Reference
Muscle Protein Synthesis (MPS)
**Muscle Protein Synthesis (MPS)** is the metabolic process by which the body builds new skeletal muscle protein, incorporating dietary amino acids into muscle fibers. Net muscle growth occurs only when MPS exceeds Muscle Protein Breakdown (MPB) over time.
How MPS works
Muscle tissue is in constant flux, simultaneously building (synthesis) and degrading (breakdown). Hypertrophy requires MPS to exceed MPB across days and weeks, not a single meal (Phillips et al., 2014, Sports Medicine, PMID:24791918). Two non-genetic inputs drive the synthetic response: resistance exercise and protein intake.
At the molecular level, ingested amino acids — leucine in particular — signal through the mTOR pathway to initiate translation. Leucine is the primary amino acid trigger for MPS, which is why a protein’s leucine content, not just its total grams, matters. Plant proteins generally supply less leucine and produce a lower, slower rise in circulating essential amino acids than whey, which can make a given dose less effective per gram.
MPS and aging
The muscle’s synthetic response to protein is not fixed across the lifespan. With age, the same dose of protein produces a smaller increase in MPS — a condition termed anabolic resistance (Breen and Phillips, 2013, PMID:23558692). The synergistic effect of resistance exercise and protein ingestion is also delayed in older adults compared with the young (PMID:18323467). Anabolic resistance is a contributor to sarcopenia and a central reason older adults are advised to consume more protein per meal than younger ones. For athletes of every age, the practical implications are covered in our guide to protein for athletes.
Potato protein and MPS
Most direct human evidence on plant-protein anabolism uses whey, soy, or pea. Potato protein isolate is the exception with published clinical data. In a 2020 trial, consuming 25 g of potato protein isolate twice daily stimulated muscle protein synthesis rates in young women, both at rest and during recovery from resistance exercise (“Potato Protein Isolate Stimulates Muscle Protein Synthesis at Rest and with Resistance Exercise in Young Women,” Nutrients, 2020, PMID:32349353). Women who consumed the additional potato protein increased their rate of synthesis; the placebo group did not. The investigators characterized potato protein isolate as a high-quality plant-based protein capable of supporting an anabolic response — a notable finding given that plant proteins, in general, carry lower protein quality scores than animal proteins.
MPS is the mechanism that connects what is on the label to what happens in muscle. A protein with adequate leucine and good digestibility, eaten alongside resistance training, is what raises the synthetic rate above breakdown.
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