Why Complete Protein Changes Everything

What Is a Complete Protein?

A protein is considered complete when it contains all nine essential amino acids (EAAs) in adequate quantities. These are amino acids the human body cannot synthesise on its own and must obtain from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

The distinction matters more than most nutritional labels suggest. You can consume large quantities of protein — meeting your daily gram target — and still be limiting your muscle protein synthesis if the source is missing or low in one or more EAAs. The body cannot complete the synthesis of a new protein molecule if even one required amino acid is absent. This is sometimes called the limiting amino acid concept.

The Scoring Systems: PDCAAS vs DIAAS

For decades, protein quality was measured using the Protein Digestibility Corrected Amino Acid Score (PDCAAS). It compares a protein's amino acid profile against the human requirement pattern and adjusts for digestibility. A score of 1.0 is the theoretical maximum.

However, PDCAAS has known limitations — it caps at 1.0 regardless of actual amino acid surplus, and its digestibility measure is fecal rather than ileal, meaning it overestimates how much protein is actually absorbed before reaching the large intestine.

The FAO now recommends the Digestible Indispensable Amino Acid Score (DIAAS), which uses true ileal digestibility data and doesn't cap scores at 1.0. Under DIAAS, animal proteins consistently score higher — and notably, cricket protein scores comparably to casein and above most plant proteins.

Leucine: The Trigger

Of all the essential amino acids, leucine occupies a unique position. It is not merely a building block — it is a signalling molecule that directly activates the mTOR (mechanistic target of rapamycin) pathway, the master regulator of muscle protein synthesis.

Research by Norton & Layman (2006) established that a minimum leucine dose of approximately 2–3g per meal is required to maximally stimulate MPS. Below this threshold, the anabolic signal is attenuated even if total protein intake is adequate. This is why leucine-rich, complete protein sources — eggs, dairy, meat, and cricket — generate superior anabolic responses compared to leucine-poor plant proteins consumed at the same gram-for-gram dose.

Practical Implications

If you consume 30g of pea protein, you are not getting the same anabolic stimulus as 30g of cricket or whey protein. The leucine content of pea protein (~6.4% of protein) is significantly lower than cricket (~9.1%) or whey (~10.9%). To match the leucine dose from 30g of whey, you would need approximately 50g of pea protein — a 67% greater dose, with proportionally more calories.

• Choose complete proteins first.Every meal is an opportunity for a maximal anabolic signal — don't waste it on incomplete sources when complete options are available.
• Count leucine, not just grams.A protein source with 65g/100g content and high leucine fraction (like cricket) delivers more per serving than a plant source at equivalent dose.
• Combination strategies work.Pairing incomplete plant proteins (e.g. rice + pea) can approximate completeness — but still underperforms complete animal sources on leucine per gram.