Protein quality – why not every protein truly nourishes your body

You eat enough protein – and yet your muscles, energy or recovery are falling behind? Then the problem may lie not in the quantity, but in the quality of the protein.

Proteins are, among other things, the building materials of your body – for muscles, enzymes, hormones, your immune system. But: only when the protein from your food contains the right amino acids in a usable form can your body actually use these building blocks.

Not all protein is created equal – what really matters

For your body to truly use protein – e.g. for muscles, enzymes or hormones – two things must be right:

Amino acid profile – the right building blocks

A protein is only «complete» when it contains all essential amino acids (EAAs) – that is, those your body cannot produce itself. If even one of them is missing or present in too small an amount (this is called a limiting amino acid), the entire protein can only be partially utilised.

Comparison: Imagine you want to build a house and have everything – bricks, windows, doors – but no roof tiles. Then the rest is of no use to you either, because the house stays incomplete. That’s how it goes for your body with a patchy amino acid profile: it cannot incorporate the protein meaningfully – and, if necessary, uses it for energy production instead of building.

Digestibility & absorption – what actually arrives

Not everything on your plate ends up in your cells. Especially plant proteins are often harder to digest, as they are surrounded by fibre, antinutrients or plant cell walls. What is decisive is how much of the protein is actually absorbed in the small intestine.

Comparison: You order a parcel with valuable components – but it stays with the neighbour in the stairwell. It has indeed been bought, but has not arrived. That’s exactly how it is with poorly digestible protein: it’s on the packaging, but your body doesn’t get it.

👉 That’s why: just because something contains «a lot of protein» by no means guarantees that your body can fully use it. What is decisive is the combination of amino acid profile and digestibility – that is, the actual quality of the protein.

From outdated methods to modern measurement: PDCAAS vs. DIAAS

How is PDCAAS measured?

PDCAAS = Protein Digestibility Corrected Amino Acid Score

➤ What is done?

1. Analysis of the amino acid profile of a food: one looks at whether the protein contains all essential amino acids – that is, those the body cannot produce itself.
2. Estimating digestibility: one measures in the stool how much nitrogen (= an indicator of undigested proteins/amino acids) is excreted again.
3. From this an overall score is calculated:

PDCAAS = (content of the limiting amino acid) × (digestibility of the total protein)

Important: digestibility is calculated here on a flat-rate basis using the total protein – not at the level of individual amino acids. And the measurement is taken after the large intestine – that is, at the end of digestion.

What is the problem with this method?

• The body does not absorb proteins and amino acids in the large intestine, but in the small intestine.
• And PDCAAS does not distinguish whether, e.g., a certain amino acid is indeed present but poorly absorbed.

What does «being absorbed less well» mean?

When one says that plant proteins are absorbed less well, this means:

They (plant proteins) are indeed there – but the small intestine cannot utilise them fully.

Why?

• Fibre can «lock in» proteins, so that enzymes cannot reach them.
• Antinutrients like tannins or phytates inhibit digestion.
• Or the amino acids are in a hard-to-access structure (e.g. in grains of cereal).

This leads to a portion of the amino acids not being absorbed into the blood, but remaining unused.

And what happens to these unabsorbed amino acids?

If they were not absorbed, they move on into the large intestine. There, the following happens:

• They are broken down by gut bacteria (fermented or «metabolised»).
• In the process, gases (e.g. ammonia, sulphur compounds) and other metabolic products are formed.
• These no longer have any nutritional value for you – they are lost or can even be a burden.

How is DIAAS measured?

DIAAS = Digestible Indispensable Amino Acid Score

➤ What is done?

1. Each individual essential amino acid in the food is measured.
2. Then one tracks how much of it was actually absorbed in the last section of the small intestine (ileum).
3. From this an individual utilisation value is calculated per amino acid – more precise than PDCAAS.

➤ How is this measured?

• In studies (especially with animals such as pigs), an artificial outlet is placed at the end of the small intestine («ileal cannula») in order to take samples directly there – before the digestive residues reach the large intestine.
• This shows what was really absorbed – and what simply «slipped through», even though it doesn’t appear later in the stool (because it was, e.g., broken down by bacteria in the large intestine).

Why is this measurement better than PDCAAS?

Because it is no longer just about what is theoretically there, but:

👉 What of it the body can really absorb and use.

It’s as if, after shopping, you didn’t just count how many packs you bought – but checked whether they are open, usable and fresh.

👉 Only what arrives in the small intestine and is utilised truly nourishes your body. Everything else does remain in the digestive tract – but doesn’t help you with muscle building, the immune system or cell repair.

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DIAAS values explained simply – here’s how to read them correctly:

🔹 > 1.00 = top quality The protein is not only complete but is also absorbed almost entirely. 👉 Your body can use nearly all of it. Example: milk, egg

🔹 0.75–1.00 = solid quality The protein is well usable, but not quite perfect. 👉 A large part arrives – a small part falls behind. Example: meat, fish, some legumes (e.g. cooked beans)

🔹 < 0.75 = limited quality The protein is incomplete or poorly available. 👉 On paper it looks good, but your body can use only little of it. Example: many plant proteins without a matching combination (e.g. only rice or only peas)

💡 Remember: DIAAS shows not only how much protein is in it – but how much of it your body can really use as building material. Or, put differently: just because a protein is in the food by no means means it arrives in your body.

DIAAS in practice: why animal proteins are usually in the lead

The DIAAS figures show clearly: animal proteins your body can as a rule utilise better than plant ones. This is simply because they:

• contain a complete amino acid profile
• and can be digested and absorbed far better and more holistically

A simple example: If you want to get 20 g of truly usable protein, you have several options:

• You can e.g. eat 100 g of cooked beef – this provides you with the necessary amount of high-quality, directly usable protein with relatively few calories.
• Or you take a small portion of whey protein – about 25 g of powder.

But: if you try to cover these 20 g via plant sources such as kidney beans or peanuts, you need either over 600 g of beans or 170 g of peanuts. That not only sounds like a lot – it is. And: in doing so you take in significantly more calories and carbohydrates. The reason is simple – your body can draw from these plant proteins less usable protein. The modern measurement method DIAAS shows this very clearly. The older method PDCAAS often overestimated plant protein sources, because it only measured what did not end up in the stool – but not what is really absorbed and arrives in the body.

If you eat plant-based or vegan:

Then combination and planning matter particularly – because many plant proteins are not complete, which means: they are missing one or more essential amino acids that your body cannot produce itself. In addition, they are often utilised less well – so your body can absorb and use less of them.

But with a few tricks this can be compensated for well:

• Combine cleverly: by combining different plant proteins you can supplement amino acids in a targeted way. Together this creates a more complete profile – even if the individual source isn’t enough. 👉 Classics: rice + beans, lentils + millet, peas + corn Rule of thumb: legumes + cereals or nuts often complement each other ideally. But be aware: depending on the combination, the carbohydrate intake.
• Use plant protein isolates or concentrates in a targeted way: products from pea, rice, hemp or soy isolate often have far better DIAAS values than whole foods – they thus provide concentrated, more usable protein without too many calories or carbohydrates. What long-term influence these highly processed products have on health is, however, still unclear.
• Prepare fibre-rich sources consciously: soaking, sprouting or fermenting (e.g. with tempeh) improves the availability of the amino acids – and reduces antinutritive substances that inhibit absorption.
• Spread your protein across several meals: plant protein often acts more slowly or more incompletely in the body. It therefore pays to plan several small protein portions spread over the day – ideally with 25–30 g per main meal.

💡 Extra tip: If you are athletically active or want to build muscle specifically, a vegan shake made from pea and rice protein can be a clever addition – together the two make an almost complete amino acid profile.

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Conclusion: what counts isn’t how much – but what your body can really utilise

You can eat large amounts of protein – but if your body cannot absorb and utilise it properly, it remains largely ineffective. The result: less recovery, less muscle building, less enzyme activity – and often more cravings and fatigue, despite a seemingly sufficient intake.

👉 Quality beats quantity.

That’s why it pays to look more closely at protein:

• DIAAS instead of PDCAAS: only the modern DIAAS value shows how much protein actually arrives in the body – and not just what is theoretically in the food. • Amino acid profile + utilisability are decisive: essential amino acids must be present in sufficient amount and form – and be well available. • Animal proteins usually deliver a complete overall package – plant sources need targeted combinations and planning in order to be equivalent.

In the end, what counts isn’t what’s on the packaging – but what arrives in your cells. And that often makes the difference between standstill and progress, between exhaustion and real energy.