The proportions of essential amino
acids in food products may differ from those required
by the body to synthesize the proteins. The proportion
of each essential amino acid in the food products
that contain proteins determines the quality of them.
Those food proteins found in the essential amino
acids required by the organism are considered to
be high-quality or high-biological-value proteins.
If there is a low quantity of one of the essential
amino acids in the protein, this is a low-quality
or low-biological-value protein. The scarcest amino
acid is called “limiting amino acid”.
The limiting amino acid tends to vary according
to the various proteins. This means that when two
different foods are combined, the amino acids of
one protein can compensate for those the other one
lacks. This is called “protein complementation”.
The act of combining vegetable proteins such as a
cereal with a legume results in a high-quality protein
that is as good as, and in some cases better than,
an animal protein.
Grains and legumes are good examples of it. They
contain all the amino acids we have already mentioned,
even though cereals lack “lysine” and
soy lacks an adequate proportion of “methionine”.
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