Beyond "Eat Protein, Build Muscle"
Everyone knows protein builds muscle. But how exactly does this work? What happens at the cellular level when you train and eat? Understanding muscle protein synthesis (MPS) helps you optimize training and nutrition decisions.
What Is Muscle Protein Synthesis?
Muscle protein synthesis is the process by which your body creates new muscle proteins. Your muscles are constantly in flux, with proteins being built (synthesis) and broken down (breakdown) simultaneously.
Think of it like a brick wall under constant renovation. Workers are always adding new bricks while weather erodes existing ones. If brick-laying exceeds erosion, the wall grows. If erosion wins, the wall shrinks.
For muscle growth, MPS must exceed muscle protein breakdown (MPB) over time. This net positive balance is called "net protein balance" and is the fundamental requirement for hypertrophy.
How Training Triggers MPS
Resistance training is the primary stimulus for MPS. When you lift weights:
- Mechanical tension signals muscle fibers that they need to adapt
- This activates the mTOR pathway, the master regulator of muscle protein synthesis
- MPS rates increase dramatically, peaking around 24 hours post-workout
- Elevated MPS can persist for 24-72 hours, depending on training status
Here's a crucial insight from research: in trained individuals, MPS returns to baseline faster (around 24-48 hours) compared to beginners (up to 72 hours). This supports why training each muscle multiple times per week may be optimal for experienced lifters.
The Role of Protein
Training alone isn't enough. You need amino acids (from dietary protein) to actually build new muscle tissue. Protein consumption after training enhances and extends the MPS response.
Key findings on protein and MPS:
- 20-40g of protein per meal maximizes MPS in most people
- Larger individuals and whole-body training may benefit from the higher end (40g)
- Leucine is the amino acid that most powerfully triggers MPS
- You need approximately 2-3g of leucine per meal to maximize the MPS signal
The Leucine Trigger
Leucine is special among amino acids. It directly activates mTOR, the enzyme that initiates protein synthesis. This is why leucine content matters as much as total protein.
Leucine content of common proteins (per 25g protein):
- Whey protein: ~3g leucine
- Eggs: ~2.2g leucine
- Chicken breast: ~2.1g leucine
- Beef: ~2.0g leucine
- Plant proteins (pea, rice): ~1.5-1.8g leucine
This explains why animal proteins typically produce stronger MPS responses than plant proteins at equal doses. Plant-based eaters can compensate by consuming more total protein or supplementing with leucine.
Protein Distribution Matters
Research shows that distributing protein intake across multiple meals is superior to consuming it in one or two large doses:
Suboptimal: 10g breakfast, 20g lunch, 70g dinner
Optimal: 30-40g at each of 3-4 meals
Each protein-rich meal triggers an MPS response that lasts several hours. By spacing meals, you can stimulate MPS multiple times per day rather than once.
The Muscle Full Effect
There's a ceiling to how much MPS can be stimulated per meal. Research shows that after approximately 20-40g of protein, additional protein doesn't further increase MPS. This is called the "muscle full" effect.
The excess protein isn't wasted: it's oxidized for energy or used elsewhere. But for the specific goal of maximizing muscle growth, there's no benefit to mega-dosing protein at single meals.
Training and Protein: The Synergy
Training and protein work synergistically. Neither is fully effective alone:
- Training without protein: MPS increases but lacks building blocks, limiting growth
- Protein without training: MPS increases modestly but without the training signal, growth is minimal
- Training + protein: MPS is maximized, and the response is amplified for 24-48 hours
This synergy is why post-workout protein matters. Training "sensitizes" muscles to protein, making subsequent meals more anabolic.
Practical Applications
Based on MPS research, here's how to optimize muscle growth:
1. Eat protein at every meal: Aim for 30-40g of high-quality protein 3-4 times daily.
2. Prioritize leucine-rich sources: Dairy, eggs, meat, and fish are optimal. Vegetarians should eat larger portions or supplement.
3. Train frequently: Since MPS elevations are transient (24-48 hours in trained individuals), hitting each muscle 2-3x weekly keeps the growth signal active.
4. Consume protein around training: A protein-rich meal within a few hours of training takes advantage of enhanced muscle sensitivity.
5. Don't skip breakfast: After an overnight fast, your muscles are primed for protein. A protein-rich breakfast triggers the first MPS spike of the day.
The Bottom Line
Muscle growth isn't magic. It's a biological process driven by muscle protein synthesis exceeding breakdown. Training triggers MPS; protein provides the raw materials. By understanding this process, you can make informed decisions about meal timing, protein distribution, and training frequency.
The science is clear: train hard, eat enough protein (1.6-2.2g/kg daily), distribute it across meals, and prioritize leucine-rich sources. Do this consistently, and muscle growth is inevitable.
Reference
McGlory C, Devries MC, Phillips SM. Skeletal muscle and resistance exercise training; the role of protein synthesis in recovery and remodeling. J Appl Physiol. 2017;122(3):541-548. PMID: 25739559