Energy Expenditure

Energy Expenditure (EE): Glossary (2005)

Glossary of Terms

Adjusted body weight

Can be calculated by the following formula:   Adjusted wt (kg) = [(actual body wt – ideal wt) X 0.25] + ideal wt

Age classifications

        Adults – Definition is different from Medical Subject Heading (MeSH) “adult” and will represent persons, ages 19 – 79 years.

        Young, Middle-aged or Older adults –These are general descriptive terms that reflect a particular study population and when used will report the age range or mean plus/minus standard deviation of the particular study so identified.  Specific descriptive terms that are used in the evidence summary are defined below:

        Young-old adults will represent individuals 65-74 years

        Old adults will represent individuals 75-84 years

        Oldest old adults will represent individuals 85 years and older

        Older adults-is a general description of an aging population and this term will represent studies that identified persons ages 65 years and older as a dominant characteristic of the population (or a group within a sample) studied.

        Aged is defined under the MeSH term “Aged” and indicates 65-79 years

        Oldest Old is reflected under the MeSH term “Aged, 80 and older.  However, in this project “Oldest old adults” will represent individuals 85 years and older.

Basal energy expenditure (BEE) or Basal metabolism rate (BMR)

BMR is the minimal energy requirement to sustain vital functions during absolute rest.  BMR includes the energy expended in ventilation, blood circulation, intestinal contraction, the activities of internal organs, and the maintenance of thermal equilibrium.  Controlled measurements of BMR are taken in early morning, within 30 minutes of waking, before eating, and before any physical activity are undertaken.  The person should be lying flat on his or her back.

Client compliance 

This is defined as a change in motivation and/or ability for an individual to make dietary change because of a perceived benefit of actual, individualized energy measurements.

Coefficient of variation

A statistical measurement that compares variability in samples from populations with different means.  It is a proportion of the standard deviation divided by group mean multiplied by 100 to translate into a percent:  The mathematical formula is:

                               Standard deviation/ ´ * 100

Design Quality

Studies identified as “high quality” or “strong design” (i.e., a “plus” quality rating) had to identify or discuss individual characteristics of weight and age since both are intervening variables that are on the pathway that determines accuracy of measured or predicted RMR.  In addition, diseases allowed or excluded needed to be identified since certain diseases are associated with metabolic rate variations.  Studies had to address indirect calorimeter protocol adherence in the following areas:

1)     machine calibration

2)     20-30 minute rest before measurement if traveling to a measurement center or to discuss procedures prior to single measurements (e.g., machine acclimation measurements)

3)     steady state (e.g., pre-determined group mean covariance, elimination of erratic measurements and/or ongoing monitoring; depending on study discussions reporting “adherence to study protocol” was potentially eligible)

4)     measurement length

5)     exercise restrictions in healthy adults the day prior to measurements or identifying/monitoring movement restrictions/restlessness in critically ill patients

6)     fasting (ideally, specifying fasting length > 8 hrs but accepted “overnight”) with an exception for studies including patients on IV, parenteral or enteral feedings.

Because of the health ranges of the populations studied, evidence analysts had difficulty distinguishing certain aspects of initial steady state measures and any ongoing monitoring that occurred but may have been unreported in the written study description.  Thus, mentioning steady state qualified as meeting this criterion in the methodologically-sound protocol evaluation.  In addition, an exception to the exercise criterion was given to studies measuring energy expenditure in older adults because of a reduced likelihood of participating in significant physical activity the day prior to an energy expenditure measurement.  All studies evaluated reported a procedure that excluded subjects taking “medications that affect metabolic rate” or identified stability in post-menopausal women using hormone therapy.

Dietary thermogenesis (also known as specific dynamic action, thermic effect of food, or specific effect of food)

An increase in metabolic rate due to the digestion, absorption, transport, metabolism, and storage of energy from ingested food, digestion and metabolism of exogenous nutrients.  This is estimated to be approximately 5-15% above RMR.  The thermic effect of food is transient and peaks at approximately 7% above RMR within the first hour after a light meal and returns to baseline over the next hour.

Expected years of life lost

The difference between the number of years a person would be expected to live if he/she was not obese and the number of years expected to live if the person were obese.

Respiratory Exchange Ratio (RER)

The ratio of CO2 elimination of O2 uptake and reflects the net substrate utilization of the individual at rest and also during physical activity of low or moderate intensity.

Respiratory Quotient (RQ)

The ratio of CO2 elimination of O2 uptake and reflects the net substrate utilization of the individual   in throughout the range of physiological states, resting through extreme activity.  It is used in exercise testing to mark the point at which VO2 no longer rises, but VCO2 does and the RER rises.

Resting metabolic rate (RMR) or Resting energy expenditure (REE)

RMR is measured after 30 minutes of recumbent rest, preferably but not necessarily early in the morning; with as little physical activity as possible before the measurement.  RMR is the sum of the metabolic processes of active cell mass related to the maintenance of normal body functions and regulatory balance during rest.  This includes any heightened metabolic activity due to prior physical, mental or stress-related activities.  The subject should be in a fasted or post-prandial state.

Single measurement

An average of consecutive data points recorded by a machine (the measurement length and number of data points included in each single measurement may vary by instrumentation and protocol).

Steady state

A predetermined criterion that defines a minimumVO2 from one minute to the next.  Some calorimeters use artifact suppression to eliminate erroneous data.

Statistics

The differences between measured and predicted resting metabolic rate (RMR) can be reported with various statistics.  Some statistics evaluate the difference between predicted and measured RMR at one point in time; other statistics are concerned with the difference between predicted and measured RMR changes over time. Additionally, some studies use statistics to report how the measured RMR of groups of people differ from the predicted rate, whereas other studies are concerned with how the measured RMR of individuals in a particular group will differ from the predicted RMR.  Simplified ways in which studies have represented the differences between predicted and measured RMRs are discussed.

                These notations are used in the equation discussions of that follow:
                                                Mg is the measured group average RMR
                                                Mi is the measured individual RMR
                                                Prmr is the predicted RMR

Absolute Simple Differences

Group

Individual

Mg- Prmr or Prmr -Mg

 

Mi- Prmr or Prmr -Mi

 

Absolute Simple Differences

Reporting absolute differences between measured and predicted metabolic rates provides information about the measurement range of differences (i.e., overestimates and underestimates).  When reporting RMR, the difference is translated into kcals/d.

An absolute simple individual difference is calculated by subtracting one amount from the other (see below).

A statistical approach that reports group mean prediction error uses a Student’s t-test to identify the bias (i.e., the accuracy of each individual’s prediction) and gives a standard deviation (i.e., the absolute precision or consistency of the difference).  This represents an estimate of how far off any given member of a group’s estimated energy needs will be.  This approach averages overestimates and underestimates.  Thus, individual factors influencing over- and under-prediction errors (e.g., group member characteristics, conditions of how RMR was measured) are important to understand when comparing group mean prediction errors.

Individual

Group

Mi- Prmr (ind) or Prmr (ind) -Mi

Mg- Prmr (group) or Prmr (group) -Mg

 

95% Limits of agreement analysis (or 95% Probability of Individuals within a Reference Interval) represents a reference interval for individual resting metabolic rate differences (measured and predicted) and identifies the 95% expected probability that new individuals selected from a similar population would have difference scores (i.e., measured minus prediction) within the limits of agreement range.  Sample sizes of at least 50 individuals are needed in a study for the sample limits of agreement to be precise.

Relative Error Differences (Proportions) and Percents

Relative measures allow comparisons without regard to the magnitude of the measurement range yet these measures give information about the importance of the error.  This type of measure is a proportion because the observation of the difference between two measures in an individual (or group mean measures) that are reported in the numerator is linked to the denominator by a measure of the same individual or group at a certain time point.

A relative error difference of predicted RMR from measured RMR gives significance about the magnitude of the error within an individual or compared to a group of individuals with different RMRs.  For example, a 200-kcal/day error may be less important in a healthy subject who requires 2,700 kcals/d  (i.e., a proportion of 200 kcals /2,700 kcals) whereas this error becomes more important if it occurred in someone on an 800-kcal/day weight reduction diet (i.e., a proportion of 200 kcals /800 kcals).

Relative errors are sometimes expressed as percentages.  To convert a relative error into a percentage error, multiply by 100.  In the healthy subject described above, the relative error would be approximately 7% of total daily kcalories whereas the error for the individual on an 800-kcals diet would be 25%.

Individual

Group

(Mi- Prmr (individual)) / Prmr (individual)

 

(Mi- Prmr (individual)) / Mg  

 

 (Mi- Prmr (individual)) / Prmr (individual) *100

 

(Mi- Prmr (individual)) / Mg *100

 

 (Mg- Prmr (group)) / Prmr (group)

 

(Mg- Prmr (group)) / Mg

 

 (Mg- Prmr (group)) / Prmr *100

 

(Mg- Prmr (group)) / Mg * 100

 

In summary it is important to distinguish between the following characteristics:

·         Is the measured group RMR or the measured individual RMR the main concern?

·         Is the divisor the measured group RMR or the predicted RMR?

·         Researchers determine how to analyze the data based on whether they want to evaluate the accuracy of a predictive equation or the accuracy of a measurement and whether they want to apply the results to individuals or a population (i.e., groups of individuals).  Careful analyses of these differences are needed when reviewing the evidence analysis worksheets. 

Relative Ratio

A ratio is the value obtained by dividing one quantity by another and the numerator and denominator do not have to be mutually exclusive.  Measured individual RMR is divided by predicted RMR of that individual or a measured group mean RMR can be divided by the predicted group mean RMR.  In evaluating measured to predicted ratios in groups, this is reported as “mean to prediction ratio” (or percent mean to prediction ratio if multiplied by 100). 

Individual

Group Difference

Mi / Prmr (individual) or Mi / Mg

Mg / Prmr (group) or Prmr (group) / Mg

Root-mean squared prediction error (RMSPE)

An analysis that determines how close the predicted RMR value for each individual is to the actual measured RMR.  This approach more accurately presents the accuracy of the prediction equation for each person (i.e., individual prediction error bias), rather than as a mean of the entire sample since the absolute error (or root mean squared error) eliminates the influence of negative or positive signs of over- or under-prediction within individuals.  Thus, this approach more accurately reflects individual over- and under-estimations.

Study Sampling Exclusion Criteria

Illnesses excluded from studies in this section were patients with restlessness or agitation at the beginning of IC, those with inspiratory oxygen greater than 0.60, those with an air leak via chest tubes or ventilator circuits, and those with a positive end-expiratory pressure >20 mm Hg.

Total energy expenditure (TEE)

The energy expended for basal metabolic rate, diet-induced thermogenesis, and energy expended for activity over a 24-hour period. 

Weight Classifications

The indirect calorimetry study integrated the BMI classification distinctions between Overweight and Obesity.  Healthy adults included healthy (i.e., “normal”) weights and overweight BMI classifications.  Obese adults included individuals with BMIs >/= 30 kg/m2

 

Classification of Overweight and Obesity by BMI*

 

BMI (kg/m2)

Obesity Class

Underweight

<18.5

 

Normal

18.5-24.9

 

Overweight

25.0 – 29.9

 

Obesity

30.0 – 34.9

I

 

35.0 – 39.9

II

Extreme Obesity

>/= 40

III

*National Heart, Lung, and Blood Institute.  NHLBI Obesity Education Initiative Expert Panel. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults.  The evidence report.  Bethesda, MD: National Institutes of Health, National Heart, Lung, and Blood Institute (NHLBI), June, 1998.

Classification of Overweight and Obesity by Percent Body Fat

Body Fat Guidelines from the American Dietetic Association and DRI Prepublication

 

American Dietetic Association

Institute of Medicine. Dietary Reference Intakes

Classification

Women
(% Fat)

Men
(% Fat)

Women
(% Fat)

Men
(% Fat)

Normal

(BMI 18.5 up to 25)

15-25

10-20

23-31

13-21

Overweight

(BMI 25 up to 30)

25.1-29.9

20.1-24.4

31-37

21-25

Obese

(BMI 30 up to 35)

> 30

> 25

37-42

25-31

Clinically obese

(BMI 35 or >)

 

 

>31

>42

Gallagher D, Heymsfield SB, Geo M, Jebb SA, Murgatroyd PR, Sakamoto Y.  Healthy percentage body fat ranges: an approach for developing guideline based on body mass index.  Am J Clin Nutr. 2000;72:694-701; Institute of Medicine.  Dietary reference intakes: energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids.  Washington, DC: National Academy Press. 2002; Internet access:  http://www.nap.edu/books/0309085373 , Accessed February 20, 2003.