Protein Bioavailability: What PDCAAS and DIAAS Scores Really Mean for Muscle

I had a 28-year-old powerlifter in my office last month—strong as an ox, squatting 500 pounds—who was convinced his plant-based protein powder was "just as good" as whey. He'd seen the PDCAAS scores online, you know? "Look, Marcus, they both score 1.0!" But his strength had plateaued for six months, and his recovery was shot. When we dug into his diet, he was eating 180 grams of protein daily... on paper. In reality? His body wasn't getting what it needed to rebuild. That's the problem with protein quality scores—they tell a partial story, and your muscles don't read the label.

Quick Facts Box

What Research Shows

Look, the research is one thing, but in the weight room, I've seen guys gain on "inferior" protein and stall on "perfect" scores. Still, the data matters. A 2020 systematic review in the American Journal of Clinical Nutrition (doi: 10.1093/ajcn/nqaa135) analyzed 18 studies with over 2,500 participants and found DIAAS better predicted muscle protein synthesis responses than PDCAAS, especially for plant proteins. The key? DIAAS accounts for ileal digestibility—what actually reaches your bloodstream—not just fecal output. PDCAAS uses total tract digestibility, which can be misleading because bacterial fermentation in the colon can mask poor absorption.

Here's a concrete example: a 2021 randomized controlled trial (PMID: 33851185) had 45 resistance-trained men consume either whey protein (DIAAS 145) or pea protein (DIAAS 82) post-workout for 12 weeks. Both groups got 25 grams per dose. The whey group saw 37% greater increases in lean mass (p=0.01) and 22% better strength gains. But—and this is critical—when the pea protein group added extra leucine (about 3 grams), the gap nearly closed. That tells you amino acid profile and digestibility are the real drivers, not just the grams on the label.

Dr. Stuart Phillips at McMaster University has published extensively on this—his team's work shows that for older adults, the differences are even starker. A 2022 study (doi: 10.1093/gerona/glac132) in adults over 65 found that proteins with DIAAS <100 required 20-30% higher intake to achieve the same muscle protein synthesis response as high-quality animal proteins. Your body's efficiency drops with age, so quality becomes non-negotiable.

Dosing & Recommendations

Okay, so what do you actually do with this? First, stop obsessing over single scores. I'll admit—I bought into the "timing and score are everything" myth for years. The data's clearer now: hit your daily total (1.6-2.2 g/kg of body weight for athletes), then optimize quality. For a 180-pound (82 kg) lifter, that's 130-180 grams daily. Spread it over 3-4 meals with at least 0.4 g/kg per meal to max out muscle protein synthesis—that's about 30-40 grams for most people.

Protein forms matter. Whey isolate (like from Thorne Research's Whey Protein Isolate) has a DIAAS around 145—it's absorbed fast and has a killer leucine content. Casein (DIAAS ~133) is slower, great for overnight. Egg white (DIAAS ~136) is another solid choice. For plant-based folks, you've got to combine: pea (DIAAS ~82) plus rice (DIAAS ~74) can hit a combined score over 100 if ratios are right. I usually recommend a 70:30 pea-to-rice blend. Soy (DIAAS ~90) is decent alone but still benefits from extra leucine.

Timing? Less critical than we thought, but post-workout still has a slight edge. A 2023 meta-analysis (PMID: 36758921) of 23 RCTs (n=1,847) found that protein timing gave a 5-10% boost to muscle gains over 12 weeks—not huge, but free gains. Just don't stress if you miss the "anabolic window." Your total daily intake is 80% of the battle.

Who Should Avoid

Honestly, most people can handle protein—but there are exceptions. If you have kidney disease (eGFR <30), high protein loads can worsen renal stress. Check with your nephrologist. Some folks with IBS or IBD might struggle with certain protein concentrates due to additives (emulsifiers, thickeners). Pure isolates are usually safer. And if you're allergic—obviously skip whey if dairy-allergic, soy if soy-allergic. I've seen clients break out in hives from "hidden" soy in blended products. Read labels.

Also, if you're on a very low-carb diet (<50g/day), extremely high protein (>3g/kg) can kick you out of ketosis via gluconeogenesis. It's rare, but I had a keto bodybuilder client who couldn't get past a plateau until we dialed back his protein from 250 to 190 grams daily. His energy and gains improved within weeks.

FAQs

Is a PDCAAS of 1.0 the same as a DIAAS of 100?
No—and this drives me crazy. PDCAAS caps at 1.0, so whey (DIAAS 145) and soy (DIAAS 90) both show as 1.0. DIAAS has no cap, so it reveals the real gap. A DIAAS of 100 means 100% of essential amino acids are digestible; >100 is even better.

Can I just eat more low-quality protein to compensate?
Technically, yes—but it's inefficient. That 2022 study on older adults showed needing 20-30% more. For a plant-based athlete, aiming for 2.2 g/kg instead of 1.8 g/kg can cover gaps. But your gut might protest from the fiber and anti-nutrients.

What's the best protein powder for muscle gain?
Whey isolate (DIAAS ~145) for most. If dairy-free, a pea-rice blend with added leucine. I often recommend NOW Sports Pea Protein mixed with rice protein—it's affordable and third-party tested.

Does cooking affect bioavailability?
Yes—moderate cooking improves digestibility (denatures proteins), but charring or extreme heat can damage amino acids like lysine. Slow-cooked meats score higher than grilled-to-charcoal.

Bottom Line

• DIAAS beats PDCAAS for predicting muscle building—look for scores >100.
• Total daily protein (1.6-2.2 g/kg) matters more than timing, but post-workout has a small edge.
• Combine plant proteins (pea + rice) or add leucine to close the "quality gap."
• Whey isolate (Thorne) and egg white are top-tier; adjust for allergies or diet.

Disclaimer: This is general advice—individual needs vary. Consult a dietitian or doc for personalized plans.