Energy Considerations in Nutrition

00:01 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.

00:12 These things include basal metabolic rate as well as body mass index, total energy expenditure, as well the fuel caloric values and so forth.

00:23 So moving into - looking at basal metabolic rate, most often we'll consider resting metabolic rate.

00:30 Because it's the much more simple measurement to make.

00:33 Resting metabolic rate doesn't take into account having to have 12 hours of fasting and necessitate 8 hours of sleep.

00:42 It's a simple measurement taken upon waking and getting up.

00:47 So resting metabolic rate is generally, we use in an equation to calculate our basal metabolic rate.

00:57 But if we are going to do it very clinically, we would measure the VO2 at various times, on various days.

01:05 But again we will generally use an equation to calculate basal metabolic rate.

01:11 And I'll introduce you to or help you review two of them that will be important for you to keep in mind.

01:18 This first one, you probably just need to know the name of.

01:23 But if you want to go beyond that, you could memorize the equation.

01:27 We're not going to spend the time deriving it.

01:30 But it takes into account the age of the individual as well as the gender weight and height.

01:36 And you can see that there is an adjustment over there on the right hand side based on the gender.

01:43 Whether it's a male or a female.

01:45 And again you don't need to understand where the numbers come from.

01:50 It's a plug and chug kind of thing, Measuring height in centimeters and weight in kilograms.

01:55 More commonly, these days though the Katch-McArdle formula is utilized in which we consider pretty standard numbers.

02:06 Let us say a woman has 25% body fat, if she weighs 50 kgs, her lean mass would be 50x0.75 = 37.5 kg. BMR can then be computed to be equal to BMR = 370 + (21.6 x lean mass).

02:25 The catch here is that we have to know the body fat percentage.

02:30 And that turns out to be not so difficult to ascertain these days.

02:35 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.

02:47 So we can calculate lean mass by subtracting the body fat percentage.

02:54 So Katch-McArdle is the one I would certainly commit to memory and keep in your pocket for use on your exam.

03:01 Now total energy expenditure is the energy we use beyond our basal metabolic requirements.

03:11 Plus, all the other things that we do in a day.

03:14 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.

03:26 That when we consume food it actually costs as calories to consume and digest that food.

03:35 So that is the thermic effect of feeding.

03:38 And that's about a 10% of our total energy expenditure in a day.

03:43 Now of course in addition to that we have some physical activity.

03:47 Some of that physical activity is activity that we choose to do as we move around.

03:52 But even when we are sitting still, we are still burning calories.

03:58 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.

04:11 So there's the component of physical activity that we call NEAT.

04:18 Another term you should be familiar with.

04:19 Which is our Non-Exercise Activity Thermogenesis.

04:22 So this is when your sitting at your desk and you feel like you're doing nothing and not burning any calories.

04:28 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.

04:36 So all of these pieces go into the calculation of total energy expenditure.

04:43 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.

05:00 But in general we will take our basal metabolic rate and multiply it by a certain factor dependent on the activity level.

05:11 So someone who is sedentary will have a lower factor to multiply by than someone who is particularly active.

05:16 Again you'll see a vast difference in the actual figures provided.

05:24 What I recommend is that you get a perspective of what sort of factor it is.

05:29 So somewhere between 1 and 2.

05:33 However, we really know that there are extreme athletes.

05:36 People that are riding century rides.

05:38 Ultramarathoners might run 50 miles in a day.

05:42 They are certainly going to be above the extremely active level.

05:47 So you might even see numbers towards 3. So don't go memorizing the numbers.

05:51 Just sort of get a relative idea that physical activity is multiplying the basal metabolic rate by a particular factor.