EAL

NAP: Training (2007)

Citation:

Horvath PJ, Eagen CK, Fisher NM, Leddy JJ, Pendergast DR. The effects of varying dietary fat on performance and metabolism in trained male and female runners. J Am Coll Nutr. 2000; 19 (1): 52-60.

PubMed ID: 10682876

Study Design:

Non-Controlled Trial

Class:

D - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To determine if increasing dietary fat intake from the low levels (about 15% of daily calories) typical of runners to higher levels (about 45% of daily calories), while maintaining adequate levels of carbohydrates, increased VO_2max and endurance time, as well as to investigate the potential mechanisms involved.

Inclusion Criteria:

Runners running a minimum of 35 miles per week, healthy, non-smoking, between ages of 18 and 55 years.

Exclusion Criteria:

Excluded if not included above.

Description of Study Protocol:

Recruitment: 1,300 runners from the greater Buffalo metropolitan area running community were sent letters requesting their participation in the study.
Design: Non-randomized clinical trial
Blinding used: Not used.
Intervention: Subjects consumed diets of 16%, 31% or 44% fat for four weeks.

Statistical Analysis

Comparisons were made using all 25 subjects between the first two diets and using 12 subjects between the last two diets
Two-way ANOVA with repeated measures was used with diet and gender as the main factors for all performance data
For blood measurements, a three-way ANOVA with repeated measures was done using diet, gender and time during the exercise test as the main factors
The effects of low- to medium-fat diets were analyzed with N=25 and the medium- to high-fat diets analyzed with N=12
Post-hoc testing to determine significant difference among the means was done using the Newman-Kuels post-hoc test (P<0.05).

Data Collection Summary:

Timing of Measurements

Endurance and VO_2max tested at the end of each diet
Blood sampled before and after the VO_2max and endurance runs.

Dependent Variables

Endurance; run to exhaustion at 80% of VO_2max
Wingate Anaerobic Power Test
VO_2max measured through expired gas collection
Plasma levels of lactate, pyruvate, glucose, glycerol and triglycerides measured by colorimetric commercial kits
Free fatty acids assayed using spectrophotometric method
Body weight measured on electronic scale
Body fat percentage measured by underwater densitometry.

Independent Variables

Isocaloric diets of 16%, 31% or 44% fat for four weeks
Given one-week sample menus to follow, but food was self-selected
Subjects taught how to record their food, fluid and supplement intake and returned food records weekly to dietitians for review to determine compliance
No washout period.

Description of Actual Data Sample:

Initial N: 45 subjects originally met the criteria to participate, but it is unclear how many enrolled.
Attrition (final N): 25 subjects completed the study; 12 males and 13 females completed the first two diet periods and six males and six females completed all three diet periods

Age

Females: 33±2.2 years for LF-MF, 32±3.2 for MF-HF
Males: 37±2.0 for LF-MF, 36±2.6 for MF-HF.

Ethnicity

Not mentioned.

Anthropometrics

Males and females were significantly different from each other in terms of height, weight, body fat and VO_2max.

Location

Buffalo, New York.

Summary of Results:

Measurements During the Endurance Run

	Time (Minutes)	Maximum Heart Rate (BPM)	R
Female; 16% fat	39.23±11.23	162.5±2.6	0.94±0.01
Female; 31% fat	46.61±13.46	163.7±2.5	0.96±0.01
Male; 16% fat	44.32±9.55	164.4±2.7	0.96±0.01
Male; 31% fat	54.94±12.84	159.7±2.8	0.97±0.01
Female; 33% fat	47.22±11.64	160.5±4.3	0.96±0.01
Female; 44% fat	48.17±15.28	164.8±4.2	0.96±0.01
Male; 33% fat	47.08±10.07	160.0±3.4	0.97±0.02
Male; 44% fat	48.49±11.64	160.0±2.4	0.95±0.02

Other Findings

Runners on the low-fat diet ate 19% fewer calories than on the medium- or high-fat diets
Fat levels actually consumed by runners were 16% and 31% for 25 subjects used on low- to medium-fat diet comparisons and 33% and 44% for 12 subjects used for medium- and high-fat comparisons
Body weight, body fat percentage, VO_2max and anaerobic power were not affected by the level of dietary fat
Endurance time increased from the low-fat to medium-fat diet by 14% (increased 20% in females and 8% in males). There were no significant differences between the high- and medium-fat diets.
No differences were seen in plasma lactate, glucose, glycerol, triglycerides and fatty acids, when comparing the low- vs. the medium-fat diet
Subjects who increased dietary fat to 44% had higher plasma pyruvate (46%) and lower lactate levels (39%) after the endurance run.

Author Conclusion:

These data support previous studies demonstrating that increased dietary fat intake, without compromising carbohydrate intake, improves endurance performance
If the diet is hypocaloric however, increasing fat and decreasing carbohydrates reduces glycogen stores and impairs performance
Clearly demonstrated by the reduced running capacity on the low-fat diet, reduction in total calories or fat is not conducive to optimal exercise performance
It is suggested that the intramuscular stores of glycogen and fats are the crucial ones as the rate of supply from the blood is too slow to meet energy requirements
The blood substrates are important for the replenishment of intramuscular stores during recovery from exercise
The present study extends these observations to female runners and runners of a more recreational nature
The present study does not support the hypothesis that increasing fat to 44% of total calories improves performance to a greater extent than does 31% fat. However, further studies using more intensely trained athletes with lower body fat are needed.

Funding Source:

Industry:

Mars Inc.

Food Company:

Reviewer Comments:

Compliance assessed by dietitian review, but subjects did not follow diets well and only half of subjects increased fat intake to 44%
Unclear as to how many of 45 subjects asked to participate actually enrolled
No washout period between diets.

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?	Yes
	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?		???
	4.1.	Were follow-up methods described and the same for all groups?	???
	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%.)	???
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	???
	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?		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.)	No
	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)?	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?	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