Energy Considerations in Nutrition: BMR, RMR & Physical Activity – Nutrition | Lecturio

In this lecture
we will be reviewing some of the energy considerations relative to nutrition that you need to have right
in your pocket for your medical licensing
exams. These things include basal
metabolic rate as well as body mass index, total energy expenditure, as well the fuel caloric
values and so forth. So moving into – looking
at basal metabolic rate, most often we’ll consider
resting metabolic rate. Because it’s the much more
simple measurement to make. Resting metabolic rate doesn’t
take into account having to have 12 hours of fasting and necessitate 8 hours
of sleep. It’s a simple measurement taken
upon waking and getting up. So resting metabolic
rate is generally, we use in an equation
to calculate our basal metabolic rate. But if we are going to
do it very clinically, we would measure the VO2 at
various times, on various days. But again we will generally
use an equation to calculate basal metabolic rate. And I’ll introduce you to
or help you review two of them that will be important for you
to keep in mind. This first one, you probably
just need to know the name of. But if you want to go
beyond that, you could memorize the equation. We’re not going to spend
the time deriving it. But it takes into account
the age of the individual as well as the gender weight
and height. And you can see that there
is an adjustment over there on the right hand side
based on the gender. Whether it’s a male or a female. And again you don’t need to
understand where the numbers come from. It’s a plug and
chug kind of thing, Measuring height in centimeters
and weight in kilograms. More commonly, these days though
the Katch-McArdle formula is utilized in which we consider
pretty standard numbers. Basal metabolic rate equals 370 + 21.6 times
the lean mass in kilograms. The catch here is that we have
to know the body fat percentage. And that turns out to be
not so difficult to ascertain these days. Of course you can do
Caliper testing but there are bioelectrical impedance devices that patients can just hold
on to and we get a fairly decent estimate or at least relative estimate
of the body fat percentage. So we can calculate lean mass by subtracting the body fat percentage. So Katch-McArdle is the one
I would certainly commit to memory and keep in your pocket for use on your exam. Now total energy expenditure
is the energy we use beyond our basal metabolic requirements. Plus, all the other things
that we do in a day. So all our caloric needs
over a 24 hour period, first of all you probably
realize but maybe haven’t thought about it in the total
energy expenditure realm. That when we consume food it
actually costs as calories to consume
and digest that food. So that is the thermic
effect of feeding. And that’s about a 10% of
our total energy expenditure in a day. Now of course in addition to that we have some physical activity. Some of that physical activity
is activity that we choose to do as we move around. But even when we are sitting still, we are still burning calories. And we need to add
this physical activity, whether it’s intended
exercise or general mobility, we need to add this to
our basal metabolic rate. So there’s the component
of physical activity that we call NEAT. Another term you should
be familiar with. Which is our Non-Exercise
Activity Thermogenesis. So this is when your sitting
at your desk and you feel like you’re doing nothing
and not burning any calories. In fact, we are burning calories
during that because we have to have muscles firing
to keep us upright and not in a pile on the floor. So all of these pieces go
into the calculation of total energy expenditure. And then how do we
calculate the physical activity piece
of this. This is can be pretty
controversial calculation I suppose because as always
when people give us numbers, they vary from source to source. But in general we will take
our basal metabolic rate and multiply it
by a certain factor dependent on the activity level. So someone who is sedentary will
have a lower factor to multiply by than someone who is particularly active. Again you’ll see a vast
difference in the actual figures provided. What I recommend is that you get
a perspective of what sort of factor it is. So somewhere between 1 and 2. However, we really know that
there are extreme athletes. People that are riding
century rides. Ultrmarathoners might run
50 miles in a day. They are certainly going
to be above the extremely active
level. So you might even see numbers
towards 3. So don’t go memorizing
the numbers. Just sort of get a relative idea that physical activity is multiplying the basal metabolic rate by a particular factor.

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