Proteins: "How will I get enough?"

A diet without meat can provide enough proteins.
We usually think that meat and animal products are the only source of proteins. It is not true; a plant-based diet can easily meet our requirements, as long as you consume adequate amounts of calories.

What is a protein?
Proteins are made up of 20 different amino acids.
They are part of all our body tissues (skin, muscles...), organs (liver, kidney...), liquids (blood, saliva, etc... except urine and bile).
Once absorbed, proteins are broken down into amino acids from which they will be rebuilt in our cells.

Nine amino acids can not be synthesized by our body. They are called Essential Amino Acids and must be supplied daily. In parenthesis are the conditionnally essential amino acids.

Those Essential Amino Acids are:
Phenylalanine (+ tyrosine)
Methionine (+ cystein)

Protein combining
Plant proteins can provide adequate amounts of every one of the amino acids we require. Contrary to animal proteins which contain all 9 amino acids in the same food, some plant proteins, except for soybeans, are a little short in some of them.
Animal proteins are called "complete" whereas plant proteins are called "incomplete".
Cereals are short in lysine and legumes are poor in methionine.

We say that lysine is the limiting amino acid in cereals whereas methionine is the limiting amino acids in legumes.

A limiting amino acid in a protein limits the absorption of the other amino acids in the same protein.

When a food is lacking one or several amino acids, it can be eaten with another food that is rich in these missing amino-acids and the complementary is done. We got a complete protein.

Any legume pairs up perfectly with any grain, nut or seed to make a complete protein.

Examples: Lentils and rice
Couscous and garbanzo beans
Kidney beans with tortillas

Recent studies suggest that you do not have to combine proteins in the same meal. The complementary can be done throughout the day.
If you follow the food vegetarian food guide pyramid you will easily meet your daily proteins requirements.

Protein digestibility
It depends on how easily a protein is broken down to its amino acids.
Animal proteins are 95 % digestible whereas plant proteins are 85 % digestible.

However, cooking methods (simmering, boiling, soaking) tend to increase the digestibility of the protein.

Excess proteins
People usually tend to eat too much protein, especially animal proteins which are not healthy.
Too much protein can cause people to excrete excess amounts of calcium through their urine, increasing risk of kidney stones and osteoporosis.

Realized by Laurence LIVERNAIS-SAETTEL, dietetian
© Copyright L. Livernais-Saettel 2000
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