EAL

NAP: Training (2007)

Citation:

Rowlands DS, Hopkins WG. Effects of high-fat and high-carbohydrate diets on metabolism and performance in cycling. Metabolism, 2002; 51 (6): 678-690.

PubMed ID: 12037719

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 compare the effects on cycling metabolism and performance of a two-week high-fat diet pre-exercise meal condition, with and without carbohydrate-loading, against a high-carbohydrate diet pre-exercise meal condition as the control.

Inclusion Criteria:

Nationally competitive male cyclists and triathletes who had trained in their sport for 7±4 years.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Not specified
Design: Randomized crossover trial
Blinding used: Not possible. To reduce bias, subjects were not informed of their performance until study completion.

Intervention

Subjects were randomized to two-week adaptation to each of three diets:

14-day high-carbohydrate
14-day high-fat
11.5-day high-fat diet, followed by 2.5-day carbohydrate-loading.

Statistical Analysis

The effects of the diets were estimated using repeated-measures analysis
Most variables were analyzed after log transformation to reduce or eliminate effects of non-uniformity of error
The trends in power output during the 100-km time trial were compared using within-subject modeling
Polynomial expressions containing linear and quadratic components were fitted to blood lactate concentration
Percentage dietary fat and peak fat oxidation rate were included as covariates in separate repeated-measures analyses with the treatment effect.

Data Collection Summary:

Timing of Measurements

Each subject performed metabolic and performance tests before and after each of the two-week dietary treatment conditions

There were two exercise procedures in each two-week treatment block: A short incremental test on Day 11 to measure peak power and VO_2max; the five-hour testing procedure on Day 14 to measure effects of the diets on metabolism and performance.

Dependent Variables

Exercise test lasted approximately five hours and comprised a 15-minute short-endurance trial, an incremental test to measure the peak fat-oxidation rate and a 100-km trial
Expiured respiratory gas collected for determination of oxygen consumption and carbon dioxide production
Blood samples analyzed for lactate, insulin, glucagon, glucose, urea, free fatty acid and glycerol concentrations
Urine samples collected for analysis of renal urea clearance.

Independent Variables

Two-week adaptation to each of three diets

14-day high-carbohydrate (70% CHO, 15% fat and 15% protein)
14-day high-fat (70% fat, 15% protein, 15% CHO)
11.5-day high-fat diet followed by 2.5-day carbohydrate-loading.

To assist with adherence, subjects were provided with food composition tables, measuring containers and menus. Appropriate food items were purchased for the subjects and regular contact between investigators and subjects encouraged compliance, which was also monitored through four-day diet diaries.
Conditions included a pre-exercise meal of the same composition as the preceding diet 80 or 90 minutes before exercise
Each condition preceded by two-week standardizing normal diet (50% CHO, 35% fat, 15% protein)
Sports bars and a 5% carbohydrate solution were ingested during the tests.

Description of Actual Data Sample:

Initial N: Seven male cyclists

Attrition (final N): Seven cyclists

Age: 27±5 years

Ethnicity: Not mentioned

Other relevant demographics: Body fat, 8±3%

Location: New Zealand.

Summary of Results:

	CHO	Fat	Fat CHO
15-minute test; distance (km)	11.0±0.5	11.0±0.4	11.0±0.5
15-minute test; treatment effect (percentage)	-0.9±2.0	1.8±2.0	0.5±2.1
15-minute test; power (W)	305±40	310±30	308±38
15-minute test;treatment effect (percentage)	-2.1±4.3	-5.0±4.1	-0.7±4.3
100-km trial; time (minutes)	156±12	156±13	155±9
100-km trial; treatment effect (percentage)	1.6±4.1	-2.5±4.3	-1.8±3.7
100-km trial; power (W)	217±44	212±40	223±27
100-km trial; treatment effect (percentage)	-4.5±9.0	6.3±12.9	3.4±10.8

Other Findings

Percentage macronutrient composition was similar to that of prescribed: High-carbohydrate (14%±2% protein, 70%±9% CHO, 16%±5% fat); high-fat (20%±3% protein, 15%±4% CHO, 66%±10% fat); high-fat CHO-load (20%±3% protein, 15%±3% CHO and 65%±9% fat for high-fat days, 13%±4% protein, 63%±22% CHO and 24%±10% fat during CHO-load)
The diets had no statistically significant effect on 15-minute performance, although the high-fat condition tended to reduce distance covered by -2.4% (95% confidence interval: -5.4% to +0.6%, P=0.11) relative to the fat with carbo-loading condition
In the 100-km time trial, the high-fat and the fat with carbohydrate-loading conditions attenuated the decline in power output observed in the high-carbohydrate condition (P=0.03 to 0.07), although the corresponding improvement in performance time of 3% to 4% (-2% to 10%) was not statistically significant (P=0.16 to 0.22)
Power output during the final five km of the time trial in the fat with carbo-loading condition was 1.3-fold (1.0 to 1.6, P=0.04) greater than in the high-carbohydrate condition
Overall, for every 10% of energy increase in dietary fat, 100-km mean power increased by 2% (-0.0% to 4%, P=0.06)
Relative to the high-carbohydrate condition, the high-fat conditions resulted in the following metabolic changes consistent with greater lipolysis and fuel availability: Lower plasma insulin concentration before exercise (P<0.0001) and during exercise a 10% to 20% higher plasma-glucose concentration (P<0.01); higher plasma glycerol (P<0.05) and a 2.5-fold to 2.9-fold increase in the peak fat oxidation rate (P<0.0001).

Author Conclusion:

The two-week high-fat diet conditions increased fat availability and substantially enhanced the peak fat-oxidation rate during exercise
Despite these effects on metabolism, the main ultra-endurance performance outcomes were not statistically significant. Nevertheless, there was evidence for a substantial enhancement of ultra-endurance cycling performance in the high-fat conditions, relative to high-carbohydrate
It was not clear whether carbohydrate-loading provides an additional benefit to ultra-endurance performance following high-fat conditioning
Diet had no significant effect on short-duration high-intensity performance, although a trend for impaired performance in the high-fat condition was attenuated with carbohydrate-loading
Further research is required to clarify if the trend for enhancement of ultra-endurance performance following high-fat diet is real.

Funding Source:

Industry:

Supro (New Zealand), PR Nutrition

Food Company:

University/Hospital:

University of Otago (New Zealand),

Reviewer Comments:

Inclusion and exclusion criteria not well-defined
Recruitment methods not specified
Food provided for subjects
Compliance monitored through diet diaries
Low precision from 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?		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?		N/A
	4.1.	Were follow-up methods described and the same for all groups?	N/A
	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%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	N/A
	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?	N/A
	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?	???
	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?	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