1. Current Evidence for Estimating Energy Requirements
Clare Soulsby, Research Dietitian

2. Main components of energy expenditure:
basal metabolic rate (BMR)
alteration in BMR due to disease process (stress factors)
activity
diet induced thermogenesis (DIT)

3. Estimating BMR: controversies
basal metabolic rate (BMR) vs. resting energy expenditure (REE)
prediction equations vs. measured energy expenditure (MEE)

4. Conditions essential for measuring BMR
post-absorptive (12 hour fast)
lying still at physical and mental rest
thermo-neutral environment (27 – 29oC)
no tea/coffee/nicotine in previous 12 hours
no heavy physical activity previous day
gases must be calibrated
establish steady-state (~ 30 minutes)
* if any of the above conditions are not met = REE

5. Estimating BMR: controversies
basal metabolic rate (BMR) vs. resting energy expenditure (REE)
prediction equations vs. measured energy expenditure (MEE)

6. Estimating BMR: prediction equations
may over or under-estimate (compared with MEE)
inadequately validated
poor predictive value for individuals
open to misinterpretation
(Cortes & Nelson, 1989; Malone, 2002; Reeves & Capra, 2003)

8. Estimating BMR:which equation?
Harris-Benedict
Schofield Equations
disease specific eg Ireton Jones
Kcal/kg

9. Estimating BMR: Harris Benedict Equations
Developed in 1919
From data collected between 1909 and 1917 (Harris Benedict 1919)
Study population:
136 men; mean age 27 ± 9 yrs, mean BMI 21.4 ± 2.8
103 women; mean age 31 ± 14 yrs, mean BMI 21.5 ± 4.1
Tends to overestimate in healthy individuals (Daly 1985, Owen 1986, Owen 1987)

10. Estimating BMR: Schofield Equations
developed in 1985 (Schofield 1985)
meta analysis of 100 studies of 3500men and 1200 women
studies conducted between 1914 and 1980 (including Harris Benedict data)
2200 (46%) subjects were military Italian adults
88 (1.2%) subjects were >60 years
SE kcal/d (women) kcal/d (men) (Schofield 1985)

11. Estimating BMR: disease specific equations
developed for specific patient groups (Ireton Jones 1992, Ireton Jones 2002)
advantage over Schofield/ HB equations:
Schofield /HB estimate BMR of a healthy individual then necessary to adjust for disease using a stress factors
disease specific equations include patients in their database so aim to more accurately reflect BMR of hospitalised patients

12. Estimating BMR: Ireton-Jones energy equations
ventilated and breathing ICU patients
3 x 1 minute measurements 200 patients
unclear whether measurements took place during feed infusion/ after treatment etc
52% burns, 31% trauma
validation studies, IJEE had a better agreement with MEE:
HBx1.2, HBx1.3, 21kcal/kg

13. Estimating BMR Schofield equation derived using meta analysis:
greater power than small/ local studies
compiled from unstructured data set obtained for diverse reasons:
problems with sampling assumptions
accuracy approx ±15%
disease specific equations useful in some circumstances

14. Estimating BMR
what about:
the elderly?
the obese?

15. Estimating BMR: the elderly
Original Schofield equations:
only 88 (1.2%) of subjects >60 years
particularly unsuitable for >75yr
included data on subjects from the tropics
Revised equations for the elderly:
published in the 1991 COMA (DH 1991)
include additional data from 2 studies; 101 Glaswegian men (60-70yr) 170 Italian men and 180 Italian women
excluded data collected in the tropics

16. Estimating BMR: Obesity
equations (such as Schofield) are linear
weight increases linearly with estimated BMR
may overestimate in obese

17. Estimating BMR: obesity
BMI
% of Schofield database
% of UK population (DOH 1999)
> 25
14.6%
40.8%
> 30
4.5%
9.7%

18. Estimating BMR: Obesity
obese data primarily obtained from 2 groups:
Burmese hill dwellers
retired Italian military
there were significant differences in weight/ BMR association between groups, Italian group showed greatest difference
obese subjects in Schofield data may not be a statistically representative sample of the population is general

19. Estimating BMR: Obesity
recent (Horgan 2003) reassessed validity of the Schofield data to predict BMR in obese
conclusions:
BMR increases more slowly at heavier weights
to ignore this is to over predict energy requirements
any general equation for predicting BMR may be biased for some groups or populations.

20. Estimating BMR: adjusted body weight (ADJ)
estimate of how much of the extra body weight is lean and thus metabolically active
2 methods:
25% adjusted weight
= (actual body weight x 0.25) + ideal body weight
adjusted average weight
= (actual body weight + ideal body weight) x 0.5

21. Estimating BMR: adjusted body weight (ADJ)
first reported in newsletter Q&A format
not validated
studies suggest adjusted average weight has better predictive value than 25% adjusted weight (Glynn 1998, Barak 2002)
no longer included in ASPEN guidelines (2002)

22. Estimating BMR: Obesity
predicting BMR is very difficult (without measuring lean body mass)
adequacy of specific equations? (Ireton-Jones et al., 1992; Glynn et al., 1998)
actual body weight + stress + activity = overestimate
access to indirect calorimetry is limited

23. Determining energy requirements in obesity
non stressed patients:
calculate as normal and kcal for decrease in energy stores
mild to moderately stress:
calculate as normal
omission of stress and activity avoids the adverse effects of overfeeding
severe stress
might be necessary to add a stress factor to BMR
*monitoring essential eg blood glucose

24. Estimating energy requirements
The main components of energy expenditure are estimated:
BMR
Alteration in BMR due to disease process (stress factors)
Activity
DIT

25. Levels of evidence 1. a) Meta-analyses
b) Systematic reviews of randomised controlled trials (RCTs)
c) RCTs
2. a) Systematic reviews of case-control or cohort studies
b) Case-control or cohort studies
3. Non-analytic studies e.g. case studies
4. Expert opinion
(adapted from: Draft NICE Guidelines for Nutrition Support in Adults, 2005)

26. Stress factors timing of measurements
over (hyperalimentation) vs. under-feeding
changes in therapeutic interventions
e.g. improved wound care, anti-pyretics, sedation, control of ambient room temperature
 err towards lower end of the range and monitor

27. Stress factors
unable to include a stress factor for every disease or condition
many measured in far from ideal circumstances
limited by data available
may choose to underfeed in certain circumstances
necessary to refer back to the literature
included a checklist of factors to look for when reviewing papers

28. Adverse effect of over-feeding
excess carbohydrate:
difficulties controlling blood glucose
increased CO2 production
respiratory problems in vulnerable patients (eg COPD/ ventilated)
swings in blood glucose increase mortality in critically ill
aim not to exceed the glucose oxidation rate (4-7 mg glucose/ kg/ min)
long term excess carbohydrate can lead to steatohepatosis or fatty liver (Elwyn DH, 1987).

29. Estimating energy requirements
The main components of energy expenditure are estimated:
BMR
Alteration in BMR due to disease process
Activity
DIT

30. Total energy expenditure
Activity
+ DIT
Activity
+ DIT
BMR
BMR
Health
Disease

31. Activity factor
energy expended during active movement of skeletal muscle
approximately 20-40% of energy expenditure in free living individuals
depends on duration and intensity of the exercise
activity is less than 20% of the energy expenditure in hospitalised or institutionalised
NB assumes normal muscle function

32. Activity factor for activity: institutionalised patients combined with DIT
Activity level
Males and females
Bedbound immobile
Bedbound mobile/ sitting
Mobile on ward
+ 10%
+ 15 – 20%
+ 25%

33. Activity factor:abnormal muscle function
hospital patients likely to have higher activity levels:
abnormal neuro-muscular function e.g. brain injury, Parkinson’s, cerebral palsy, motor neurone disease, and Huntington’s chorea
prolonged active physiotherapy
effort involved in moving injured or painful limbs

34. Community patients
free living individuals have higher energy expenditure due to physical activity
nursing home and house bound patients ? similar activity levels to hospital patients
for active patients in the community a PAL should be added

35. Physical activity level (PAL) of adults
Non-occupational activity
occupational activity
light
M F
moderate
mod/ heavy
M F
non active
m. active
very active

36. Estimating energy requirements
The main components of energy expenditure are estimated:
BMR
Alteration in BMR due to disease process
Activity
DIT

37. Diet-induced thermogenesis
Continuous infusion of enteral feed and parenteral nutrition do not significantly increase REE
Bolus feeding increases REE by ~ 5%
Mixed meal increases REE ~ 10 %
PALs include DIT (COMA, 1991)
 guidelines include combined factor for activity and DIT

38. Estimating requirements: sources of error
prediction equation for BMR
stress factor:
degree of stress inaccurately assessed
poor evidence to support stress factor used
activity level inaccurately assessed or poorly understood
DIT varies by 10% depending on feeding method

39. Sources of error: inaccurate weight
Inaccurately measured weight
estimated weight
inaccurate scales
patient had their feet on the floor (chair scales)
patient was fluid overloaded ( 20% of hospital patients)
amputees

41. Conclusions Estimated requirements are only a starting point
- set realistic goals of treatment for each patient
- monitor and amend as patient’s condition changes
Review and criticise the literature regularly
- be aware of gaps in the evidence
- understand the limitations of guidelines
- check applicability to your patients
Contribute to research and audit projects