You may have heard the term complete protein. What does it mean, and is it something you should be worrying about?
What you need to know
Protein is made up of smaller building blocks called amino acids. There are 21 different amino acids that can be combined in endless variations to comprise a protein. Did someone mention Lego?
The human digestive tract breaks a protein apart into individual amino acids and then uses them to build up tissues, such as muscles.
Essential Amino Acids cannot be synthesized by the human body on its own; they must be obtained from an external source – food. Non-essential amino acids can be synthesized in the body by using essential amino acids. Essential amino acids are sometimes referred to as Indispensable amino acids.
9 of 21 amino acids are considered essential: leucine, isoleucine, valine, lysine, threonine, tryptophan, methionine, phenylalanine, and histidine.
The non-essential amino acids are alanine, asparagine, aspartic acid, glutamic acid, arginine, cysteine, glutamine, glycine, proline, serine, and tyrosine.
Every food we eat has a different amino acid profile, meaning that it has a different percentage of essential amino acids.
A food with a protein profile that includes all 9 essential amino acids is called a complete protein.
Protein from individual animal sources such as red meat, poultry, dairy, and eggs, is always complete protein.
Protein from plants may be complete proteins, but in many cases they contain low levels of some essential amino acids. In some cases, plant proteins are incomplete, for example fruits and yams.
In the past, vegetarians were advised to carefully plan each meal to combine grains, legumes, and veggies. This would achieve the right amino acid mix in order to assure that the meal included complete proteins. We now know that this is not required, as long as in the course of a day (24 hours) a person consumes a variety of foods.
Many traditional non-meat dishes achieved a complete protein profile thousand of years before nutrition science was ever invented. Examples include rice and bean combos in most of Asia, or corn and bean dishes in Central America. Basically any legume and grain combo works.
Worldwide, 60% of people’s protein intake is from plant based foods. In the US, only 30% of the protein intake is from plants; the rest – 70% – is from animal sources.
If you live in America, vegetarian or omnivore, you don’t need to worry about your protein intake. It is almost guaranteed to be complete protein.
1. Protein basics – Center for Disease Control and Prevention
2. Protein and Amino Acid Requirements in Human Nutrition – The World Health Organization, 2002