Proteins in food, and the trick of complementarity
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Proteins in food, and the trick of complementarity

October 12, 2019


Animal food in general is a good source of
protein because it has a lot of highly bioavailable proteins and it also has a very high protein
quality, all the essential amino acids we need, and in the right proportions. If you think about it, our requirement for
amino acids roughly reflects the amino acidic composition of our body, because in the end
that is what we need to build and maintain our tissues. So it makes sense that animal food has a high
protein quality for us, because its composition is similar to ourselves. If we were cannibals, we would probably say
that human meat has the highest protein quality for humans. But since luckily we don’t eat each other,
then the next closest thing we have is turning to other animal sources of protein. The numbers you see here are percent weight. So one hundred grams of eggs contain about
13 grams of protein. Meat, 15 to 20%. Fish about the same, tuna has a little bit
more. Milk and yogurt, 3%. It doesn’t look much but remember that they
have a lot of water, so if we look at how much of their energy comes from protein, that’s
actually quite a lot. Cheese concentrates that protein, up to 25
to 35%. However, like we said at the beginning of
our protein section, animal food is not the only source of proteins. Nuts and seeds for example are very good sources
of protein. They have between 20 and 26 grams of protein
per 100 grams, and a pretty good protein quality, not as good as the animal sources, they could
use a touch of extra lysine, but overall it’s very good. However they are very energy dense foods,
so we can only eat so much and we certainly couldn’t get all of our proteins from them. We can get some from cereals. As long as they are whole grains, they also
have quite a lot of protein. Not as much as nuts and seeds, but keep in
mind that we eat more. A serving of pasta is of course bigger than
a serving of sunflower seeds. They also have a composition that’s surprisingly
close to the animal sources of protein, however they have one big problem. They have only one third of the lysine we
need, and this dramatically lowers their protein quality. This means that if we were to eat only cereals
as our sources of protein, we would not be able to use most of that protein because it
lacks this one essential amino acid. The protein content of whole grain cereals
is between 8 and 15%, oats being the richest source. The pseudo-cereals quinoa and amaranth also
have a little bit more and they also have more lysine, so their protein quality is slightly
better too. And then we have legumes. Legumes also have a very good protein content,
much higher than cereals, ranging between 20 and 26%. But legumes also have a problem of protein
quality. The lacking amino acids this time are the
sulfur-containing ones, Methionine which is essential and Cysteine which is conditionally
essential. So just like cereals, we could not rely on
legumes alone as protein sources in our diet. Soy and soy products are exceptional sources
of vegetable protein, with 36% that ends up being even more than meat. Besides having higher protein content, they
also have more methionine and cysteine ant thus a much better protein quality compared
to the other legumes. Many nutritionists actually consider soy protein
to be complete. Fruits and vegetables have good protein quality,
but they have very low protein amounts, fruit is less than 1%, vegetables are slightly higher,
but still less than 3%, so they certainly contribute to our protein requirement, but
we could never get all the protein we need from vegetables alone. We’d need to eat tons. And then we have some alternative sources
of proteins: tofu from soy, tempeh from soy, quorn from a fungus that has a lot of fairly
good protein, seitan made from wheat’s gluten, protein isolates, such as milk’s whey proteins,
egg whites, and soy, and then let’s not forget that in other parts of the world people
will eat insects, so this is mealworm, and here a picture from a vietnamese market where
instead of chicken breast you have bugs, larvae and insects, good sources of protein, cheap
and pretty much tasteless. One important concept that we need to understand
is that of complementary proteins. We have just surveyed protein content and
quality of different food sources, and we said ok these are high quality, these are
low quality sources of proteins, but let’s not forget that the protein quality of foods
individually is only marginally relevant. When we eat, we don’t really care about
the protein quality of a single food, what we care about is the protein quality of the
whole meal, so the combination of food that we eat. And so if we combine two our more low quality
protein sources in the right way, and if we eat them together, not necessarily in the
same dish, but at the same meal, then we can compensate for essential amino acid deficiencies
and come up with a high protein quality meal. To clarify this very important concept, let’s
make a little example. Imagine one more time that we need to build
our little tripeptide, a protein made of three amino acids. And this time I didn’t even write the names,
we just have the colors: we need to build a protein made with one green amino acid,
one orange amino acid and one blue amino acid. And now imagine we have this food, food one,
that contains thirty amino acids: ten green, ten orange and ten blue. How many copies of our protein can we build
with this pool of amino acids? Well, pretty easy. We can build ten. Right? We take one, one and one, for ten times. So we can make ten copies of the protein that
we need, so we could say that the protein “value” of this food is 10. This food is a high quality protein food,
because it has all the amino acids that we need, in just the right proportions. We will be able to use all of them, and make
the protein that we need. But now imagine that we ate another food,
food 2. Now, the proportions of the different amino
acids have changed. This time we have 10 green amino acids, 18
orange, and 2 blue. Notice that the total protein content is the
same as food 1, we still have 30 amino acids. So the “grams” of total protein in these
two foods would be the same. But now, how many copies of our protein can
we build? Obviously, we can only make two, because after
that we will be out of the blue amino acid and we will not be able to build any more
copies of the protein that we need. So we will build only two copies, we can say
that the protein value of this food is only two, and that “blue” is the limiting amino
acid. We don’t have enough to keep going with
our protein synthesis. On top of that, we are left with 8 green and
16 orange amino acids. But because we don’t have any way to store
extra amino acids, we will have to throw them away, by using them for energy or converting
them to fat. And now let’s consider food 3. Again, the total amount of protein is the
same, we still have 30 amino acids, but now we have a lot of blue and only 2 of the orange
amino acid. Again, we can only make two copies of our
protein, then this time the orange will become limiting, and we will have to throw away 8
green and 16 blue amino acids. The protein value of food 3 is also only two. So same protein content as food 1, but much
lower quality. But now imagine that we eat food 2 and food
3 together, and I halved the amounts of each because I want the total protein content to
stay the same. So we eat half the amount of food 2 and half
the amount of food 3, and again we have thirty amino acids total. But now, the lack of orange in food 3 will
be compensated by food 2, and the lack of blue in food 2 will be compensated by food
3. So how many copies of our protein can we now
build? We have 10 green, 10 orange, and 10 blue amino
acids, so now we can again build 10 copies of our protein, and we don’t have anything
to discard. Because of the way these two low quality foods
mutually integrate each other, they complement each other and result in a high protein quality
meal. The protein value of the combination of these
two foods is now ten. Notice that 10 is more than just the sum of
the individual protein values of the single foods. If we had eaten one at lunch and one at dinner,
the total protein quality would have only been two plus two, four. But by eating them together, because of the
way the integrate each other, then we have a much higher protein value. The most important practical application of
this concept is the combination of cereals and legumes, the typical case of complementary
proteins. Remember how we said that cereals have a very
good proportion of amino acids except for one, they lack lysine. But they have a lot of methionine and cysteine. Instead legumes they have low methionine and
cysteine, but they have all the lysine. If we eat them together in the right proportions,
which is about two thirds cereals and one third legumes, they complement each other
and provide all the amino acids we need. So if I eat them alone, if I only eat a slice
of whole wheat bread or if I only eat a spoon of chickpeas hummus the protein quality would
be low. But if I put my hummus on my slice of bread,
then they will complement each other and I will have the same protein quality than I
would have had with a steak. Since we are talking hummus, another good
way to complement it is to add sesame paste to the hummus itself.

Only registered users can comment.

  1. Hi Stefano and thanks a lot for your videos.

    All the things you talk about in this video are clear and useful but I've a question about the % of protein. If the food A has 10 gr. of proteins and the food B has 15 gr. of proteins, and they can perfectly combine each other thanks to the amino acids, how many gr. of higly biological value of proteins will I have for my meal? 25? 12,50?

    Thanks, and sorry for my bad english. πŸ™

  2. Truly a well done video. Translating a large amount of knowledge into a video that is concise and very easy to follow.

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