Amino acid profile (PDCAAS / DIAAS score)

Not all proteins are equal. The amino acid profile rates the quality of a protein source on two criteria: its essential amino acid composition (does it contain all 9 in good proportions?) and its digestibility (does the body absorb them well?).

Two official scores:

• PDCAAS (the older standard, capped at 1.0)
• DIAAS (the newer, more precise standard, which measures actual ileal absorption)

A fresh angle (beyond the complete/incomplete binary): these scores add nuance to the simplistic “complete versus incomplete protein” debate. They show that quality is a spectrum, not a binary category:

• Egg, milk, whey: among the highest scores (the reference), perfect profile and high digestibility
• Meat, fish: excellent
• Soya: very good (the best-rated plant source, almost equal to animal sources)
• Pulses: good but limited in methionine
• Cereals: limited in lysine

The concept of the limiting amino acid: the score depends on the weakest link. The essential amino acid present in the lowest proportion “caps” how well the whole protein is used. A cereal on its own (low in lysine) has a low score, but combined with a pulse (rich in lysine), the pair reaches a complete profile. This is the famous complementarity (rice + lentils, hummus + bread).

The limits of the scores: these measures have their critics:

1. They assess a protein in isolation, not a whole meal (where sources complement each other)
2. They do not capture all the benefits of a food (fibre, micronutrients in pulses that whey lacks)
3. The combination across the day matters more than the score of each food taken alone

Practical implication: for an omnivore, protein quality is never a problem. For a vegan, varying sources (pulses + cereals + soya + nuts and seeds) across the day ensures a complete amino acid profile. There is no need to combine at every meal (the body’s amino acid pool “smooths things out” over 24 hours).