What is Muscle Protein Synthesis?
Short for MPS
The process of building new muscle tissue. Driven by protein intake and resistance training.
Muscle protein synthesis (MPS) is the process of building new muscle proteins from amino acids — the cellular machinery that translates the protein you eat into actual muscle tissue. It runs continuously, balanced against muscle protein breakdown (MPB). Net muscle gain happens when MPS exceeds MPB sustained over time.
Quick definition
Eat protein, MPS spikes. Lift heavy, MPS spikes higher. Do both, MPS spikes highest. The honest building of new muscle is a long string of protein-driven MPS spikes plus training stimulus.
How it actually works
MPS responds to two main triggers: dietary protein (specifically the essential amino acid leucine) and mechanical loading from resistance training. The leucine threshold for triggering meaningful MPS is roughly 2 to 3 grams per meal — about what's in 25 to 40 grams of complete protein from chicken, fish, eggs, dairy, or whey.
The 2017 ISSN position stand (Jäger et al.) and a decade of work from Stuart Phillips's lab at McMaster show MPS plateaus around 0.3 to 0.4 g of protein per kg bodyweight per meal — so 25 to 40 g per meal, three to four meals per day, is the practical target. More protein per sitting doesn't add MPS; it gets oxidized.
Resistance training elevates MPS for 24 to 48 hours post-workout. That's why the timing of post-workout protein matters less than people think — you have a 24+ hour window, not a 30-minute one. The "anabolic window" panic is mostly retired by the research community.
Why it matters for weight loss
If you're trying to preserve lean body mass on a cut, MPS is the gate you have to keep open. Three to four 30-to-40g protein meals per day, two to four resistance training sessions per week. That's the recipe. Anything fancier is detail.
Common misconceptions
The biggest myth: protein has to be from animal sources. Plant proteins (soy, pea, complete blends) trigger MPS effectively if total leucine content is matched. The dose required is slightly higher with plant-only — 40g instead of 30g per meal.
The second myth: you need the gym to keep MPS elevated. Even bodyweight resistance work (push-ups, squats, planks, bands) is enough to maintain MPS in the absence of equipment. Frequency matters more than tonnage at the maintenance level.
Related terms
- Lean Body Mass Everything you weigh that isn't fat — muscle, bone, organs, water. What you protect during a diet.
- Sarcopenia Age-related muscle loss. Starts around 30, accelerates after 60. The reason resistance training matters more with age.
- Thermic Effect of Food · TEF The 10% or so of calories your body burns just digesting what you ate.
- Calorie Surplus Eating more calories than you burn — the mechanism behind weight gain (and muscle gain).
- BMR · Basal Metabolic Rate The calories your body burns at complete rest just to keep you alive.
Read next on Real Easy Diet
Sources
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[01]
Protein for older adults — Harvard Health Harvard Health
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[02]
ISSN protein position stand NIH PMC
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