Protein quality tells you how well a source supplies the amino acids your body needs. Quantity tells you how much protein you eat. You need both. A large dose of a weak source and a tiny dose of a strong source are different ways to miss the point.
Start with useful grams from a good main source. That is a better plan than treating every protein number as identical.
What complete protein means
Amino acids are the small parts that make up protein. Your body needs nine essential amino acids from food. A complete protein supplies them in useful amounts compared with human needs. [1]
Milk, whey and soy are examples of sources with a strong essential amino acid mix. The amounts are not identical, but all deserve serious attention when choosing protein foods.
An incomplete protein has a weaker supply of one or more essential amino acids. That does not make its protein fake. It means the balance needs attention.
Find the weak link
Think of building something that needs several types of part. A box full of one part does not fix a shortage of another.
Protein works in a similar way. The essential amino acid in shortest supply relative to need limits the score. Extra amounts of the others do not erase that gap.
Digestion matters too. Eating an amino acid is only useful if the body gains access to it. Our DIAAS guide explains how researchers assess that step.
Put quality and quantity together
Build each main meal around a clear protein source. Count the grams in the portion you actually eat. Then use the rest of the meal to add to that total.
Do not count a sprinkling of seeds as the main protein plan simply because seeds contain protein. The dose still has to do the work.
Research on strength training supports adequate total protein for muscle gains. It does not show that a source's impressive name replaces the need for enough grams. [2]
For a bar, apply the same logic. Check the protein amount and main source together. Quality gives the grams meaning. Quantity makes that quality useful in your day.