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By Dr. Di
Pasquale
Combining
the right
foods to get
the correct
amount and
type of
protein can
be tricky.
Mauro Di
Pasquale,
M.D. gives
you tips on
what foods
you should
concentrate
on.
 In general,
proteins of
animal
origin
contain
adequate
amounts of
the
essential
amino acids
and hence
they are
known as
first class
proteins. On
the other
hand, many
proteins of
vegetable
origin are
relatively
deficient in
certain
amino acids,
notably
lysine and
the sulphur-containing
amino acids.
Mixtures of
plant
proteins can
serve as a
complete and
well-balanced
source of
amino acids
for meeting
human
physiological
requirements.
However the
combining of
right foods
is necessary
to obtain
the
necessary
levels of
both the
essential or
indispensable
and
conditionally
indispensable
amino acids.
The
essential
amino acid
lysine is
consistently
at a much
lower
concentration
in all major
plant-food
protein
groups than
in animal
foods. Since
lysine is
the limiting
amino acid,
the addition
of limited
amounts of
lysine to
cereal diets
improves
their
protein
quality.
Studies in
Peru and
Guatemala
have
demonstrated
that growing
children
benefited by
this
addition. In
addition,
the sulphur-containing
amino acids
are
distinctly
lower in
legumes and
fruits and threonine is
lower in
cereals
compared
with amounts
found in
proteins of
animal
origin.
Complementary
Proteins
- There are
important
differences
among and
between food
products of
vegetable
and animal
origin
including
the
concentrations
of proteins
and
indispensable
amino acids
that they
contain. The
concentration
of protein
and the
quality of
the protein
in some
foods of
vegetable
origin may
be too low
to make them
adequate,
sole sources
of proteins.
In some of
the poorer
parts of the
world, diets
are based
predominantly
on a single
plant (e.g.
corn) and
they
frequently
lead to
malnutrition.
Fortunately,
the amino
acid
deficiencies
in a protein
can usually
be improved
by combining
it with
another so
that the
mixture of
the two
proteins
will often
have a
higher food
value than
either one
alone. For
example,
many cereals
are low in
lysine, but
high in
methionine
and cysteine.
On the other
hand,
soybeans,
Lima beans,
and kidney
beans are
high in
lysine but
low in
methionine
and cysteine.
When eaten
together
these types
of proteins
gives a more
favorable
amino acid
profile.
Another
example
would be the
combination
of soybean,
which is low
in sulphur-containing
amino acids,
with
cottonseed,
peanut and
sesame
flour, and
cereal
grains,
which are
deficient
mainly in
lysine. In
general
oil-seed
proteins, in
particular,
soy protein,
can be used
effectively
in
combination
with most
cereal
grains to
improve the
overall
quality of
the total
protein
intake. A
combination
of soy
protein,
which is
high in
lysine, with
a cereal
that
contains a
relatively
good
concentration
of sulphur
containing
amino acids
results in a
nutritional
complementation;
the protein
quality of
the mixture
is greater
than that
for either
protein
source
alone.
Some
examples of
complementary
food
proteins
include:
- Beans and
corn (as in
tortillas)
- Rice and
black-eyed
peas
- Whole wheat
or bulgar
- Soybeans
- Sesame seeds
- Soybeans
- Peanuts
- Brown rice
- Bulgar wheat
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