Not All Protein Is Equal: What the DIAAS Score Changes About How You Count Your Grams
57% of consumers plan to increase their protein intake in 2026. The updated guidelines say 1.2-1.6g/kg. But this conversation often misses a critical point: not all grams of protein are equivalent.
The DIAAS (Digestible Indispensable Amino Acid Score) is the most precise measure of protein quality available today, recognized by the FAO and WHO. And it changes how we should think about protein consumption.
How DIAAS works
DIAAS measures two things simultaneously:
- Protein digestibility (what proportion is actually absorbed at the small intestine level)
- Indispensable amino acid composition (the 9 amino acids the body can't synthesize on its own)
A score of 1.0 or higher means the protein is complete and highly digestible. Below 1.0, there's either limited digestibility or limiting amino acids.
The scores that matter
Here are DIAAS scores for major protein sources:
- Whey protein: ~1.25 — the highest score across all sources
- Whole egg: ~1.18
- Casein: ~1.08
- Chicken: ~1.05
- Beef: ~1.00
- Soy: ~0.78-0.98 depending on form
- Pea protein: ~0.82
- Brown rice: ~0.59
In practice: if you consume 30g of pea protein, the effect on muscle protein synthesis is lower than 30g of whey, because of lower digestibility and a less complete amino acid profile. If you're navigating choosing between protein powder types, DIAAS scores are one of the most useful tools available.
Leucine: the amino acid that triggers synthesis
For muscle protein synthesis specifically, leucine is the most critical limiting amino acid. It acts as a signal to activate protein synthesis. Whey and eggs are leucine-rich. Most plant proteins contain less, which partly explains their lower DIAAS score.
If you're vegetarian or vegan
The individual DIAAS of plant proteins is often below 1.0 — but combining sources compensates. Rice + legumes, soy + grains: the limiting amino acids of one source are compensated by the other. The solution isn't to avoid plant proteins — it's to combine them and slightly increase total dose (20-30% above standard recommendations).
What this changes for you
If you're targeting the right daily protein intake to build muscle and relying mainly on lower-DIAAS plant sources, you should aim higher — 1.8-2.0g/kg — to get equivalent muscle protein synthesis effects. That's not a reason to eat only whey and eggs. It's a reason to understand what you're consuming.
Sources: FAO/WHO — DIAAS