EE: Respiratory Quotient (RQ) (2014)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To compare the acute, energy-cost of meal-induced thermogenesis on a high-protein, low-fat diet vs. a high-carbohydrate, low-fat diet.



Inclusion Criteria:
  • Understand and give written consent
  • Healthy female nonsmokers
  • Regular menstrual cycle
  • Take no prescription medication.
Exclusion Criteria:
  • Refusal to consent
  • Not meeting inclusion criteria
  • Diseases in subjects that were excluded: Renal or hepatic disease, DM, heart disease, hypertension.
Description of Study Protocol:


Subjects were recruited from a campus population.


Randomized, crossover trial.

Statistical Analysis:

  • One-tailed, paired T-tests were used to analyze differences between blood and urine indices
  • Multiple analyses of variances for repeated measures with appropriate post-hoc tests used to evaluate differences between mean post-meal values for thermogenesis, non-protein RQ and body temperatures
  • Pearson correlation used to assess relationships between variables.
Data Collection Summary:

Timing of Measurements

  • Using a randomized, cross-over design, subjects consumed the high-protein (HP) and the high-carbohydrate (HC) diets for one day each
  • Testing was separated by a 28- or 56-day interval
  • Control diets were consumed for two days prior to each test day
  • On test day, REE, RQ, and body temperature were measured following a 10-hour fast and at 2.5 hour post breakfast, lunch and dinner
    • Lunch was provided four hours after breakfast; consumed within 15-minute interval
    • Dinner was provided four hours after lunch
  • 24-hour urine collections were provided on day of testing.

Dependent Variables

  • Measured REE [(VO2 L per minute), VCO2 (L per minute; ml per kg per minute), RQ, ventilation (L per minute)]
    • IC type: MAX-1 metabolic cart
    • Equipment of Calibration: Not addressed
    • Coefficient of variation using std gases: Yes
    • Rest before measure (state length of time rested if available): 30 minutes
    • Measurement length: 20 minutes
    • Steady state: Not addressed
    • Fasting length: 10 hours
    • Exercise restrictions XX hour prior to test? No
    • Room temp: 25°C to 27°C
    • Number of measures within the measurement period: Continuous measurements within 20-minute period
    • Were some measures eliminated? No
    • Were a set of measurements averaged? Yes; a mean of 20-minute continuous measurements were used to estimate resting REE
    • Number of measurements: Four
    • Length of measurements: 15
    • RQ: Calculated by standard formula
    • Coefficient of variation in subjects measures? No
    • Training of measurer? Not addressed
    • Subject training of measuring process? Not addressed
    • Monitored heart rate? No
    • Body temperature? Yes
    • Medications administered? No
  • Blood and urine chemistries:
    • Plasma insulin: Immunoradiometric assay
    • Plasma and urine urea nitrogen, plasma and urinary creatitine calorimetrically
    • Apparent nitrogen balance: Calculated as the difference between total dietary nitrogen and total urine nitrogen (urine urea nitrogen x 1.25) with a correction of 1.8g nitrogen loss daily to account for obligatory and fecal losses
    • Glomerular filtration rates (GFR): [Urine creatinine (mg per dL) x urine volume (ml)]/[plasma creatinine (mg per dL) x minutes].

Independent Variables

  • Diet composition: Energy content determined for individual subjects using the Harris-Benedict equation BMR estimate x 1.3
    • Control or high CHO diet (HC)
      • 50% complex CHO
      • 10% simple sugar
      • 15% protein
      • 25% fat
    • High Protein diet (HP)
      • 30% complex CHO
      • 10% simple sugar
      • 30% protein
      • 30% fat.

Control Variables

Testing was separated by a 28- or 56-day interval to control for possible confounding effects of menstrual cycle.

Description of Actual Data Sample:
  • Final N: 10 healthy females
  • Age:  19.0±0.4 years (range: 18-22)
  • Anthropometrics:
  Mean ± SEM Range
Height (m) 1.66±0.01 1.59 to 1.74
Weight (kg) 64.4±2.4 55.0 to 77.3
BMI (kg/m2) 23.4±0.9 18.6 to 28.4
Body fat (%) 25.2±2.3 13.9 to 26.1
  •  Location: Arizona State University, US.


Summary of Results:


  • Fasting REE was similar prior to the diet intervention for HC and HP
  • Post-prandial REE was 8.0kcal per hour higher at 2.5 hours following the breakfast meal (P<0.05), and 8.0kcal per hour higher at 2.5 hours following the lunch meal (not significant) on HP diet vs. the HC diet
  • At 2.5 hours after the dinner meal, post-prandial REE was 14kcal per hour higher on the HP diet compared to the HC diet (P<0.05).

Non-protein RQ

  • The fasting non-protein RQ was similar prior to diet intervention 0.81±0.01 and 0.79±0.02 for high CHO and high protein diets, respectively
  • Assuming normality, 98% of individual fell within two SD or [0.01 X v10 =0.032] X 2=0.060, or RQ range 0.75 to 0.87 for high protein diet
  • [0.02 x v10=0.06] x 2=0.13, or RQ range 0.66 to 0.92 for high CHO diet
  • Changes in non-protein RQ measured at 2.5-hour post-meal did not differ by diet
  • High CHO 2.5-hour, post-prandial, non-protein group mean RQ changes for breakfast, lunch and dinner, respectively were 0.035 breakfast, 0.02 lunch, and 0.05 dinner
  • High protein 2.5-hour, post-prandial RQ group mean changes for breakfast, lunch and dinner, respectively were 0.025 at breakfast, 0.052 at lunch, and 0.06 at dinner.

Other Results

  • Changes in body temperature were not significantly different by diet
  • Fasting plasma insulin concentrations before and after the diet intervention did not vary by diet
  • Fasting plasma urea nitrogen concentrations were similar prior to diet intervention for HC and HP. At 24 hours post-intervention, fasting plasma urea nitrogen concentrations were raised (P=0.05) on the HP diet vs. the HC diet
  • GRF did not vary by diet treatment
  • Nitrogen balance was significantly greater on the HP diet (+7.6±0.9gN per day) compared to the HC diet (-0.4±0.5gN per day) (P<0.05).


Author Conclusion:
  • These data demonstrated that meal-induced thermogenesis at 2.5 hour post-meal averages about twofold high on a HP low-fat diet  vs. a HC, low-fat diet
  • Postprandial thermogenesis on the HP diet totaled 30 more kcal at 2.5 hours post-meals. If the same energy differential was maintained for two- to three-hour intervals post-meals, the added post-prandial thermogenesis associated with the HP diet may have been as high as 90kcal.
  • These data indicate an added energy-cost associated with high-protein, low-fat diets and may help explain the efficacy of such diet for weight loss.
Funding Source:
University/Hospital: Arizona State University
Reviewer Comments:


  • Good study design; care was taken on the dietary protocol to reduce the effects of possible confounding factors
  • Sophisticated statistics
  • Randomization of treatment were performed.


  • Relatively small sample size (N=10). Only applied to healthy young women. Results may be different on athletes, men or the elderly.
  • Only assesses the acute effects of the diets on energy expenditure. Compared with high CHO diet, the intensity of the effects on high PRO diet on energy expenditure may be less in a long run.
  • Agree with the following statement, “The data presented here further demonstrated that an acute change in dietary protein, 15% to 30 % of dietary energy, had little effect on renal function in healthy individuals.” However, long-term effects on the high protein diet may have adverse effects on renal functions. Thus, to promote long-term use of high-protein diet for weight loss purpose should be further evaluated.

Implications to IC questions

Compared to high carbohydrate diet, high protein diet prior to the 2.5 hour increased REE.

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? N/A
  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.) 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? No
  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%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? ???
  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.) 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? Yes
  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? 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? ???
  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