Complete vs Incomplete Protein: Does the Difference Matter?
The complete versus incomplete protein distinction is one of the most repeated pieces of nutrition advice, and one of the most misunderstood. Here is what it actually means and how much it matters.
What essential amino acids are
Proteins are made of amino acids. Of the 20, nine are essential: your body cannot synthesise them from other compounds and must obtain them from food. A complete protein contains all nine in sufficient quantity to support the body's needs. An incomplete protein is low or deficient in at least one.
Which foods are complete proteins
- Animal sources (complete): eggs, meat, poultry, fish, dairy.
- Plant sources that are complete: soy and soy products (tofu, edamame, tempeh), quinoa, buckwheat, hemp seeds.
- Most other plant proteins are incomplete: legumes, most grains, nuts and seeds each lack or are low in one or more essential amino acids.
How incomplete proteins become complete in practice
The original advice was to combine complementary proteins at each meal, such as rice and beans, to create a complete amino acid profile. Current evidence shows that spreading complementary plant proteins across the day, not necessarily at the same meal, is sufficient. The body maintains a pool of amino acids that can be topped up across meals.
Does this matter if you eat a varied diet?
For omnivores eating meat, dairy and eggs, the complete versus incomplete distinction is largely irrelevant: the diet covers all nine essentials routinely. For vegetarians and vegans, variety matters: eating only one type of plant protein, such as only rice, would eventually leave the diet short in lysine. A varied plant-based diet with legumes, grains and seeds almost always covers all nine.
Tracking your intake
Hitting total protein targets matters more for most people than obsessing over amino acid profiles. Protein Tracker logs your daily intake and shows progress toward your goal. For a list of the most protein-rich sources, see best high-protein foods.
Common questions
- What is a complete protein?
- A protein source that contains all nine essential amino acids in adequate amounts. Most animal proteins are complete. Plant proteins that are also complete include soy products, quinoa, buckwheat and hemp seeds.
- Do you need to combine incomplete proteins at every meal?
- No. Eating a variety of plant proteins across the day is sufficient. The body maintains an amino acid pool that is topped up gradually, so complementary proteins do not need to be eaten at the same meal.
- Is plant protein as good as animal protein?
- Plant proteins are generally absorbed at a slightly lower rate than animal proteins, and most individual plant sources are incomplete. A varied plant-based diet that includes legumes, grains, nuts and seeds covers all essential amino acids and can support muscle growth and general health.