This week, we're going to discuss the macronutrient protein.
When we think about proteins, we can construe those to be the building blocks
of human anatomy. They serve many functions and are crucial
for growth, development, and maintenance of the human being.
When we think about this analogy that we are what we eat, proteins that we eat,
like lipids, become proteins in our body. I've also made an analogy to the idea
that human beings, the body is somewhat like a factory.
We can think about this human factory producing various products and needing
other products to run, to run efficiently and to manufacture what it needs to
manufacture. When you think about calories, proteins
do have calories, calories are fuel. Now remember, carbohydrates are the
preferred fuel source for our bodies. They are what stoke the fire of the
factory. Lipids help run the show.
They make sure everything is running properly, keep things lubricated.
They make sure that products are delivered to the right locations.
They help us synthesize hormones that we need to regulate This mechanism its
factoring. Proteins not only build the factory, but
they're also very important for the running, and the regulating of the human
body. So, we consider these proteins as the
building blocks of the human body, we really need to discuss amino acids.
So truly, if the amino acids that are the blocks of all proteins creating proteins
whether they are, you know, plants, animal or in our own body and tissues.
Let's take a look at amino acids. Amino acids have similar chemical
construct, one difference is the side group.
This is what will really identify a protein, it's what makes a protein one
amino acid. Different from another.
They all have this central carbon. The amino and acid group has amino acid
and a hydrogen. Various amino acids are either essential
or non-essential, depending on that side group.
There are amino acids such as aspartate. So compare that to, for example, alanine.
Phenyalanine, so you can see that these are groups, this side group can be simple
or complex. Here we see one with a ring structure to
it. To it.
Glycine, very simple, just a hydrogen, so you can read in your text book what
specifically which amino acids specifically are essential versus others,
but to just give a better understanding of what this means simply is we can not
synthesise, The non-essential amino acids.
Something about their chemical structure that are a group while we are not
synthesizing that amino acid. Non-essential amino acids can be
synthesized. Now, we do need essential-amino acids in
order to do so but we can actually manufacture certain amino acids in the
body. In this process, we actually break down
the components of another amino acid to make a new amino acid.
So if we take amino acid A off at the top left,
we convert that to amino acid B, down at the bottom right.
We're simultaneously converting a-keto acid, keto acid b to keto acid a.
So look at the chemical structure of a, look at the difference in amino versus
the keto. What's changed? We see that NH2 group.
That amino group is what's changing from a keto acid to amino acid.
Makes sense. So amino acids make protein.
Proteins are one of those complex macro-nutrients structurally.
We have a specific sequence of amino acids that will come together, then fold
in another specific sequence, and then different proteins can actually.
Work together to create a complex protein.
Example of this is haemoglobin. Now, haemoglobin is a complex structure
made of four sub units of protein and you can look that up in your text book as
well, little bit about protein structure. So I'd like you to understand at this
level, is that when we look at a protein whether it be in a food or in a body, the
breakdown of that protein or the denaturazation of that protein does
change its structure and its function. When we denature a protein it's not going
to have the same function. Function for protein is dictated by
structure. Amino acid sequence, folding all these
levels of structure affect how p how protein work.
You can actually see a very easy example of how this is when you go cook a meal
leaving breakfast. Eggs are a great example, not only are
they actually the ideal protein when it comes to the contents of amino acids in
them, we'll talk about that in a moment, but eggs, when cooked, change their form.
So we can have a raw egg. That certainly looks one way or
hard-boiled egg, certainly very different structurally,
texture-wise, consistency. Different from a scrambled egg or poached
egg, different from a quiche or an omelet and different from a whipped egg.
Any two of these processes. Process is whether we boil an egg,
scramble it, fry it or whip it, we are denaturing the protein.
In. the digestion lecture.
you actually learned how proteins are broken down.
and thus. in the human body denatured.
The structure and function that the protein had in your food, whether it be,
in the egg, or amino acids in a plant, or amino acids in chicken They serve some
function in the chicken and the planter and the egg.
They could potentially serve very different function in your body once
those amino acids are taken apart, put back together, into a new protein.
The other important factor nutritionally when we talk about proteins is protein
digestibility. When it comes to protein digestibility
the type of protein is going to be important.
Not just whether it be proteins or amino acid that came from meat versus plants,
but different meats have different levels of digestibility.
Protein digestibility is not just important when it comes to breaking down,
obtaining the nutrition and amino acids we need from the meat itself, or the food
itself. But also all the nutrients that are
compounded in that protein matrix. Later we'll talk a little bit about
vitamins and minerals. One vitamin that is very affected by
protein digestibility is B12. As we get older our ability to digest
food decreases. This includes proteins.
So you might have two meal options to get B12 and protein, of course, perhaps a
steak or chicken. Now though the chicken has less vitamin
B12 in it, compared to the beef, the chicken's vitamin B12 is more digestible,
because the chicken itself is more digestible than beef.
When macro-nutrients bind micro-nutrients so when a protein finds certain minerals
or vitamins. If we can't digest the protein, we can't
create a vitamin and will not absorb or utilize that vitamin.
So we talk a little bit about protein nutrition.
When you read about protein nutrition you think about protein sources and what
other vitamins they might supply or minerals they might supply.
Keep in mind that the mineral or vitamin content of any given protein is only as
good as its digestibility. This also, of course, is going to apply
to amino acids, so when we think about how good a protein might be or protein
quality. So when we think nutritionally about
protein, digestibility is going to be very important, not only when it come to
bringing amino acids, and gaining these essential or nonessential amino acids in
our diet, but also green based vitamins, such as B12 as the example I gave.
So now, we think about amino acid content, and digestibility, we can talk
about protein quality. Now in the simplest terms, protein
quality is simply about the essential amino acid content. A complete protein
will have the perfect ratio of amino acids needed for human growth,
development and maintenance. Incomplete proteins are the one that one
or more special amino acids and these are typically plant proteins.
Animal based proteins are typically complete.
Whatever amino acid is present in lowest amounts will be considered the limiting
amino acids. They will limit the protein's capacity to
synthesize body protein. Now, if you live in a situation where you
only have one food stuff, and it is plant based, you might see imbalances in amino
acid availability and protein synthesis. But if you have some variation to your
diet, even if you have access to just rice and beans, you will get all the
amino acids that you need. If you're a vegetarian you may have heard
of terms such as complementary protein, combining foods to get all the amino
acid. And while getting all the amino acids is
very important It's not a matter of getting it in the same meal.
If you get all of the amino acids that you need on a regular basis, even if it's
a daily basis, you can say something as specific as a daily basis, you will have
the proteins, you will have the amino acids that you need to synthesize
protein. So we have the egg as our example
protein. These are the, this is the amino acid
content of an egg. The essential amino acid content.
And we can compare this ratio to other proteins to determine its quality.
There are now different analytical and laboratory methods for determining
protein quality. We can consider the chemical score.
This is the most basic analysis. This will compare the essential amino
acid content of any given protein, so perhaps some chicken, to the numerical
score generated from the ratio found in an egg.
Now chemical score does not consider digestability.
We can also measure protein quality through biological value.
Biological value's determined by nitrogen retention in animals that attest protein.
A biological value over 70% supports human growth.
We can also measure protein quality by protein efficiency ratio.
This measures weight gain in animals fed a test protein, and it is the measure
used for protein comparisons of infant formulas and baby foods.
Finally we have the protein digestiblity corrected amino acid score.
This measures essential amino acid composition.
Compared to needs, with an adjustment, for digestibility.
This measure, is what is used, to determine, percent daily value.
That's the number you see on all your food labels.
This, we are going to explore, some more in a few moments.
Alright. So let's first look at amino acid's
score. On the left you can see a list of
essential amino acids, followed by a column with our reference protein and our
test protein, which is beans. These amino acids are given in milligrams
of amino acids, program protein So in this case what's our limiting amino
acids. As we go down the list we say most of
these amino acids actually scored over one.
Our limiting amino acid is lysine. It's less than one so therefore it would
be the missing essential amino acid in this food.
Food. We can compare different scores of
different foods, so again, this is our Protein Digestibility Corrected Amino
Acid Score. Casein, eggs, and other animal based
foods are going to have a score of 1. Soy beans actually that make tofu and
tempe are very high for plants, .99, it's almost 1.
Beef is lower, so why is that? Well, there is an adjustment for digestibility.
Beef, as I mentioned a little earlier, has a lower digestibility than other
meat. So even though it is a complete protein,
so if we looked at potentially its chemical score, it would get a high
chemical score. The digestibility in beef lowers its
digestibility corrected score. As you look further down, you see the
numbers drop. Whole wheat bread, for example, has the
lowest Protein score. So let's see how this, these numbers
actually add up. So with the beef equation there you might
have expected beef to have a higher score.
Let's consider peanuts. There's the equation for the actual
score. We can see that the amino acid score that
I mentioned earlier, that's actually comparing our test protein, peanuts.
To an example protein, the egg. We'll then multiply that by its
digestibility. We take the amino acid score from the
profiled amino acids by measuring the lowest amino acid available.
So the score is going to be coming from the lowest amino acid.
In the case of peanuts the lowest amino acid score .49.
So 94% digestible so we'll multiply this times .94.
Then our final score is .46. This is not 100% digestible.
We've lowered the score relative to its lowest amino acid.
So how do we compare this to the daily value if I buy a bag of peanuts and I
look at the label? How do I know where this daily value came from? Well now we
can see percent daily value by knowing our own given daily value, the
established recommendation, and comparing that to...
The score so now we can divide the score, that final score that we get, times the
amount of protein per serving. Again when we look at daily values of a
food label they're given in servings. And divide by the daily value, again
amount of protein times the score, divided by the daily value.
So, let's say we had 7 grams of protein in our sample of peanuts.
The score was 0.46, and the daily value is 50 grams protein.
So, this amount of peanuts provides us with 6.4% of our daily value.
Of protein. Considering the amount of protein in the
food and its amino acid content and digestibility.
Alright now lets compare peanuts to another protein, something that is very
digestible and has a solid amino acid profile.
Yoghurt is a great example. It's a healthy food and it is a complete
protein. It scores one.
Highly digestible, gets us all the amino acids we need.
It provides, in a serving, 10% of our daily value of protein.
Now if we look at the amount of protein per Food, 5 g of protein in yoghurt
versus 7 g of protein in peanuts, we think hm, peanuts will give me more
protein. I need protein,
I should eat peanuts instead. But when you consider digestibility and
the amino acid profile, you see that peanuts actually provide less amino
acids, less of a daily value of proteins than yoghurt.
Certainly, you can have some peanuts with your yogurt, but if you're going to
choose one over the other, the yogurt is the more complete protein providing more
amino acids, especially essential amino acids, when we're choosing between one or
the other. So I alluded to before the concept of
vegetarianism, and combining foods to have complimentary protein.
So regardless of where your beef is, in the field or on your plate, you can eat
healthy. There's certainly numerous healthy
benefits to becoming a Vegetarian, or to simply eating a higher plant-based diet.
Plants, fruits and vegetables, are higher in fiber.
They come with a significant amount of essential vitamins and minerals.
They're lower in fats particularly saturated fat.
And while meat can be a very good part of a balanced diet it does not have to be.
And again reminding you, too, that this idea of complimentary proteins, while
certainly it is important that you eat a very Level of protein in your diet, you
eat different fruits, nuts, and seeds, beans, legumes, vegetables, whole grains.
It doesn't mean that you have to eat every single one of these, at every
single meal, to get the amino acid that you need.
When it comes to proteins and amino acids, it's the amino acids full in your
body that's important not just the stomach content.
This amino acid pool is where we get, what we need to make proteins.
Body proteins, new amino acids. To even generate glucose, glycogen and
lipids, we'll talk more about that in the metabolism section.
To make non-protein compounds that do require amino acids or nitrogen.
And then, of course, some of the amino acids from the amino acid pool will be
broken down and excreted. This pool When kept constant will always
supply the body with amino acids it needs.
So again, as long as you eat what you need to during the day, it will supply
the amino acid pool and you will be able to make the proteins you need.
Now, individuals really interested in protein generation.
Body builders, for example, that want to build large amounts of muscle mass.
Or individuals recovering from significant illness or a burn may want to
make sure that they're constantly refreshing this amino acid pool through
the diet. Why is that? Well if you need to draw
more and more out, look at the way these arrows go.
You are going to get amino acids from the breakdown of body proteins if necessary.
So, if you're trying to minimize body protein utilizations, you make amino
acids for this amino acid pool, or to break them down, eating more protein will
be protective. So, if you are a weight lifter, or
someone in hospital or you're treating someone in a hospital that has a
significant amount of tissue loss, making sure they get proteins through out the
day And really the amino acids you are looking for them to get, making sure they
get these amino acids throughout the day to keep, and you can even see some
individuals in the extreme of this that will eat every two hours even during the
night to make sure they are constantly bringing in new fresh Amino acid.
Now if we simplify this concept of amino acid pool.
We can break it down all the way to the nitrogen that's in the amino acid.
Nitrogen is what sets amino acids and proteins apart from the other Core
nutrients. Carbs and fat don't have nitrogen.
When we look at protein balance, and when I consider the protein status of an
individual, we can actually talk about nitrogen balance.
And you can read a little more about this in your text.
But to just give you a basic idea of what's happening, when we look at stasis,
or the even state, we'll be in nitrogen balance.
If we're eating more protein than we're excreting, we'll be in positive balance.
If we're excreting more protein, than we'e taking in, we'll be in negative
balance . So a healthy adult, for example not
growing any more, they'll be in equilibrium.
They'll be in balance. Someone who is growing is going to be in
positive nitrogen balance. In pregnancy, you're in positive nitrogen
balance, as well as when recovering from illness, particularly in a burn type
situation, or any illness where significant tissue damage has occurred,
and significant tissue synthesis must happen to you.
Negative nitrogen balance is when we're losing more nitrogen.
So before we get to the recovery stages of an illness, for example, we may be in
negative nitrogen balance. So that burn victim in this early stages
of synthesis is going to still be losing more dead tissue.
That dead tissue's. It's going to break down.
We're going to break down the amino acids in that tissue, the nitrogen in that
tissue. And continue to lose more nitrogen than
we are taking in. So, in certain situations we do want to
make sure we're eating more protein so that we're supplying more nitrogen to
help the healing of. Occur.
So you will see, a dietician, for example, considering protein more, in
certain individuals, that do need more nitrogen to heal.
Alright, so we know a little about proteins, in the diet.
What proteins are doing, how the amino acids are important.
But what, do proteins do? Okay, they build body tissues.
Hair, nails, skin, those are all proteins.
But proteins do other things, than just making body protein.
They're very important for all of our tissues, bones, teeth, collagen, muscle
fibers. But they're also important on their own
not just part of a muscle matrix as transporters.
Our proteins are our transporters. We talked in lipids about the cell
membrane and the importance of lipids for a healthy cell membrane.
Well proteins are also very important there.
They'll actually be the pumps. They'll be the vessels, the streets, if
you will, the pathways from one side of the cell to the other.
We can see various types, of, proteins. Pushing, components from one cell, side
of the cell to the other. What's most important here is it's the
protein that are these transporters. Insulin for example, the insulin receptor
and the insulin transporters are protein. So taking that example, the protein
function in diabetes or in blood sugar control, so the pancreas is going to
generate the insulin in response to blood sugar going up after we eat a
carbohydrate. And insulin is actually going to signal
transporters to go to the cell wall, become available to pick up glucose and
draw the glucose into the cell. Once in the cell, blood sugar lowers.
Without protein and protein insufficiency, we can't continue to
generate those transporters in cells and we can impair this process.
So protein deficiencies affect our transportation, which can effect delivery
of numerous things from one place in the body to another.
Proteins are also very important in maintaining water in right locations.
We'll talk a little bit more about that when we talk about electrolytes.
But along with electroytes, protiens are very important with attracting water Into
the cardiovascular system and keeping water where it should be, in the veins an
arteries. Someone that does have protein
insufficiency may develop edema. Edema is simply when water that's meant
to be in the vessels leaks out of these vessels and enters the body tissues and
we see swelling. And the swelling, specificically edema is
due to low protein, not keeping water, in the vac, cardiovascular system allowing
it to build up in those tissues and swell.
Proteins are also very important buffers. They can actually donate or accept
electrons to help maintain that acid base balance.
The lower the number the more acidic. The higher the number the more basic it
is. And so proteins along, and again we'll
talk about, with electrolytes are very important, buffers.
Protein is also important in glucose production and energy production.
Certain amino-acids, termed glucogenic amino-acids, are converted to pyruvate
when broken down, heated and can then be converted to glucose.
We'll talk a little bit more about this we get to metabolism.
Other amino acids, termed [UNKNOWN] are converted to Acetyl CoA when broken down,
and so they are not going to be able to be utilized in generating Glucose.
Protein deficiency is a significant problems across the globe.
Certainly, here, in the modern world, we have both protein excess, calorie excess,
malnutrition of all kind. But protein deficiency has long been a
concern for global assistance groups. Encroaching defficiency, we can see the
classical images of a child looking emaciated still somehow have that swollen
belly and feet, swollen arms, swollen hands.
This is a [UNKNOWN] So remember we said that proteins are very important at
keeping water where it belongs in the cardiovascular system.
When we don't have enough protein this water leaks out.
When we don't have enough calories, child will not thrive.
So here we see example, of not just failure to thrive, but protein and
calorie insufficiency. If we are getting enough protein, and
we're just not getting enough calories, we won't see any edema in that child.
That's a little bit about protein, so don't forget you should be reading these
chapters before you listen to my lectures, so these lectures should
certainly be building on what you've read and help tie things together.