Protein (or rather, amino acid) requirements
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The amount of protein needed in one's diet requires consideration. This is
because it's not so much the protein we require, but the amino acids that the protein source
in question contains. Since different
proteins contain different percentages of the 20 biologically active amino acids,
logic would tell us that depending on the types of food we eat, we will get
varying percentages of amino acids. What's the significance here? Protein
can be categorized according to its biological value. The higher the biological
value of a protein, the higher the amount of essential amino acids it contains.
Of course, all proteins contain amino acids, but certain proteins contain more of the
types of amino acids we need. Meats and eggs are primary examples. If more
meats are included in the diet, the less the requirement for protein. This is
because meats and eggs contain the essential amino acids in similar proportion
for synthesis of human tissues.
Plant proteins, on average, have a lower biological value in comparison to
animal (meat) proteins. Since a vegetarian diet excludes meat products, one
can compensate by combining plant products of different biological values to
supply the body with appropriate amounts of essential amino acids. For example,
kidney beans are rich in the amino acid lysine, but low in percentage of the
amino acid methionine. Maze contains a high percentage of methionine, but a
low percentage of lysine. We can see that by combining these two plant
products completes part of the diet in regards to protein.
Now that we have some insight into the composition of proteins, how much
protein do we need? It is safe to say that the average individual requires
approximately just under a gram of protein per kilgram of body weight. This means
that a woman weighing in at about 50kg (roughly 111 lbs.) requires between 40-50 grams
of protein per day. The protein required should be of mixed biological value. This
is why a balanced diet is important (since different foods contain different percentages
of amino acids). Individuals with more physical demands on the body requure more protein.
A person who exercises vigorously obviously requires more protein, since they are
damaging tissues while exercising. To build muscle as well, one needs to have a
positive nitrogen balance. Nitrogen balance takes place when the amount of nitrogen
consumed equals the amount passed in the urine, faeces, and sweat. Note that nitrogen
is a breakdown product of protein, so this is a good indicator if an individual
is getting enough in the diet. Positive nitrogen balance is when nitrogen intake
is greater than excretion. We can see this when children grow, when we build muscle in
the gym, in pregnancy, and recovery from illness, surgery, etc. Negative nitrogen
balance is when nitrogen excretion exceeds intake. We can witness this during times
of stress, starvation, injury, illness, etc.
Protein requirement also changes depending on the amount of carbohydrates we include in
the diet. Carbohydrates are required as a fuel source. When deficient of adequate
carbohydrates, amino acids are used for the production of glucose. This is why diets
suggesting low carbs are to be considered carefully. Glucose is the primary fuel of
the brain and without it, signicant damage and even death can occur. As we can see,
there are many factors to consider when dieting, or attempting to alter
any aspect of the metabolism.
learn about the individual amino acids