Two foods with 20g of protein are not necessarily equal. What the column in our tables cannot tell you.
Every table on this site shows a Protein column, in grams per 100g. That figure is accurate, and it is useful. But it measures a mass, not a usefulness.
In other words, it answers “how much is there?” and not “what can my body do with it?”. Those are two different questions, and the gap between them can be considerable.
It is the same mechanism described in Hidden carbs: the printed number is not wrong, it simply does not say what we think it says.
A protein is not a single substance. It is an assembly of amino acids, about twenty of them, linked in a precise order. Eating a protein therefore means swallowing a chain that digestion takes apart into loose pieces, before the body reassembles its own proteins from them.
Of those twenty or so, the body can make some itself. Nine, it cannot. Those have to come from food, every day, without exception. They are called the essential amino acids.
Tryptophan is highlighted because it comes up elsewhere on this site: it is what the body makes serotonin from, and then melatonin. It is the link to Sleeping better.
💡 The useful image is a construction set. Having a thousand bricks matters little if the ones of a single shape are missing: the model stays unfinished, and the spare bricks are of no use.
A food in which all nine essentials are present in sufficient proportions provides what is called a complete protein. That is the case for almost every animal source: eggs, fish, meat, dairy.
Plant sources are almost all short on one or two amino acids, and very consistently so:
This is what is called the limiting amino acid: the one that, being in short supply, caps the use of all the others. Hence the weak link analogy, or the barrel whose shortest stave sets the level.
The important point, and often the misunderstood one: the two shortfalls are complementary. Grains bring the methionine legumes lack, legumes bring the lysine grains lack. Together, the profile becomes complete again.
Couscous and chickpeas, rice and lentils, bread and hummus, corn and black beans: every traditional cuisine found this pairing long before anyone could explain it.
Soy is the exception among plants, with a profile close to complete on its own.
There is an official measure, recommended by the FAO since 2013: DIAAS, the Digestible Indispensable Amino Acid Score. It combines two things the “protein” column ignores, both of them.
First the profile: does the food contain the nine essentials in the right proportions? Then digestibility, measured amino acid by amino acid rather than on the protein as a block. Because a protein can be well composed and poorly absorbed, which amounts to the same thing on the plate.
The three categories used by the FAO
Without going into food-by-food values, the ranking is consistent: egg and dairy proteins sit at the top, meat and fish just behind, soy and legumes in the middle, and grains well below the 75 threshold.
This score appears on no packaging in France, and in no table on this site. That is precisely why this article exists: the information is not available to you at the moment you are comparing two products.
The good news is that none of this requires you to calculate anything.
If you eat animal products, the question is settled.
Eggs, fish, meat and dairy all provide complete profiles. Our tables' “Protein” column is then enough to compare: see Meat, Fish and Dairy & eggs.
On a plant-based diet, combine rather than pile up.
A grain with a legume on the same day is enough. They do not need to be on the same plate, contrary to what was long claimed: the body holds a pool of amino acids that absorbs the gap.
Be wary of the word “protein” on a package.
A cereal bar can advertise 10g of protein without that protein having a usable profile, and most often with the carb load described in Hidden carbs.
Count foods, not grams.
Two or three different sources across the day settle the profile question far more reliably than a total to hit. The macro calculator is still useful for quantity, it simply says nothing about quality.
| Idea | What it actually tells you |
|---|---|
| The “Protein” column | A mass. Neither the amino acid profile nor the share actually absorbed |
| Complete protein | All nine essentials present in sufficient proportions. Almost everything animal, plus soy |
| Limiting amino acid | The one that is missing and caps the use of the others. Lysine for grains, methionine for legumes |
| DIAAS | The FAO measure combining profile and digestibility. Absent from labels |
| “High in protein” | A quantity, never a quality |
The thread running through this site: an accurate number can mislead, not because it lies, but because it answers a different question from the one being asked.
ℹ️ Sources
• Method and thresholds: Dietary protein quality evaluation in human nutrition, FAO Food and Nutrition Paper 92, 2013. Full report (PDF)
• Ten years on: Digestible indispensable amino acid score (DIAAS): 10 years on. PubMed Central
• Plant versus animal comparison: Comprehensive overview of the quality of plant- and animal-sourced proteins based on the DIAAS. PubMed Central