DIAAS Protein Scores: The Rating System That Reveals the Truth About Protein Quality

Two protein powders sit on the shelf. Both say "30g protein." Same price. Same size. But one will help you build muscle, and the other won't. The difference? DIAAS scores - and most people have never heard of them.

What is DIAAS?

DIAAS stands for Digestible Indispensable Amino Acid Score.

It's the new gold standard for measuring protein quality, recommended by the FDA and FAO (Food and Agriculture Organization) since 2013.

DIAAS tells you one critical thing: How much of the protein you eat can your body actually digest and use?

Why We Needed a New System

For decades, we used a system called PDCAAS (Protein Digestibility Corrected Amino Acid Score).

PDCAAS had two major flaws:

DIAAS fixes both problems.

How DIAAS Works

DIAAS measures protein digestibility at the end of the ileum - the last part of your small intestine where amino acid absorption happens.

This gives a much more accurate picture of what your body actually absorbed and can use.

And DIAAS doesn't cap scores at 100%. Scores can go above 1.0 if a protein is exceptionally high quality.

The DIAAS Scorecard

HIGH QUALITY (DIAAS > 1.0)

Your body absorbs and uses MORE than 100% of the protein:

Protein Source	DIAAS Score
Whole milk powder	1.14
Whole eggs	1.13
Beef	1.11
Whey protein isolate	1.09
Chicken breast	1.08

What this means: These are premium proteins. Your body absorbs essentially all of them, plus they provide amino acids in optimal ratios.

MODERATE QUALITY (DIAAS 0.75-1.0)

Your body absorbs 75-90% of the protein:

Protein Source	DIAAS Score
Soy protein isolate	0.90
Pea protein concentrate	0.82

What this means: Decent proteins, but your body loses 10-25% of what you eat. You need to eat MORE to get the same usable protein as high-DIAAS sources.

LOW QUALITY (DIAAS < 0.75)

Your body absorbs less than 75% of the protein:

Protein Source	DIAAS Score
Rice protein concentrate	0.59
Cooked black beans	0.54
Wheat protein	0.40

What this means: Your body struggles to use these proteins efficiently. With wheat protein at 0.40, your body only uses 40% of what you eat. The other 60% is wasted.

The Shocking Drop When Switching to DIAAS

When scientists re-tested proteins with the more accurate DIAAS system, some proteins' scores CRASHED:

• Wheat protein: Was 1.0 (perfect) under PDCAAS → Dropped to 0.40 under DIAAS
• Soy protein: Was 0.98 → Dropped to 0.90
• Pea protein: Was 0.93 → Dropped to 0.82

Meanwhile, animal proteins went UP or stayed high:

• Whey protein: Was 1.0 → Rose to 1.09
• Milk protein: Was 1.0 → Rose to 1.14
• Eggs: Stayed high at 1.13

The more accurate the measurement, the bigger the gap between animal and plant protein quality.

Real-World Example: Two Protein Powders

Let's compare two protein powders, both claiming "30g protein per serving":

Same label claim. 175% difference in what your body actually gets.

This is why two people can follow the same "100g protein per day" plan and get completely different results.

The SOURCE of protein matters as much as - or MORE than - the total grams.

Practical Takeaways for Women Over 40

1. Choose High-DIAAS Proteins When Possible

For muscle preservation, prioritize proteins with DIAAS > 1.0:

• Whey protein
• Eggs
• Dairy (milk, Greek yogurt, cottage cheese)
• Chicken, beef, fish

2. If Plant-Based, Eat 25% More Protein

Since plant proteins have lower DIAAS scores (0.54-0.90), you need more total protein to get the same usable amount.

If your goal is 100g protein from animal sources, aim for 125g from plant sources.

3. Check Your Protein Powder

Read the ingredient list, not just the protein grams:

• Whey isolate or concentrate: Excellent (DIAAS 1.09)
• Egg white protein: Excellent (DIAAS 1.13)
• Casein: Excellent (DIAAS ~1.1)
• Soy isolate: Good (DIAAS 0.90)
• Pea protein: Moderate (DIAAS 0.82)
• Rice or wheat protein: Poor (DIAAS 0.40-0.59)

4. Combine Plant Proteins Strategically

Mixing complementary plant proteins (like pea + rice) can boost the overall DIAAS score by providing a better amino acid profile.

Look for plant protein blends rather than single-source plant proteins.

Why Doesn't Every Label Show DIAAS?

Great question.

DIAAS scores reveal that cheap plant proteins (rice, wheat, pea) are nowhere near as effective as whey or egg proteins.

Manufacturers of plant-based protein powders aren't eager to advertise that their product has a DIAAS of 0.59 when whey protein has a DIAAS of 1.09.

But as an informed consumer, you can look up DIAAS scores for common protein sources and make better choices.

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Sources: British Journal of Nutrition 2017; FAO 2013; Journal of Nutrition 2018