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nutrition 3 min read

PDCAAS and DIAAS: The Science Behind Protein Quality

Not all protein is created equal. Here's what PDCAAS and DIAAS actually measure — and what they mean for your food choices.

PDCAAS and DIAAS: The Science Behind Protein Quality

Grams of Protein Aren't the Whole Story

You already know you need protein. You probably already track how many grams you eat per day. But here's what most people don't know: not all grams of protein are equal. A 30g protein serving from chicken breast and a 30g protein serving from wheat flour are very different things — and two scoring systems, PDCAAS and DIAAS, exist to measure exactly that difference.

What Is PDCAAS?

PDCAAS stands for Protein Digestibility-Corrected Amino Acid Score. It was adopted by the World Health Organization (WHO) in 1993 as the gold standard for measuring protein quality.

It works by evaluating two things:

  1. Amino acid profile — does the protein contain all nine essential amino acids in adequate amounts relative to human requirements?
  2. Digestibility — what percentage of the protein is actually absorbed and used by the body?

The score is expressed as a number from 0 to 1 (or 0–100%). A score of 1.0 is the maximum. Foods like whey protein, eggs, and beef all score 1.0. Many plant proteins score significantly lower because they're either missing or low in one or more essential amino acids.

What Is DIAAS?

DIAAS stands for Digestible Indispensable Amino Acid Score. It's the newer, more precise system introduced by the FAO in 2013 to address limitations in PDCAAS.

The key difference: DIAAS measures amino acid digestibility in the small intestine specifically, rather than overall digestibility. This is more accurate because the small intestine is where amino acids are actually absorbed into the bloodstream. PDCAAS was based on fecal digestibility — which is less precise.

DIAAS can exceed 1.0 (meaning the protein actually exceeds human requirements for all essential amino acids). Milk protein, for example, scores around 1.18.

Why Does This Matter For You?

If you're eating primarily plant-based protein sources, PDCAAS and DIAAS become critical. Many plant proteins — like wheat, rice, or hemp — are low in one or more essential amino acids (typically lysine or methionine). That means even if you're hitting your gram target, you may not be getting full benefit.

The solution? Protein complementation — combining plant sources to cover each other's amino acid gaps. Rice + beans, for example, creates a complementary amino acid profile that together approaches a complete protein score.

Animal proteins (meat, eggs, dairy, fish) and soy are considered complete proteins — they score 1.0 or higher on PDCAAS/DIAAS and contain all essential amino acids in sufficient quantities.

Practical Takeaway

When you're planning your meals, don't just count grams — consider quality. If your protein sources are primarily animal-based or include complete plant proteins like soy or quinoa, you're likely fine. If you rely heavily on grains or legumes, make sure you're pairing them thoughtfully and potentially eating more total protein to compensate for lower digestibility scores.

Our Protein Quality Score tool in the app applies these scores automatically so you can see exactly how your protein sources stack up — without needing a biochemistry degree.