• Increase Font Size
  • Decrease Font Size
  • View as PDF

EE: Application of RQ (2005)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To present the recent developments in the assessment of energy expenditure and fuel utilization in man.
Inclusion Criteria:
Criteria for article inclusion not specified.
Exclusion Criteria:
Criteria for article exclusion not specified.
Description of Study Protocol:
  • Search procedures: not specified
  • Was study quality assessed? No
Data Collection Summary:

Outcome(s) and other measures

  • VO2, VCO2, RQ and how the measure reflects physiological oxidation of nutrient substrates.
Description of Actual Data Sample:
  • # 41 articles included
  • # of articles identified not specified
  • 17 of 41(41%) articles were before 1980
  • Three animal studies are used to present a potential RQ >1 during fat deposition.
  • Sample size of studies, and characteristics of the study participants.
Summary of Results:

Indirect calorimetry has the advantage of a small response time, whereas direct calorimetry gives a delayed response; Oxygen consumption follows ATP production on line and is directly related to the subject’s energy expenditure.

DIRECT CALORIMETRY

  • [Information is not abstracted for the RQ question]

INDIRECT CALORIMETRY WITH RESPIRATION CHAMBER

It is important to take into account in the calculation of VO2 that the flow rate at the inlet is different from that of the outlet; this is because CO2 production rate (VCO2) is usually smaller than the O2 consumption (VO2). Thus, using Haldane’s correction, VO2 is obtained using an equation.

FUEL UTLIZATION IN MAN

By measuring VO2 consumption and CO2 production, and urinary nitrogen excretion, it is possible to calculate overall substrte oxidation. However, these data give no information about the substrates being oxidized in individual organs and tissues.

THEORETICAL LIMITATIONS

  • (Unable to abstract as missing page)

PHYSIOLOGICAL CONSIDERATIONS

Assumptions made:

  1. The urea pool and the bicarbonate pool remain stable or in equilibrium.

Hyperventilation example
During hyperventilation carbon dioxide is eliminated in excess of that produced by oxidative metabolism and there is a decrease in the bicarbonate pool. CO2 elimination increases rapidly and exceeds concomitant O2 consumption: this results in a RQ>1.00. The period of hyperventilation is followed by a compensatory period of hypoventilation during which metabolically produced CO2 is stored to re-equilibrate the bicarbonate pool. Provided that the respiratory exchange measurements encompass these transient changes, the mean values for CHO and fat oxidation will be correct. Since VO2 changed very little during hyperventilation, the calculated energy expenditure is not greatly affected.

SPECIFIC SITUATIONS WHERE RQ IS OUTSIDE OF RANGE

RQs<0.7

  1. Starvation
  2. Individuals receiving high-fat, low-carbohydrate hypocaloric diets,
  3. Alcoholics, and diabetes in the postabsorptive state.
  4. An increase in substrate flux through metabolic pathways that have low RQs, e.g., gluconeogenesis and ketogenesis

RQs>1

  1. Net synthesis of fat from CHO (primarily measured in animals); but theimportance of net lipogenesis in human nutrition is less evident.

[Sources: Passmore R, Strong J et al, 1963. The effect of overfeeding on two fat young women. Br J Nutr, 1963; Passmore R, Swindells YE. Observations on the respiratory quotients and weight gain of man after eating large quanities of carbohydrate. Br J Nutr, 1963]

NONCALORIMETRIC METHODS WITH REFERENCE TO 2H218O TECHNIQUE

  • Not abstracted
Author Conclusion:

As stated by the author in body of report

The equations to calculate M (dot) that is measured by indirect calorimetry and represents the rate of heat production i.e., Weir’s equation or the equation based on the nonprotein respiratory quotient, are valid even in the presence of lipogenesis from carbohydrates or gluconeogenesis.

Funding Source:
University/Hospital: University of Lausanne
Reviewer Comments:

A nice report and discussion on identifying the three areas related to RQ accuracy: theoretical limitations, physiological considerations, and specific clinical situations.

 

Weaknesses include use of older studies and presenting RQ data on animals to introduce theory of an RQ >1 during net lipogenesis. However, author does discuss the limitations.

Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? No
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? No
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? No
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? No
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? No
  10. Was bias due to the review's funding or sponsorship unlikely? Yes