652

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 whether the enhanced rates of fat oxidation, during submaximal exercise reported after five days of a high-fat diet in the fasting condition, persist in the face of high CHO availability before and during exercise.

Inclusion Criteria:

Well-trained male cyclists and triathletes.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not described
Design: Randomized crossover trial
Blinding used: Double-blind
Intervention: Subjects assigned to high-CHO or high-fat diet for five days prior to performance testing.

Statistical Analysis

Data from two trials were compared using two-factor (diet and time) ANOVA with repeated measures
Separate analyses were undertaken to compare data from Day One, Day Six, the first 20 minutes of steady state on Day Seven and data collected at different time points during the steady state
Newman-Keuls post-hoc tests were undertaken when ANOVA revealed a significant difference or interaction between factors
Differences in time trial performances between trials were compared using Student's T-tests.

Data Collection Summary:

Timing of Measurements

Dietary intervention for five days followed by a high-CHO diet and rest on Day Six
On Day Seven, performance testing (two-hour steady state cycling at 70% VO_2peak and time trial of seven kJ per kg was undertaken after a CHO breakfast and intake of CHO during cycling
Dietary interventions were separated by a two-week washout period.

Dependent Variables

Athletic performance measured through steady state performance ride and time trial
Rating of perceived exertion
Blood samples analyzed for plasma glucose and lactate, insulin, glycerol, FFA
Respiratory gas exchange measurements.

Independent Variables

High CHO (9.3g CHO per kg, 1.1g fat per kg, approximately 70% CHO, approximately 18% fat) or isoenergetic high-fat diet (2.5g CHO per kg, 4.3g fat per kg, approximately 70% fat, approximately 18% CHO) for five days
High-CHO diet on Day Six
CHO breakfast (two grams CHO per kg) and intake of CHO during cycling (0.8g CHO per kg per hour) on Day Seven
All meals and snacks provided to subjects based on individualized meal plans
Subjects recorded all food and drink in diaries.

Description of Actual Data Sample:

Initial N: Eight well-trained subject, all male
Attrition (final N): Eight subjects
Age: Mean age 27.9±1.7 years
Ethnicity: Not mentioned.

Other Relevant Demographics

Mean weight: 73.7±2.3kg
Mean VO_2max: 68.6±1.9ml per kg per minute

Location

Australia.

Summary of Results:

Other Findings

The high fat diet reduced respiratory exchange ratio values before and during cycling at 70% VO_2peak (0.90±0.01 on Day One to 0.80±0.01 on Day Six, P<0.05)
One day of high-CHO diet increased RER values to Day One values (0.90±0.01, 0.80±0.01, 0.91±0.01, for Days One, Six and Seven, respectively)
RER values were higher with high-CHO than high-fat diets
On Day Seven, fat oxidation remained elevated (73±4g vs. 45±3g, P<0.05), whereas CHO oxidation was reduced (354±11g vs. 419±13g, P<0.05) throughout steady state cycling in the high-fat vs. the high-CHO diet
Time trial performance was similar for both trials (25.53±0.67 minutes for high-fat vs. 25.45±0.96 minutes for high-CHO, NS)
Fasting plasma and glucose concentrations did not differ between trials or as a result of the dietary treatments.

Author Conclusion:

In conclusion, five days of a high-fat diet caused marked changes in substrate utilization during submaximal exercise
At least some of these changes were independent of CHO availability, since the enhanced capacity for fat oxidation persisted despite the restoration of muscle glycogen before and provision of exogenous CHO during exercise
Such strategies are typical of those recommended by sports nutritionists to competitive athletes
Despite promoting CHO-sparing during exercise, fat adaptation provided no benefit to the subsequent performance of a time trial lasting roughly 30 minutes
Accordingly, the results of this study do not support the practice of fat-adaptation strategies by endurance athletes competing in events of two to three hours' duration
Whether such strategies would be of benefit to ultra-endurance events lasting over four hours, where fat oxidation has the potential to meet most of the fuel requirements of work, remains to be determined.

Funding Source:

Government:

National Health and Medical Research Council (Australia), Fisheries Research and Development Corporation, Healthway

Industry:

Western Australian Fishing Industry Council

Commodity Group:

In-Kind support reported by Industry:

Yes

Reviewer Comments:

Recruitment methods, inclusion criteria and exclusion criteria were not described
Food provided to subjects
Lack of statistically significant differences may be due to small sample size.

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)	Yes
	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.)	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?	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?		???
	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