EAL

NAP: Training (2007)

Citation:

Lambert EV, Goedecke JH, van Zyl C, Murphy K, Hawley JA, Dennis SC, Noakes TD. High-fat diet vs. habitual diet prior to carbohydrate loading: effects on exercise metabolism and cycling performance. Int J Sport Nutr Exerc Metab. 2001; 11 (2): 209-225.

PubMed ID: 11402254

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 study the effects of a 10-day high-fat low-carbohydrate diet, followed by three days of carbohydrate-loading, on substrate utilization during constant-load, submaximal exercise and to determine the effects of such a diet on subsequent high-intensity cycling performance.

Inclusion Criteria:

Endurance-trained cyclists
Healthy
Had been cycling on a regular basis for more than three years
Consumed habitual diets that contained less than 40% fat.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Recruitment methods not described
Design: Randomized crossover trial
Blinding used: Not used; lab tests.
Intervention: High-fat diet or habitual diet for 10 days before ingestion of a high-carbohydrate diet for three days.

Statistical Analysis

It was estimated that the minimal sample size required to detect mean differences in fat oxidation during exercise was five persons per group with 80% power
Factorial ANOVA was used to compare differences between treatments over time
The Greenhouse-Geisser adjustment was used to correct for the maximal violation of the assumption of sphericity in this repeated-measures design
Where significant F-ratios were found, least squares post-hoc analysis was performed to determine differences at specific time points
Time trial performance was compared using a paired T-test with two-tailed P-values.

Data Collection Summary:

Timing of Measurements

Subjects consumed experimental diets for 10 days and high-carbohydrate diet for three days prior to testing, separated by a two-week washout period
Trials consisted of a 150-minute cycle at 70% VO_2peak, followed immediately by a 20-km time trial
Steady state gas exchange measurements for three to four minutes every 20 minutes during ride
Blood samples collected at rest and then after 40, 80, 100, 120, 120 and 140 minutes during the ride, at 160 minutes and then within one minute of completing the time trial.

Dependent Variables

Height and weight
Body composition through skinfold testing
Steady state gas exchange measurements
Blood samples analyzed for glucose, lactate, insulin, FFA, glycerol, beta-hydroxybutyrate, cholesterol and plasma 14C-glucose concentrations
Rate of plasma glucose oxidation determined through equation.

Independent Variables

High-fat (more than 65% fat) or habitual diet (30±5% fat) for 10 days
Three days of high-carbohydrate diet (more than 65% CHO)
One hour before each trial, cyclists ingested 400ml of a 3.44% MCT solution and during the trial ingested 600ml per hour of a 10%-14C-glucose + 3.44% MCT solution
Dietary intake assessed using three-day weight dietary record
Individualized menus were formulated for each subject and subjects were instructed to follow the diets to the best of their ability
Diets were designed to be isocaloric with 20% protein
Compliance indirectly confirmed by high initial rates of fat oxidation after high-fat diet.

Description of Actual Data Sample:

Initial N: Five subjects, all male
Attrition (final N): Five
Age: Mean, 22.4±1.5 years
Ethnicity: Not mentioned
Location: South Africa.

Summary of Results:

	Habitual Diet	High-Fat Diet	High-CHO Diet
Energy (MJ)	14.3±0.7	14.00	14.00
CHO percentage	52.6±5.8	<15%	>65%
Fat percentage	29.9±4.5	>65%	<15%
Protein percentage	12.8±0.9	20%	20%
Alcohol percentage	2.1±1.1

Other Findings

The dietary treatments did not alter the subjects' weight, body fat or lipid profile
There were also no changes in circulating glucose, lactate, FFA and beta-hydroxybutyrate concentrations during exercise
However, mean serum glycerol concentrations were significantly higher (P<0.01) in the high-fat diet
The high-fat diet increased total fat oxidation (P<0.05) and reduced total carbohydrate oxidation (P<0.01), but did not alter plasma glucose oxidation during exercise
The estimated rates of muscle glycogen and lactate oxidation were lower after the high-fat diet
The high-fat treatment was also associated with improved time trial times (29.35±1.25 minutes vs. 30.68±1.55 minutes for high-fat and habitual diet, respectively, P<0.05).

Author Conclusion:

In summary, results of this study suggest that dietary fat adaptation (10 days, fat above 65% energy) followed by carbohydrate-loading (three days, over 65% CHO) is associated with improved cycle time trial performance after prolonged constant-load exercise
These data provide some evidence that nutritional periodization may be a useful strategy for prolonged endurance performance and that high-fat feeding prior to carbohydrate-loading may result in persistent adaptations favoring fat oxidation and sparing of endogenous carbohydrate, even during high-intensity exercise.

Funding Source:

Government:	Medical Research Council of South Africa
University/Hospital:	University of Capetown

Reviewer Comments:

Dietary compliance not directly checked; authors note that if subjects did not adhere to diets, the effects may have been underestimated
Recruitment methods not described
Authors note that lack of blinding may have resulted in motivational factors associated with the diet on performance.

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?		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?		No
	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?		???
	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?	No
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	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?	Yes
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