A complete protein is a protein source that contains all nine essential amino acids in sufficient quantities. These amino acids are deemed "essential" because the human body cannot synthesize them on its own, and therefore they must be obtained through diet.
Understanding Amino Acids and Protein Quality
Proteins are built from building blocks called amino acids. There are 20 amino acids in total that the body uses to create proteins. Nine of these are essential:
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
A protein source is considered "complete" when it provides adequate amounts of all nine of these essential amino acids. If a protein source is lacking or low in one or more essential amino acids, it's considered an "incomplete protein."
Sources of Complete Proteins
Generally, animal-based protein sources are complete proteins. Some notable examples include:
- Meat: Beef, pork, lamb, etc.
- Poultry: Chicken, turkey, duck
- Fish and Seafood: Salmon, tuna, shrimp, etc.
- Eggs
- Dairy Products: Milk, yogurt, cheese
Plant-Based Complete Proteins
While many plant-based proteins are incomplete, there are some exceptions:
- Quinoa: A grain-like seed that's a complete protein.
- Soy: Soybeans and products made from soy (tofu, tempeh, edamame) are complete proteins.
- Hemp Seeds: These seeds offer a complete amino acid profile.
Complementary Proteins
Even if you primarily consume incomplete proteins, you can still obtain all the essential amino acids by combining different plant-based foods throughout the day. This is known as "complementary proteins." For example:
- Combining beans (low in methionine) with rice (low in lysine) provides a complete amino acid profile.
- Peanut butter on whole wheat bread is another classic example.
Why Complete Proteins Matter
Consuming adequate amounts of complete proteins (or strategically combining incomplete proteins) is vital for various bodily functions, including:
- Muscle growth and repair
- Enzyme production
- Hormone regulation
- Immune system function
In summary, a complete protein is a protein source containing all nine essential amino acids in sufficient quantities to support human health. While animal products are generally complete protein sources, certain plant-based options and complementary protein combinations can also fulfill these requirements.
