NAP: Energy Balance and Body Composition (2007)
Zachwieja JJ, Ezell DM, Cline AD, Ricketts JC, Vicknair PC, Schorle SM, Ryan DH. Short-term dietary energy restriction reduces lean body mass but not performance in physically active men and women. Int J Sports Med. 2001; 22: 310-316.PubMed ID: 11414677
- Men and women who regularly performed aerobic exercise
- All were healthy as determined by medical history and physical exam, including routine blood and urine chemistries.
- None had experienced significant weight loss or gain (over five kg) in previous six months
- None were routinely consuming dietary supplements such as creatine monohydrate.
- Recruitment: Recruitment methods not specified
- Design: Randomized controlled trial
- Blinding used: Subjects and primary investigators blinded to dietary treatment during intervention period
- Intervention: Subjects randomly assigned to either energy restriction for two weeks (N=16) or energy balance (N=8).
- Change from baseline was calculated for body composition, urinary nitrogen excretion and performance results and statistical differences were determined by an unpaired T-test
- To establish main effects, performance measures were also analyzed by repeated-measures ANOVA
- Body weight data were analyzed by repeated-measures using a mixed model with an unstructured covariance matrix.
Timing of Measurements
- 24-day study: 10-day baseline period followed by either two weeks of dietary energy restriction (750kcal per day, N=16) or energy balance (control, N=8)
- Pre- and post-intervention measurements of body composition, muscular strength and endurance, running performance, anaerobic capacity and urinary nitrogen excretion.
- Body weight determined each morning prior to breakfast, weighed on a calibrated electronic scale in street clothes after removing shoes, wallets, coins, keys from pockets, not allowed to weigh themselves during the intervention period
- Body composition measured by DEXA
- Muscle strength measured by leg and shoulder press, one repetition maximum
- Muscle endurance measured by leg squats to fatigue
- Running performance measured by five-mile run time
- Anaerobic capacity measured by Wingate anaerobic capacity test
- Urinary nitrogen excretion measured by chemiluminescence.
- Energy restriction (750kcal per day) for two weeks. Habitual energy and protein intake determined by three-day food record completed before study.
- Subjects were fed diets designed and prepared by metabolic kitchen
- Control diet: 51% CHO, 35% fat, 14% protein
- Energy restriction diet: 47% CHO, 34% fat, 19% protein
- Adjustments made for daily 500kcal per day treadmill exercise energy expenditure
- Subjects were interviewed for food allergies or intolerances
- Five-day cycle menu designed for all study participants.
- Initial N: 24 subjects, 13 men and 11 women
- Attrition (final N): 24, 16 in experimental group, eight controls
- Age: Mean, 24±4 years
- Ethnicity: Not mentioned.
Other Relevant Demographics
- Mean weight: 71.7±11.9kg
- Mean body fat: 22.9±7.8%
- Mean BMI: 24.1±2.8
- Mean VO2max: 51.5±5.0ml per kg per minute.
Differences between men and women described, but not between experimental and control groups.
Pennington Biomedical Research Center, Louisiana.
Results During Baseline and Following Intervention
|Lean Body Mass (kg)||51.9±1.8||51.1±2.7||55.7±4.1||55.6±3.9|
|Fat Mass (kg)||
|Nitrogen Excretion (grams per 24 hours)||10.4±1.0||13.2±1.0||10.6±1.0||11.2±1.0|
|Creatinine Excretion (grams per 24 hours)||1.56±0.12||1.54±0.11||1.48±0.06||1.59±0.13|
|Nitrogen / Creatinine (per 24 hours)||6.83±0.48||8.50±0.41||7.19±0.51||7.21±0.41|
|Muscle Endurance (repetitions)||73±16||88±19||69±10||95±29|
|Five-Mile Run Time (seconds)||2,566±72||2,380±54||2,612±88||2,475±77|
|Leg Muscle Strength (kg)||135.5±9.1||140.9±9.5||147.3±13.2||150.0±12.7|
|Shoulder Muscle Strength (kg)
Anaerobic Capacity (joules)
- Baseline energy intake was 3,151±118 kcal/day. Energy intake in the control group was constant averaging about 3,200 kcal per day and the restriction group consumed on average approximately 725kcal per day, compared to baseline (P<0.0001). Compliance to the intervention was high.
- Exercise energy expenditure averaged 470±6 kcal per day in all subjects, accomplished through treadmill running at a self-selected pace
- Body weight maintained in control group (-0.36±0.24kg), but energy restriction resulted in weight loss of -1.29±0.16kg (P<0.001). Gender had no influence.
- There was a trend for lean body mass to decline more in the energy restriction group (P=0.093), accounting for 61% of the weight loss. Urinary nitrogen excretion also tended to be higher in the energy restriction vs. control group (13.2±1.1 vs. 11.2±1.0g per day, P=0.089).
- Muscle strength was maintained or increased during the energy restriction period
- Muscle endurance improved following two weeks of energy restriction or balance
- Anaerobic capacity increased slightly in the restriction (+368±219 joules), but declined in the control group (-649±288 joules, P<0.05).
- The results of this study demonstrate that in exercising men and women, two weeks of moderate energy restriction does not impair skeletal muscle strength, endurance or five-mile run time and may even improve anaerobic capacity
- This implies that physically active men and women can become accustomed to, over the short-term, a moderate imbalance between energy intake and expenditure without sacrificing capacity to perform aerobic as well as anaerobic tasks
- However, energy restriction did result in modest weight loss, with a majority coming from the lean body mass compartment.
|Government:||Dept. of Defense|
- Experimental groups and control group not equally sized
- Differences between groups were not discussed
- Recruitment methods were not specified
- Inclusion criteria and exclusion criteria were not well-defined
- High dietary compliance to intervention through metabolic kitchen.
Quality Criteria Checklist: Primary Research
|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|
|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?||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?||???|
|3.1.||Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)||No|
|3.2.||Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?||???|
|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?||Yes|
|5.1.||In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?||Yes|
|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?||N/A|
|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)?||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|