Complete Protein
Definition
What 'Complete Protein' means
A complete protein is a protein source that provides adequate proportions of all nine essential amino acids that the human body cannot synthesize. Animal-based foods like meat, eggs, and dairy are complete, as are some plant sources such as soy, quinoa, and hemp seeds. Most other plant proteins are incomplete but can be combined to form complete profiles.
Related terms
In depth
The longer answer
A complete protein is a dietary protein that contains all nine essential amino acids in sufficient amounts for human health. These amino acids cannot be synthesized by the body and must come from food. The concept is most commonly encountered in discussions of animal versus plant proteins, where meat, eggs, and dairy are often described as complete, while many plant sources are considered incomplete.
In practice, the completeness of a protein depends on its amino acid profile. Animal-based foods like chicken, fish, and eggs naturally provide all essential amino acids in ratios that meet human needs. Most plant proteins, such as beans, grains, and nuts, are low in one or more essential amino acids, typically lysine or methionine. However, combining complementary plant sources—like rice and beans—can create a complete amino acid profile without animal products.
For someone eating a varied plant-based diet, the concept of complete protein is largely outdated. The body maintains a pool of amino acids from meals throughout the day, so it does not require each meal to be complete. As long as overall energy and protein intake are adequate, and a variety of plant foods are consumed, essential amino acid needs are easily met. The main limitation is for those relying heavily on a single plant food, like only wheat or only corn.
At a glance
Quick facts
| Detail | What to know |
|---|---|
| Essential amino acids | 9 total: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine |
| Common complete sources | Soy, quinoa, amaranth, hemp seeds, chia seeds |
| Animal sources | Meat, poultry, fish, eggs, dairy products |
| Complementary pair example | Rice and beans, hummus and pita |
In practice
What this means for you
- When shopping, look for whole plant proteins like tofu, tempeh, or edamame, which are naturally complete without combining.
- If eating a varied diet with legumes, grains, nuts, and vegetables, you do not need to worry about protein combining at each meal.
- For athletes or those with higher protein needs, include a complete plant protein like soy or quinoa in at least one daily meal.
- When reading labels, check for added amino acids in processed vegan products, but know that whole foods are generally sufficient.
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