When it comes to protein, the standard advice often boils down to hitting your daily Recommended Dietary Intake (RDI)—typically around 0.8g per kilogram of body weight. But here's the catch: the RDI is based largely on nitrogen content, not on how effectively different proteins support muscle retention, recovery, or growth. In reality, not all proteins are created equal—and that matters, especially if your goal is preserving or building lean muscle mass.
One of the biggest differentiators in protein quality is bioavailability—how well your body can digest, absorb, and use the amino acids in a protein source. Animal proteins like whey, eggs, and meat generally have high bioavailability, meaning more of the protein you consume actually gets used by your muscles. Plant proteins, on the other hand, tend to be less bioavailable due to fibre, anti-nutrients, and incomplete amino acid profiles.
But beyond bioavailability, the amino acid profile of your protein is critical—particularly when it comes to leucine.
Leucine is a branched-chain amino acid (BCAA) that plays a central role in triggering muscle protein synthesis (MPS). Research suggests that a minimum of 2.5g of leucine per meal is needed to optimally stimulate MPS in most people. And this is where things get interesting.
Let’s compare: 25g of whey protein isolate contains about 3g of leucine. That’s a single scoop—quick, efficient and <100 calories. By contrast, to get the same amount of leucine from quinoa, you'd need to consume over 700 calories’ worth, or about 6 cups cooked. With lentils, it’s about 3.5 cups—over 650 calories. Even soy, one of the better plant-based options, still requires over 35g of protein and 300+ calories to hit the leucine threshold.
That means someone trying to rely on lower-leucine plant proteins may need to consume twice the protein and nearly triple the calories to match the muscle-stimulating power of a smaller serving of a high-leucine, high-bioavailability animal protein.
This doesn’t mean plant proteins are useless—but if you're focused on muscle retention, body composition, or athletic performance, protein quality—not just quantity—should guide your choices. Especially as you age or train harder, meeting that leucine threshold per meal can be the difference between maintaining lean mass and slowly losing it.
So, next time you think about protein, go beyond the grams. Think bioavailability, amino acids, and especially leucine—because when it comes to building muscle, quality trumps quantity every time.
