NAP: Energy Balance and Body Composition (2014)


Paoli A, Grimaldi K, D'Agostino D, Denci L, Moro T, Bianco A, Palma, A. Ketongenic diet does not affect strength performance in elite artistic gymnasts. J Internat Soc Sports Nutr. 2012; 9: 34-43.

Study Design:
Non-Randomized Crossover Trial
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To investigate the influence of a very low carbohydrate ketogenic diet (VLCKD) on explosive strength performance.

Inclusion Criteria:
  • Male
  • Elite artistic gymnasts.
Exclusion Criteria:

Not described.

Description of Study Protocol:


Not described.


Non-randomized crossover (two experimental sessions with three-month wash-out period between sessions).


  • Very-low CHO ketogenic diet (VLCKD) for 30 days: 22g CHO (4.5% total energy), with 54.8% fat and 40.7% protein. A variety of speciality meals, principally of protein (18g per portion) and fiber, were provided. Three different herbal extracts and a multi-vitamin were taken with VLCKD.
  • Control diet for 30 days: Western diet with the exception of the fat being monounsaturated. Both diets were ad libitum and were individually explained by a qualified dietitian. 

Statistical Analysis

  • One-way ANOVA for repeated measurements
  • When appropriate, a Bonferroni post-hoc test was used to compare selected data. 
Data Collection Summary:

Timing of Measurements

Before and after 30 days on VLCKD and again before and after 30 days on Western diet (WD) after a three-month washout.

Dependent Variables

  • Body muscle and fat: Nine skinfolds, six bone circumferences, waist-and-hip circumferences using Standard Reference Manual
  • Weight: Electronic scale
  • Height: Stadiometer
  • Squat jump, counter-movement jump (CMJ) and 15 seconds of consecutive CMJs: Contact mat that allowed measurement of height of jump, time of flight and time of contact
  • Push-ups, reverse-grip chins test, legs closed barrier maximum test and parallel bar dips tests: Until exhaustion.
Independent Variables

Very-low CHO ketogenic diet and Western diet, both measured by three-day food diary.

Control Variables

Training was of similar intensity, volume and load.

Description of Actual Data Sample:
  • Initial NNine males
  • Attrition (final N): Eight
  • Age: 21±5.5 years
  • Ethnicity: Not described
  • Other relevant demographics: No significant differences in athletic performance

At baseline

  • Body weight: 69.6±7.3kg
  • Body fat: 7.6±1.4% 
  • Lean body mass: 64.2±6.5kg.

Padova, Italy.


Summary of Results:

Key Findings

  • While muscle mass and lean body mass post-VLCKD remained constant, there were significant differences in body weight (69.6±7.3kg to 68.0±7.5kg, P<0.05), fat mass (5.3±1.3kg to 3.4±0.8kg, P<0.001), fat percentage (7.6±1.4% to 5.0±0.9%, P<0.001) and lean mass percentage (92.4±1.44% to 95.0±1.0%, P<0.001) pre- and post-VLCKD.
  • There were no differences pre- and post-WD.  

Other Findings

  • There were no significant differences in anthropometric variables between the pre- and post-Western Diet
  • There were no significant differences in any performance tests either before and after VLCKD or WD. 
Author Conclusion:

Using VLCKD for a relatively short time (i.e., 30 days) can decrease body weight and body fat without negative effects on strength performance in high-level athletes.

Funding Source:
Gianluca Mech SpA, Orgiano, Italy
Food Company:
University/Hospital: University of Padova, National Technical University of Athens, Greece
Reviewer Comments:
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? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
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? 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? N/A
  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.) N/A
  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? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  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? N/A
  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