Nutrient Composition of Foods
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Nutrient Composition of Foods

October 9, 2019


To help us understand the content of energy
and macronutrients, as well as some micronutrients, in the food we eat, the label of every packaged
food has to carry a standardized nutrition facts panel. For fresh produce and other foods
that do not come pre-packaged, such as bananas or chicken breasts, we can refer to food composition
tables, for example the United States Department of Agriculture’s national nutrient database
for standard reference, which is available online free of charge. Nutrition facts labels indicate the nutrient
content per serving of food. While this has an obvious practical advantage, it can also
be very deceiving because your idea of a serving may largely differ from what the label says.
This bag of cheese balls snacks says it contains 9 grams of fat per serving, however it also
says that a bag contains 9 servings. Now I don’t know about you, but I for one, am
not going to eat nine times out of this bag. In fact, I could very easily eat half of it
right after I open it, so I would be getting 40 grams of fat and 675 calories.
In this course, we’ll express nutrient content as % in weight. The advantage of doing it
this way is that it’s independent of the serving size. So for example, we would say
that these chips have 32% of fat. This means that 32% of each cheese ball is made of fat.
If I eat 100 grams of them, of course I’m getting 32 grams of fat. If I eat 50 grams,
I’m getting 32% of 50, so 16 grams of fat. And if I eat 28 grams, which is what the label
says it’s one serving, then of course I’m getting 32% of 28, 9 grams of fat, like the
label says. This is the percent nutrient composition of
whole wheat bread, and this is the color code we will use throughout the course. Composition
in weight of any food is mostly accounted for by water, digestible carbohydrates, fats,
proteins, and fiber. And alcohol for alcoholic drinks. Micronutrients such as vitamins, minerals
and other phytochemicals are present in smaller amount, and in most cases account for less
than 1% of a food’s weight. As we study the different nutrients, you will learn that
in order to make an appropriate nutritional evaluation of a food, we need more details
about its composition. For example, not only the total amount of fat, but what type of
fat, not only the total amount of protein, but the quality of that protein, and of course,
not only the total amount of carbohydrate, but its composition, for example how much
simple sugar and how much starch. Also fiber content needs to be broken into soluble and
insoluble fiber. But for the time being, let’s just focus on this simple partitioning. As
you can see, 43% of the weight of whole wheat bread is accounted for by water. 34% is carbs,
13% is proteins, 7% is fiber and 3% is lipids. So, how many grams of proteins are there in
100 grams of this bread? Easy, 13% of a 100 is 13, so 13 grams of protein. But a slice
of this bread actually weighs 30 grams. So how many grams of proteins do we have in one
slice of bread? 13% of 30, so 30 divided by 100, times 13, about 4 grams of proteins. Another useful calculation that it’s often
done is looking at how much of the energy of a food comes from the different macronutrients.
This can be useful because it allows us to easily compare a food with the ideal distribution
of macronutrients in our diet, which as you’ll remember, is set in the DRIs. In this calculation,
we consider that water and fiber provide no calories, that carbs and proteins provide
4 calories per gram and that lipids provide 9 calories. For example, this is the percent
nutrient composition of whole milk. As you can see, it’s mostly water, with 4% of carbohydrates,
mostly lactose, 3% of lipids and 3% of proteins. 3% of lipids doesn’t look that much, so
why do we always say it’s better to drink low fat milk? Well, if we look at how many
of the calories from milk come from fat, we find that it’s about half, and that is a
lot. How did we calculate that? If we consider 100 grams of milk, it has 3 grams of proteins
times 4 calories per gram, so 12 calories from proteins; then 3 grams of lipids times
9 calories per gram, so 27 calories from lipids, and then 4 grams of carbs times 4 calories
per gram, so 16 calories from carbs. Water, of course, provides no calories. 12 plus 27
plus 16 is 55 calories. So 100 grams of milk provide 55 calories. 27 of these calories
come from lipids. In percent, this is 27 divided by 55, times a 100, so 49%, which is almost
half. If you consider that milk is a beverage so we can easily drink a lot – one good glass
is 250 grams, so about 8 grams of fats – AND, as we will learn, fat in milk is not of the
best quality, then yes, it is definitely better to go for the reduced fat version if you drink
milk regularly. But now let’s go back to our nutrition facts
label. This is a label for whole milk. The first information we get is the serving size,
which is considered to be one 8 fluid ounces cup. This cup, provides 146 calories, and
71 of these calories come from fat. Again, this is almost half, so the calculation we
made before was correct. A look at the nutrition facts label spares us from having to do our
own calculation every time. This cup provides 8 grams of total fat. The
label also compares this with the daily value for the average adult. These 8 grams of lipids
are 12% of the total amount of lipids an average adult should get every day.
Then, the label specifies how many of these total lipids are saturated lipids. This will
make more sense later in this course when we study the lipids. But I’m sure you know
already that saturated fats in general are not the best for your health, and two thirds
of the lipids in milk are saturated. This is at least in part what I meant before when
I said that fat in milk is not of the best quality. The label also specifies how many
trans fats are in our food, and again, this will all make sense later. Moving on, the
label tells us how much cholesterol and how much sodium are present in our milk. Then,
it shows how many total carbohydrates are in our cup of milk, 13 grams. Now, you have
to be very careful here: the nutrition facts label includes dietary fiber in the total
carbohydrates count, so these are not just the digestible carbs.
I personally think this is very confusing, but that’s how it is. Now in the case of
milk, this is meaningless because milk provides no fiber, and the sugar lactose accounts for
all those 13 grams. But if we were looking at the label of a fiber containing food, then
we would have to subtract the grams of dietary fiber from the grams of total carbs, to find
out how many digestible carbs are in there. Next, we have the total grams of proteins,
8 grams, and the content of some important micronutrients expressed as percent of the
daily value. This cup of milk covers 5% of our average daily need for vitamin A, 28%
of our need for calcium, while it doesn’t contribute to our daily need for vitamin C
or iron. This is the nutrition facts label of whole
wheat bread. The serving size is one slice. It provides 69 calories, 8 of which from fat.
Indeed, there’s only 1 gram of total fat in this slice of bread, with almost no saturated
and trans fat. I say almost because you see that curiously, these 0 grams of saturated
fat cover 1% of the daily value, this is because numbers are rounded, so that 0 is actually
zero point two. No cholesterol. 132 mg of sodium, which is not little. Then 12 grams
of total carbohydrates. 2 of these are fiber, so digestible carbohydrates are actually 12
minus 2, 10 grams. 2 of these are simple sugars, so the remaining eight are starch. We then
have 4 grams of proteins in our slice of bread, and a little calcium and iron. I’m now giving you a little assignment involving
macronutrient calculations and I strongly encourage you to try your hand at it, not
so much because you should do these kind of calculations normally, but because doing it
at least once in your life is the only way to make sure you have fully grasped the concepts
we presented over the last few videos. So, let’s make a simple sandwich with whole
wheat bread, swiss cheese and pork ham. This is the percent nutrient composition of these
three ingredients. For our sandwich, we are using 2 slices of bread, which correspond
to 60 grams, 1 slice of cheese, which is 30 grams, and 2 slices of ham, which is another
30 grams. If I have done a good job explaining over the last couple videos, you should now
be able to calculate these four things: the percent nutrient composition of your actual
sandwich (meaning, what percent of your whole sandwich is made of lipids, proteins, carbs,
water and fiber) how many total calories does your sandwich
provide what percent of this energy comes from lipids,
what from proteins and what from carbs, and how does it compare to the ideal macronutrient
distribution of diet in general After you have done your calculations, you
can find the solution by following the link below.

Only registered users can comment.

  1. Ciao! c'è un errore intorno a 4:30. Fai i calcoli considerando il 3% dei lipidi e il 4% di carbo, ma il diagramma a torta segna l' opposto: 4% sui lipidi e il 3% sulle carbo! 

    Bei video, grazie per questo corso!

  2. Insoluble proteins are originally included in total carbs on packaging labels? Is it required by law? I don’t see how producers would not subtract it themselves to lower the carb number.

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