EAL

NAP: Training (2007)

Citation:

Van Zant RS, Conway JM, Seale JL. A moderate carbohydrate and fat diet does not impair strength performance in moderately-trained males. J Sports Med Phys Fitness. 2002; 42 (1): 31-37.

PubMed ID: 11832872

Study Design:

Randomized Controlled 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 three weeks of varied levels of dietary carbohydrate and fat intake on exercise training and high-intensity exercise performance in moderately strength-trained, aerobic-trained and untrained males.

Inclusion Criteria:

Subjects were either aerobically-trained (based on ACSM; exercised at least three times per week for 30 minutes at intensity of 50% to 85% maximum heart rate reserve for at least one year), strength-trained (based on ACSM; exercised at least three times per week for 60 minutes, incorporating a whole body workout, for at least one year) or sedentary (of normal weight, but no history of regular structured exercise within the last two years).

Exclusion Criteria:

More highly-trained athletes and cross-trained subjects were not selected.

Description of Study Protocol:

Recruitment: Methods not defined. Final subject selection based on similarity of training status, age, body weight and BMI.
Design: Randomized controlled crossover trial
Blinding used: Not used
Intervention: Isoenergetic diets considered either high-CHO low-fat or moderate-CHO moderate-fat for three weeks.

Statistical Analysis

ANOVA with repeated measures was used to evaluate the effects of training group, dietary treatment or the interaction of these main effects on exercise training and muscular strength and endurance
When significant main effects or interactions were identified, the least significant difference method was used to identify mean differences
Level of statistical significance was defined as P<0.05.

Data Collection Summary:

Timing of Measurements

Prior to the study and following each dietary treatment, muscular strength and endurance was determined
Six-week trials of all subjects were completed over seven months; subjects were tested in groups of six (two per group) across three seasons.

Dependent Variables

Muscular strength and endurance determined through isokinetic knee extension and flexion, single repetition maximum (one RM) concentric free weight bench press. Reported to lab after overnight fast.
Body composition determined through skinfold anthropometry, bioelectrical impedance analysis and body densitometry via underwater weighing
Maximum oxygen uptake via indirect calorimetry using a progressive cycle protocol
Exercise logs kept across six weeks of dietary treatment.

Independent Variables

Isoenergetic diets: High-CHO low-fat (62% CHO, 20% fat, 18% protein) or moderate-CHO moderate-fat (42% CHO, 40% fat, 18% protein) for three weeks
Food provided by Beltsville Human Study Facility, all food weighed
Dietary energy level estimated through equations
No washout period.

Description of Actual Data Sample:

Initial N

Six strength-trained
Six aerobically trained
Six sedentary subjects.

Attrition (Final N)

18 subjects as above.

Age

Aerobic: 32.2±8.7 years
Strength: 32.2±6.9 years
Sedentary: 32.0±3.9 years.

Ethnicity

Not mentioned.

Other Relevant Demographics

Aerobic body fat: 17.6±4.3%
Strength body fat: 17.0±4.8%
Sedentary body fat: 19.2±5.6%.

Anthropometrics

Similar in terms of training status, age, body weight and BMI.

Location

United States.

Summary of Results:

Other Findings

No differences as a result of the dietary treatment were seen in isokinetic peak torque, total work production, single-repetition maximum (one RM) bench press or number of bench press repetitions at 80% one RM
Self-reported exercise log data showed no dietary effect on the subject's ability to maintain training level.

Author Conclusion:

In summary, these findings indicate that prolonged (three-week) exposure to a weight maintenance, moderate CHO and fat diet, considered representative of a typical Western diet, does not impair muscular strength and high-intensity endurance exercise performance in moderately-trained (aerobic and strength) or sedentary males
Additionally, when compared to a high-CHO and low-fat diet, a moderate-CHO and fat diet did not impair the ability of strength- and aerobically-trained subjects to maintain their regular training over a three-week period
The significance of these results indicate that a wide range of dietary macronutrient intake is sufficient to meet muscular strength performance and training needs of the moderately-trained subject.

Funding Source:

Industry:

Ross Laboratories, Diagnostic Products Corporation

Food Company:

University/Hospital:

Northern Arizona University, Kent State University

Reviewer Comments:

Recruitment methods and inclusion and exclusion criteria were not well-defined
No wash-out 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?	???
	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?		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?	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?	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.)	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?	???
	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?		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