The Stubborn Myth of 'Incomplete Protein'
Frances Moore Lappé's 1971 bestseller Diet for a Small Planet popularized 'protein combining' — the idea that plant proteins are incomplete and must be paired at every meal. Lappé herself retracted that claim in later editions, but the myth has outlived her revisions by half a century.
In 1994, Vincent Young and Peter Pellett at MIT delivered the decisive blow in American Journal of Clinical Nutrition. Humans maintain an 'amino acid pool' in liver and gut; all essential amino acids do not need to coincide within a single meal. Eat varied plant foods across the day and the pool fills. The WHO/FAO/UNU 2007 joint report and the Academy of Nutrition and Dietetics' 2016 position both concluded the same: 'Well-planned vegan diets are appropriate for all life stages.'
DIAAS — The Real Scorecard for Plant Protein
The old standard was PDCAAS (Protein Digestibility-Corrected Amino Acid Score), but it was capped at 1.0, producing the absurd result that soy and milk both scored '1.0.' In 2013 FAO replaced it with DIAAS (Digestible Indispensable Amino Acid Score), which measures true ileal absorption and allows scores above 1.0.
From Mathai 2017 and Phillips 2017:
- Soy isolate: 0.91–1.0 — highest among plants
- Pea isolate: 0.82 — rich in lysine
- Oats: 0.67
- Brown rice: 0.59 — limited in lysine
- Legumes (lentils, black beans, chickpeas): 0.50–0.65 — limited in methionine
- Wheat (gluten/seitan): 0.45 — lysine-deficient
For context: milk 1.18, egg 1.13, beef 1.10. Soy is 5% below milk, not half.
Lower-scoring foods recover their score in 'complementary pairs.' Legumes (low methionine) + grains (low lysine) cover each other. Mexican beans + rice, Middle Eastern hummus (chickpeas + sesame), Indian dal + roti, East Asian tofu + rice — humans have followed DIAAS without knowing it for millennia.
A Scorecard for Vegan Protein Foods
| Food | Protein (100g) | DIAAS | Per-meal example |
|---|---|---|---|
| Firm tofu | 8 g | 0.52 | 150 g serving ≈ 12 g |
| Tempeh | 18–20 g | 0.67 | 100 g steak ≈ 19 g |
| Edamame | 11 g | 0.91 | 1 cup ≈ 17 g |
| Lentils (cooked) | 9 g | 0.52 | 200 g curry ≈ 18 g |
| Chickpeas (cooked) | 9 g | 0.65 | 4 tbsp hummus ≈ 8 g |
| Black beans (cooked) | 9 g | 0.59 | Bean rice add-on ≈ 8 g |
| Quinoa | 4.4 g | 0.85 | 1 bowl salad ≈ 8 g |
| Pea isolate | 80–85 g | 0.82 | 1 scoop 30 g ≈ 24 g |
| Seitan (wheat) | 25 g | 0.45 | 100 g ≈ 25 g (pair with soy) |
| Hemp seeds | 33 g | 0.66 | 30 g ≈ 10 g |
| Chia seeds | 17 g | 0.40 | 30 g ≈ 5 g |
Vegans Build Muscle Too — Hevia-Larraín 2021 RCT
The 'vegans can't build muscle' folklore collapsed in Sports Medicine in 2021. Hevia-Larraín's team at the University of São Paulo randomized 38 resistance-trained men into ① omnivorous + soy supplement and ② vegan + soy supplement for 12 weeks. Both groups took 1.6 g/kg/day protein and followed identical training.
Result: quadriceps cross-section, strength, hypertrophy — no significant difference between groups. With enough total intake and proper distribution, plant-only diets matched omnivorous diets for muscle growth in trained men — the first RCT to show it.
Van Vliet 2015's review noted that whey beats soy on a per-dose basis for muscle protein synthesis (MPS), but Pinckaers' 2024 meta-analysis concluded that 'proper plant blends (soy + pea, pea + rice) match animal protein at adequate doses.' The key is meeting the 20–40 g per dose with ≥2.5–3 g leucine threshold. Animal vs plant matters less than 'did you eat enough?'
Supplements — When and What
Vegan protein powder is convenience, not necessity. If whole foods cover 1.2–1.6 g/kg/day, no powder needed. Useful when:
- Athletes needing >1.6 g/kg — whole foods alone push calories too high
- Elderly with anabolic resistance — concentrated per-meal dose
- Surgery/trauma recovery
- Busy commuters with frequent eating out
Options:
- Soy protein isolate: 90% protein, DIAAS near 1.0, best value.
- Pea isolate: rich in lysine, arginine, BCAAs, low allergenicity.
- Pea + rice blend: methionine (rice) and lysine (pea) complement — closest to whey.
- Hemp protein: lower concentration (50%) but bundles omega-3.
- Avoid: 'protein drinks' with >20 g added sugar — dessert, not recovery.
Korean Cuisine — Already Set Up
Korea has one of the world's richest vegan protein food cultures. The protein spine of traditional Korean food was soy, not meat.
- Tofu, soft tofu, sundubu: easiest way to add 12–20 g per meal.
- Cheonggukjang, natto: fermented soy, K2 plus live cultures. Fermentation improves absorption.
- Doenjang, soy sauce: fermented soy seasoning, flavor plus trace protein and isoflavones.
- Soybean sprouts, kongbiji: budget protein peaks; a bowl of soybean-sprout rice soup ≈ 10 g.
- Meju, traditional doenjang: not DIAAS-measured but amino acids more bioavailable via fermentation.
- Temple cuisine: 1700-year vegan tradition — sophisticated tofu, soy, perilla, pine nut, walnut combinations.
- Plant-based processed: Pulmuone 'Earth Diet,' Jayeon Chae plant dumplings, LG plant-based drinks — booming since 2020s. Highly processed, so cap at one serving daily.
'Vegan = only salads' is the biggest misconception. Brown rice + cheonggukjang + braised tofu + soybean-sprout soup + a handful of nuts clears 30 g of protein in a single Korean meal.
Special Populations
Children: Lee Eun-young (2019) review for the Korean Pediatric Society concluded well-planned vegan diets work for infants and children, but B12, iron, zinc, omega-3, vitamin D need monitoring. Parental nutrition literacy is the key variable.
Pregnancy/lactation: protein needs rise to 1.1 g/kg/day plus 25 g/day in late pregnancy. B12 deficiency can cause irreversible neonatal neurological damage — supplement is non-negotiable.
Elderly: anabolic resistance raises the leucine threshold. Target ≥1.0–1.2 g/kg/day with 25–30 g protein per meal; soy isolate or pea+rice blends are practical.
Athletes: total intake (1.6–2.2 g/kg/day) is the lever. Vegan athletes who meet it perform equivalently (Hevia-Larraín 2021). Whole-food-only diets may overshoot calories — sensible powder use.
Conclusion: Not Completeness, but Total and Distribution
Fifty years of the plant-protein debate distill to one line. Not 'completeness in one meal' but 'total across the day and distribution across four meals.' Young & Pellett 1994, FAO DIAAS 2013, and Hevia-Larraín 2021 all point the same way — plant protein is sufficient; you just need enough of it.
Look again at tonight's tofu cube, bowl of cheonggukjang, and rice with beans. That's not a deficiency risk — it's a 1700-year-refined Korean DIAAS prescription.
