Resting Energy Expenditure "REE"
By Denise Schwartz, MS, RD, FADA, CNSD
What does REE mean?
Resting energy expenditure represents the amount of calories required
for a 24-hour period by the body during a non-active period. Energy
expenditure can be estimated by numerous published formulas. There are
nearly 200 published energy expenditure formulas dealing with various
conditions, disease states, age, presence of obesity and other
additional factors. (5) One of the most frequently used formulas for
predicted energy expenditure are the Harris-Benedict equations. These
were established in 1919 and took into account gender, age, height and
weight. However, these formulas are skewed towards young and non-obese
Harris-Benedict Equations (calories/day):
Male: (66.5 + 13.8 X weight) + (5.0 X height) - (6.8 X age)
Female: (665.1 + 9.6 X weight) + (1.8 X height) - (4.7 X age)
weight in kilograms, height in centimeters, age in years
The Harris-Benedict equations have been found to overestimate by 6% to
15% the actual energy expenditure measurements done by indirect
calorimetry. (3) There is a large variation between individuals, when
comparing their measured energy expenditure to the calculated amount.
These equations have limited clinical value when tailoring nutrition
programs for specific individuals for weight loss purposes or acute as
well as chronic illness feeding regimens.
Energy expenditure can be measured directly by putting a person in a
calorimeter and measuring the amount of heat produced by the body mass.
This is expensive and very impractical in the clinical setting. Energy
expenditure can be measured indirectly with a metabolic cart by
analysis of respired gases (usually expired) to derive volume of air
passing through the lungs, the amount of oxygen extracted from it
(i.e., oxygen uptake VO2) and the amount of carbon dioxide,
as a by-product of metabolism, expelled to atmosphere (CO2 output â€“ VCO2)
â€“ all computed to represent values corresponding to 1 minute time intervals.
With these measurements the resting energy expenditure (REE) and respiratory quotient (RQ) can be calculated.
The RQ represents the ratio of carbon dioxide exhaled to
the amount of oxygen consumed by the individual. RQ is useful in
interpreting the results of the REE. The abbreviated Weir equation is
used to calculate the 24-hour energy expenditure. These measurements
are printed out by the metabolic cart after completion of the indirect
calorimetry test. (1,4,5)
Abbreviated Weir Equation:
REE = [3.9 (VO2) + 1.1 (VCO2)] 1.44
VO2 = oxygen uptake (ml/min)
VCO2 = carbon dioxide output (ml/min)
Respiratory quotient (RQ) = VCO2/VO2
Benefits of using REE in the clinical setting
The REE is useful to prevent under and overfeeding of individuals,
especially in the acute care hospital setting. Excessive calories or inadequate feeding regimens can have detrimental effects on clinical outcomes of patients' care. Malnutrition can result from feeding a patient less than his/her metabolic requirements leading to reduced respiratory muscle strength, increased risk of infection, poor wound healing and impaired normal body function. Overfeeding means providing too many calories that can not be used by the body and are therefore converted to fat storage.
This can cause more CO2 to be produced and result in increased work of breathing. The REE measurement is especially beneficial in the ventilator dependent patient population during the process of weaning
the individual from mechanical ventilation to resume (reestablish) spontaneous breathing. (7)
How do you do the test?
For best results, when having a REE done, there are certain conditions
that need to be controlled and others that just require documenting
at the time of the test. During the test the individual is interfaced with a
metabolic measurement system by means of a facemask or a canopy.
A mouthpiece with a nose clip is also sometimes used, but it may create
overly stressful conditions to a subject (patient).
Important considerations or conditions to improve the REE measurement:
- Individual should rest for at least 30 minutes in bed or a
recliner before the test, however, the person should not be asleep.
- No food for at least 2 hours before the test.
- Maintain quiet surroundings when the test is in progress and normal temperature. The individual should not move arms or legs during the test.
- Normal room temperature should be maintained, avoid drafts or any condition that might result in shivering.
- Medications taken should be noted, such as stimulants or
- Steady state should be achieved, which would be identified
clinically by the following:
5 minute period when average minute VO2 and VCO2
changes by less than 10% and the average RQ changes
by less than 5%.
Stable interpretable measurements should be obtained in a 15 to 20
Additional considerations for hospitalized individuals:
- If the individual is on specialized nutrition support (enteral or
parenteral nutrition) continuous 24-hour infusion does not need
to be stopped. The nutrients infused should be constant for at
least 12 hours. If feedings are intermittent or cyclic, the feeding
should be held for at least 2 hours. Document the product and
the rate the individual is receiving.
- Discontinue any supplemental sources of oxygen if the individual is on room air, which includes nasal cannulas, masks or tracheostomy collars.
- If the individual is on a ventilator, the settings should remain
constant for at least 1-1/2 hours before the test.
- No recent chest therapy or physical procedures.
- Renal failure patients requiring hemodialysis should
not be tested during dialysis therapy.
Interpreting the REE
Interpreting the measured REE includes comparing the results to the
predicted level of energy needs for that individual. Determining the 24
hour calorie intake of that individual from either an oral diet or
specialized nutrition therapies (through feeding tubes into the
gastrointestinal tract or intravenous administration) is required.
It is important to assess the RQ to make certain it is within
physiological range and consistent with the person's calorie intake
and medical history. The physiological range of RQ is 0.67 to 1.3. This value
represents the combination of carbohydrate, fat and protein being used
for energy. If the RQ is greater than 1.0, decrease the total calorie
intake and adjust the carbohydrate to fat ratio. If the RQ is less
than .81 increase the total calorie intake, dependent on the goal for
the nutrition therapy. Food sources and conditions have specific RQ
values that are useful when interpreting the REE and making
recommendations for changing dietary goals and feeding regimens. (1,4,5)
Energy source/condition RQ
prolonged ketosis <0.70
mixed energy 0.85
fat storage >1.00
Use of REE in conjunction with weight management programs
In weight management programs, when an individual has trouble losing
weight a frequent comment is that ones metabolism is slow. This can
result in failure of the individual to adhere to a weight management
program incorporating a reduction in total daily calorie intake.
However, once the actual REE is done, there is no longer need
to speculate about the normalcy of metabolism for that person.
Successful maintainers of weight loss report continued consumption of a
low-energy and low-fat diet. (8) Efforts to improve weight loss and
maintenance need to focus on strategies to increase calorie expenditure
through exercise and an appropriate diet based on measured energy needs.
The goal is a lifelong commitment to healthful lifestyle behaviors. (6)
An example of how to successfully use the REE measurement in a weight
management program requires interpretation and counseling by a
registered dietitian. After measuring the REE and calculating the 24
hour intake, the individual would be instructed on reducing their food
consumption by approximately 200-300 calories a day below the
measured REE. This should result in about 1 pound weight loss per week
with additional weight loss due to exercise. If the REE is extremely
low then the focus would be on maintaining the calorie intake at the REE
level and gradually increasing to at least 30 minutes of enjoyable
activity each day.
Clinicians monitoring weight management programs would be able
to determine if their clients are actually following a reduced calorie
diet based on REE, RQ and the amount of weight loss. These
measurements would be very useful in detecting failure to adhere
to the diet and facilitate better understanding by the client in
achieving his/her weight goal.
It is important that an individual have a framework for making healthful
food choices to obtain realistic weight reduction and maintenance
goals. The challenge is to balance adequate nutrient intake with the
individual's desire to lose weight rapidly and to address the numerous
myths concerning diet modification. The REE takes the guesswork out of
determining the goal for the calorie intake to achieve the desired
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