This content emphasizes the importance of accurately measuring energy expenditure, particularly Resting Metabolic Rate (RMR), using indirect calorimetry instead of relying solely on predictive equations, to optimize nutrition and weight management strategies for individuals.
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hello everyone this is carol ironton
jones i'm a registered dietitian and
consultant in private practice
i'm happy to bring you this webinar
today indirect calorimetry and energy
expenditure should we guess or should we
measure the objectives are as follows to
evaluate components of energy
expenditure in adults
to understand the measurement of energy
expenditure using indirect calorimetry
and to discuss the application of energy
expenditure assessment across the
energy expenditure is the sum total of
voluntary and involuntary energy
expenditure in a day
energy is expended in the human body for
micro processes such as active transport
synthesis of macromolecules and muscle contractions
contractions
what affects energy expenditure age
age
younger versus older gender male versus
female body surface area or height and weight
weight
activity size stature race and other
things including climate and smoking
some of these have a large effect and
some have a smaller effect on overall
energy expenditure
components of total energy expenditure
or te or sometimes called daily any
energy expenditure include
basal metabolic rate which is about 60
to 80 percent of total energy expenditure
expenditure
resting metabolic rate which is
approximately 10
above basal metabolic rate and really
represents 60 to 75 percent of total
energy expenditure in free living people
then it added to that is the thermic
effect of food which is an increase of
about six to ten percent
above uh the resting metabolic rate
then the last two activity and and or
first let's discuss basal energy
expenditure or basal metabolic rate it
is the minimum amount of energy expended
that is compatible with life
it reflects the amount of energy used
over 24 hours while physically and
mentally at risk at rest in a
thermo-neutral environment
that prevents the heat generating
activities of exercise and other
processes even shivering
you can imagine that this would be very
difficult to measure if i was going to
measure this in one of my patients i'd
have to have a key to their house and go
to their home and
right as they were waking up just wake
them up in a hopefully they were in a
thermo-neutral environment
and had no stresses nothing on their
mind and i would measure their basal
metabolic rate but that's not very easy
to do and not really something that we
use in clinical practice
so what we
measure in clinical practice is resting
metabolic rate
you may see that as ree as well as you
can see from this slide this is the
energy expended in the activities
necessary to sustain normal body
functions and homeostasis
it includes these
items here respiration and circulation
synthesis of organic compounds energy
required by the central nervous system
each of these are involuntary energy expenditure
expenditure
in fact sixty percent of resting
metabolic rate can be accounted for by
the heat produced by the liver
brain heart and kidneys and so that's
heat produced or we can call that energy
expenditure as well
so rmr or ree is what we can measure it
is about 10 percent above bmr and it
accounts for somebody being awake and
potentially traveling to the site to
have their energy expenditure measured
the next component of energy expenditure
is the thermic effect of food this is
called tef it could be called diet
induced thermogenesis it could be called
specific dynamic action so
any one of these are
a definition of the increase in energy
expenditure associated with the consumption
consumption
digestion and absorption of food and
this accounts for up to 10
of the total energy expenditure it can
be as low as six percent and as or as
high as 10 percent
the thermic effect of food is increased
more with a high protein meal compared
to a high fat meal but remember it's
still within this ten percent increase
above resting metabolic rate
fat is metabolized efficiently with only
four percent wastage compared to about
25 wastage when carbohydrate is converted
converted
to fat for storage
the thermic effect of food decreases
after ingestion of food over two to four
hours and this depends on the size of
the meal so a
a
lower calorie meal of around 300
calories the thermic effect this
increase above resting metabolic rate
may be complete after two to three hours
a higher
energy containing meal may be four hours
spicy foods do enhance and prolong the
effect of the thermic effect of food
so meals with chili and mustard may
increase the metabolic rate as much as
33 percent more than unspiced meals and
this effect maybe may last for more than
three hours but this important point is
that this is a short-lived and in
reality this is a small number of calories
calories
if your rmr was 1200 calories then for
three hours at 33 percent increase will
give you a total of additional 50
other factors also affect
energy expenditure
endocrine disorders i e
hyperthyroidism or hypothyroidism
may affect energy expenditure if untreated
untreated
emotional excitement or stress can
increase energy expenditure
there's an increase in energy
expenditure in pregnancy
this is
smaller at the first trimester
increasing over each trimester
butte and colleagues in houston
estimated for the first trimester
there's about a 90 calorie per day
increase in energy expenditure for the second
second
trimester about a 300 calorie per day
increase in energy expenditure and for
the third trimester around 450
calories uh increase in energy
expenditure per day so that
can average out to
around 450 calories
per day again more at the
second and third trimester all of this
is a goal to gain about 24 pounds
there's also an increase in energy
expenditure for lactation and this has
been estimated to require four to 500
extra calories per day or an increase in
energy expenditure of about 400 to 500
calories per day
for post menopausal females there is
actually a decrease in rmr due to the
loss of post
ovulation increase in resting metabolic
rate so postmenopausal females may have
a decrease in their resting metabolic
rate of fifteen thousand to twenty
thousand calories per year that first
year however that is only around forty
one to fifty five calories
other factors
other factors that it may increase
energy expenditure inc include caffeine
nicotine alcohol and fevers but it is
important to note with any of these that
these are short-lived for example
caffeine may increase your energy expenditure
expenditure
up to
as you see here 11 percent or 15 percent
but on average it's around 6 percent
and it depends on the amount of caffeine
taken in and the six percent increase
may last for four hours
nicotine also increases resting
metabolic rate
and this increases that
less for approximately 2.5 hours
fevers do increase resting metabolic
rate and from this old data from 1930
it was estimated that resting metabolic
rate is increased by seven percent for
each degree of increase in body
temperature above normal
but again
this is should be short-lived because
this should be treated a high
temperature is not something that is
activity or the energy expended in
activity is very difficult to estimate
it's the most variable
component of total energy expenditure
and for some people who do very little
in a day they may increase their energy
expenditure only approximately 100 calories
calories
an elite athlete may increase their
energy expenditure by 3 000 calories or
more per day per day
so this is quite a challenge in
estimating energy needs for individuals
looking at this schematic you can see
that we've talked about many of the
things that are associated with energy expenditure
expenditure
and really
physical activity turns out to be the
biggest challenge and biggest variable
but if this is a normal individual
if you gain weight then you either need
to increase your cap decrease your
calories or increase your physical
activity if you're losing weight
then you need to increase your energy expenditure
expenditure
the challenge comes when this is
replaced by disease or injury
so if you do have a disease or injury
we must account for the increase or
potentially decrease in energy
expenditure because of this injury or disease
disease
it again becomes difficult to estimate
the number of calories that
that
are associated with any diagnosis as you
see here in this slide
in cancer if this is an old slide but this
this
continues to hold true today
energy expenditure cannot be accurately
estimated in patients with cancer
metabolic rate varies
similarly with liver disease copd and
even pressure ulcers
so what do we do
we try to predict how many calories our
patients need we use energy expenditure equations
equations
energy expenditure equation factors
usually include height they include body
weight they include age and gender
noting here height should be
measured but often time it is estimated
body weight
should be measured as well
some people use an ideal body weight but
as you can see here if i'm 5'4 and a female
female
my ideal body weight is
pounds whether i am old or young fit or
not fit so body weight also needs to be measured
measured
if it cannot be measured then it
causes the energy expenditure equation
to be inaccurate
components of body weight that would be
nice to be measured are fat mass and fat
free mass but often this is not available
available
and may not be included in an energy
expenditure equation
finally age and gender should be
accounted for
the effect of resting metabolic rate on
on
energy expenditure is usually due to the
effect of both age and gender
in the variation in fat mass and fat
free mass and therefore weight
adjusted body weight has been used for
estimating the
body weight to be used in an energy
expenditure equation
for an overweight or obese individual as
you see here the data behind this is a
newsletter that was published in 1984.
this equation has been used but it has
no data behind it and so you should do
as this dietitian is doing to her
patient and that is she is measuring her
actual body weight to use in the energy
there is an equation that is used primarily
primarily
in the outpatient setting i use it in my
practice it can be used for healthy
individuals it's the mifflin store equation
equation
it was considered new but as you can see it's
it's
from 1990 so it's actually almost a 30
year old equation however it has a large
number of patient individuals healthy individuals
individuals
in the equation almost 500 and there
were several who had a bmi greater than 30.
30.
this is the mifflin saint jor equation
it uses weight actual weight height and
age to estimate
resting metabolic rate
in healthy individuals
energy expenditure equations and
critical care
have many factors that may influence
resting metabolic rate height weight age
gender may also
may affect resting metabolic rate we
know that
also minute ventilation if the patient
is ventilator dependent body temperature
again whether they're ventilator
dependent or spontaneously breathing the
type of nutrition support they're
receiving if they're septic
so these are just some of the many
factors that influence resting metabolic rate
rate
so applying a prediction equation
developed for normal healthy subjects to
critically ill patients
will likely result in significant errors
this equation
i developed in 1992 it's still used for assessing
assessing
or estimating energy expenditure in
hospitalized patients there are two
equations one for ventilator dependent
patients one for spontaneously breathing patients
patients
in the evidence analysis library of the
academy of nutrition and dietetics the
1992 version was recommended to be used
and it is here with the reference listed
here as well because
because
this is was developed from
indirect calorimetry
of individuals
who were in the presence of their
disease or injury
it estimates their actual total energy
expenditure so no additional factor is
another equation that is used for
hospitalized patients is the penn state
equation as you see here
for obese patients who
are a bit of a conundrum
there are three equations that have been recommended
recommended
some recommend using 25 calories per
kilogram using actual
or usual current body weight
some recommendations are 15 to 20
calories per kilogram using
using
actual body weight
it has been recommended to use the
ariton jones equation or the penn state
equation and then finally it
it
has been
this equation has been used the
hypocaloric high protein feeding where
you pre determine the patient's resting
metabolic rate and you give them about
50 percent of those calories which again
that turns out to be this 14 to 20
calories per kilo but you do give them
adequate protein using their ideal body
well as you can see there's many
problems with those equations so how can
we determine actual energy expenditure
energy expenditure can be measured from
respiratory gas exchange
oxygen is consumed in every energy
producing reaction co2 is produced and
this occurs in the krebs cycle
so if we can determine the actual oxygen consumption
consumption
and co2 production then we will know the
number of calories this patient requires
or help the individual for that matter
the weir equation is used to plug in
these measured numbers oxygen
consumption and co2 production
also if you know the amount of oxygen
consumed and co-produced co2 produced
then you will be able to understand
what metabolic substrates are being utilized
utilized
by calculating respiratory quotient
which i'll show you in a moment
this is the weir equation
the abbreviated weir equation is used
most often now as urinary nitrogen is rarely
rarely available
available
and fraught with inaccuracy so this is
the equation that is used
most metabolic cards or indirect
calorimeters have this equation already
programmed in so there's no need for you
to memorize it but it's a good one to
know so you know what your
metabolic cart is calculating from
some indirect calorimeters measure
oxygen consumption only and they use an
respiratory quotient rq is the ratio of
oxygen consumed to co2 produced so
that's vco2 over
vo2 so for fat the rq is 0.7
and all the way up to carbohydrate is
0.95 to 1. but
for a mixed diet which most people have
the rq is about 0.85
if the rq is above one that may indicate
over feeding or net fat synthesis and if
the rq is significantly over one as you
see here 1.1
that likely indicates hyperventilation
and you will not have an accurate test
if the rq is below
so how are metabolic
how are these indirect calorimetry
measurements made they are made using
what we call an indirect calorimeter or
a metabolic measurement cart
there are larger versions they measure
oxygen consumption co2 production
respiratory quotient and of course
resting metabolic rate
they may
measure pulmonary function as well many
are connected to a ventilator or as a
component of a ventilator
they're expensive and they require
experienced personnel to operate and
calibrate these as well and they're
usually not very portable
there are portable indirect
calorimetries they measure
indirect calorimeters measuring oxygen
consumption and determining resting
metabolic rate these small ones as you
see pictured here which is the review is
they are like this one is portable
lightweight and self-calibrating
and it's been
clinically validated against douglas bag
and existing metabolic carts
it is used with spontaneously breathing
patients only and as you can see here
she's got nose nose clips and a
mouthpiece to have her metabolic rate measured
measured
here's another example of what somebody
would look like having their metabolic
rate measured using the review and as
you can see they're in a supine position
and i'll show you the
measurement conditions in a moment
is there evidence to support using
indirect calorimetry instead of
equations to estimate calorie
requirements that is can resting
metabolic rate be measured reliable the
answer is yes under standard conditions
to obtain a steady state rmr
how often should they be measured
for healthy individuals you can measure
them once in a 24 hour period
it's true as well for critically ill
ventilated patients you can measure them
once in a 24 hour period if a steady
state is achieved
how long is the measurement
one single 10 minute measurement
should be adequate as long as you
eliminate the first five minutes
and the vo2 and vco2 are within a 10 variation
variation
if you'd like more information on this i
would like to refer you to the article
by fulmer and colleagues in the journal
of the academy of nutrition and
measurement conditions this is very
important to ensure you have an accurate
measurement before the resting metabolic
rate measurement for adults
food should be limited
or should be actually eliminated a fast
for seven hours
or four hours if a small meal has been
taken in
i measure most of my patients between 8
and 11 a.m so that gives them time to
have fasted overnight
most everyone has
caffeine none for four hours nicotine
none for 2.5 hours and exercise none for
four hours although there's not good
data to show how long someone should
refrain from exercise
i use this rule of force no food
caffeine nicotine or exercise for four
hours before the rmr measurement and
i've found this to be very acceptable to
my clients and also provides
measurement conditions the the
individuals that you measure have had to
travel to your site
so i have my uh clients come in and they
rest before them rmr for about 20 to 30
minutes so yes they come into my office they
they
lie in a supine position
i turn off the light i have a lamp on my
desk and they rest for 20 minutes i time it
it
as far as gas collection devices any gas
collection device is fine the ventilated
hood and canopy is fine mouthpiece and
nose clip is fine and a face mask is fine
fine
i like the mouthpiece and nose clip
recently i had a man come in with a very nice
nice
beard and
mustache and that would have been very
difficult to measure with a face mask
the ambient room temperature should be
somewhere between 72 to 77 degrees that
is in a comfortable environment and you
should have
it quiet and there should be dim light
once the rest period is over you can
start the test and
i use the review so my tests are usually
then they get the results
how many calories do i need well as you
see here energy in to equal energy out
should mean
that you're in energy balance so
so
typically you do add an activity factor
for the rmr and this is the challenge
the rmr
measurement is very exact and then we
add an estimated activity factor
i use 30 percent for almost all of the
clients that i see
if you have somebody who is very active
they have an active child
active job they're a regular exerciser
they're a weekend warrior then you may
add 50 percent to their resting
metabolic rate to get their total energy expenditure
expenditure for
for calories
calories to
to
cause weight gain you can add 250 to 500
calories per day or subtract the same
amount but again this is why they need
to be monitored to make sure you're
let's go through some case reports
this is a 60 year old female
and i thought carmen diaz looks great
for a 60 year old female
this female is 6 1 61 inches 126 pounds she's
she's
been on
weight loss diets most of her life she's
about 23 percent body fat so her
predicted resting metabolic rate would
be 1207 calories but actually her
measured resting metabolic rate was
936 calories per day
what are your recommendations well my
recommendations to her
were one to increase her activity but
also to increase her
energy intake still she wanted to
decrease her body weight but i
recommended that she take in at least 12
or 1300 calories per day
and my goal is to measure her again and
see if by consistently increasing her intake
intake
and potentially building lean body mass
we can move her resting metabolic rate up
yes
george clooney came to my office the
other day he's a 62 year old male
this particular guy was 68 inches tall
he weighed 191 pounds he had a bmi of 29.1
29.1
he started a strength training program
and a weight loss program his predicted
resting metabolic rate was 1500 calories
approximately but his measured
was 1700 calories
six weeks later
later
he has lost uh
down to 183 pounds so he's lost eight
pounds but he has gained muscle mass his
bmi is 27.5
and his predicted resting metabolic rate
with the
calorie change here was 1541 calories
per day but his measured was actually
1634. so although his metabolic rate has
decreased he has come more within what
we would predict the normal range
as noted by the mifflin saint jorah equation
equation
and finally a couple more this is that
39 year old male 70 inches tall weighed
200 pounds his predicted was 1940 kcals
per day but is measured was
was
1613 calories per day another one 44
year old female 69 inches tall 169
pounds bmi 25
right in that range of
normal to overweight bmi
her predicted was 1506 and her measured
was 1512 calories per day
so as you can see each one of these four individuals
