Resting Energy Expenditure "REE"
By Denise Schwartz, MS, RD, FADA, CNSD
What does REE mean?
Resting energy expenditure (REE) 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 persons. (2)
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 ? VCO2)? 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: (1,4,5)
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 depressants.
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 minute test.
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 outcome.
1. Feurer I and Mullen JL. Beside measurement of resting energy expenditure and respiratory quotient via indirect calorimetry. NutrClin Prac. February 1986;1:43-49.
2. Frankenfield DC, et al. The Harris-Benedict studies of human basal metabolism: history and limitations. J Am Diet Assoc. 1998;98:439-445.
3. Garrel DR, et al. Should we still use the Harris and Benedict equations? Nutr Clin Prac. June 1996;11:99-103.
4. Matarese L. Indirect calorimetry: technical aspect. J Am Diet Assoc. 1997;97(suppl 2):S154-S160.
5. McClave SA and Snider HL. Use of indirect calorimetry in clinical nutrition. Nutr Clin Prac. October 1992;7:207-221.
6. Position of The American Dietetic Association: weight management. J Am Diet Assoc. 1997:97:71-74.
7. Schwartz DB: Pulmonary failure. IN Matarese LE and Gottschlich MM:
Contemporary Nutrition Support Practice. Philadelphia, W. B. Saunders, Co. (In press)
8. Shick SM, et al. Persons successful at long-term weight loss and maintenance continue to consume a low-energy, low-fat diet. J Am Diet Assoc. 1998;98:408-413.
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