Paper 001 · 2023

The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans

Jorn Trommelen, Glenn A.A. van Lieshout, Jean Nyakayiru, Andrew M. Holwerda, Joey S.J. Smeets, Floris K. Hendriks, et al. · Cell Reports Medicine 4, 101324

A big post-workout protein meal (100 g) builds more muscle, for longer than 12 hours, than the usual 25 g — the old 'cap it at 25 g' rule is wrong.In trained males, 100 g whey post-leg-day raised muscle protein synthesis higher and for >12 h vs 25 g, with little extra oxidation — the per-meal cap is an artefact of short measurement windows.Trommelen et al. used L-[1-13C]-phenylalanine and L-[ring-2H5]-phenylalanine tracers to show dose-dependent, non-saturating MPS (mixed, myofibrillar, connective, plasma) over a 12-h post-prandial window after 25 vs 100 g intrinsically labelled milk protein, with negligible AA oxidation surplus.

strengthendurancenutritionrecoveryphysiology

TL;DR

You can absorb and use a lot more protein per meal than the textbook says. Trommelen and colleagues fed athletes either 25 g or 100 g of milk protein after a leg workout and tracked, with isotope tracers, where every amino acid went. The 100 g dose drove muscle protein synthesis higher and for longer than 12 hours — roughly twice as much net protein laid down. Excess amino acids were not just burned off. The “no point eating more than 20–25 g in one sitting” rule looks like an artefact of studies that didn’t watch long enough.

Key findings

  • 1

    100 g protein → bigger and longer anabolic response than 25 g

    Both magnitude and duration of muscle protein synthesis (MPS) were dose-dependent — no plateau in the studied range.

  • 2

    MPS stayed elevated for >12 hours after the 100 g meal

    Earlier 'plateau' studies stopped measuring at 4–6 h, missing the long tail.

  • 3

    Whole-body protein breakdown barely changed with dose

    The dose effect comes from synthesis, not from suppressing breakdown.

  • 4

    Only a small fraction of extra amino acids was oxidised

    Contradicts the assumption that excess protein is just burned for energy.

  • 5

    Effects covered mixed-muscle, myofibrillar, connective and plasma protein

    So both contractile tissue and connective/recovery tissue benefit.

What this means for your training

  • For most athletes, you don’t need to obsess over splitting protein into 4×25 g meals. A bigger post-session feed (40–60 g+ if your appetite allows) is almost certainly not “wasted.”
  • Travel days, fasted training, or one-big-meal eating patterns are less catastrophic than the 25 g dogma suggests. The body keeps using amino acids for hours after a large bolus.
  • For older athletes and those with reduced muscle-building sensitivity, this study is one more piece of evidence that higher per-meal protein doses are usable.
  • It does not say “more is always better.” The benefit-per-gram still tapers off; 4×25 g vs. 1×100 g across the day is yet to be tested head-to-head for long-term muscle growth. Total daily protein (~1.6–2.2 g/kg for trained athletes) remains the primary lever.

Try it yourself

Slide the protein dose and watch the synthesis curve. Notice how going from 25 g to 100 g doesn’t just lift the peak — it stretches the tail far past the window most older studies stopped measuring.

Anabolic response simulator

Stylised — for intuition
baseline0h2h4h6h8h10h12h14hHours after ingestionMPS rate (%/h)
Peak rate
0.068 %/h
Duration above baseline
~4.0 h
Net synthesis (AUC)
0.14 arb.

Slide between 25 g and 100 g and notice that the curve doesn't just get taller — it gets longer. That stretched tail is the paper's central finding.

Methodology — plain language

Twelve healthy resistance-trained young men did a single bout of leg-resistance exercise, then drank either 0 g, 25 g or 100 g of intrinsically-labeled milk protein. “Intrinsically labeled” means the cows that produced the milk were fed labeled amino acids, so the researchers could trace exactly which amino acids in the bloodstream and muscle came from the drink versus the body’s own stores.

They used a quadruple isotope tracer infusion plus repeated muscle biopsies over 12 hours to measure:

  1. How fast amino acids appeared in the blood (digestion + absorption rate)
  2. How fast they were incorporated into different muscle proteins (synthesis)
  3. How much protein the body broke down (breakdown)
  4. How much was burned for energy (oxidation)

The clever bit is the long observation window. Earlier studies cut off at 4–6 h and so couldn’t see the extended tail of the 100 g response.

Methodology — detail

  • Design: Randomised, parallel-group; 36 healthy resistance-trained males (12 per arm), fasted overnight, performed a single bout of one-legged resistance exercise, then ingested 0, 25, or 100 g of intrinsically L-[1-¹³C]- phenylalanine and L-[1-¹³C]-leucine labeled milk protein concentrate (MPC).
  • Tracer approach: Continuous primed-constant infusions of L-[ring-²H₅]- phenylalanine, L-[3,5-²H₂]-tyrosine, and L-[1-¹³C]-leucine combined with the intrinsically labeled meal. Two MPC batches with different enrichments were produced and mixed (67:33) to hit target enrichments of 31.6 MPE phenylalanine and 8.0 MPE leucine.
  • Sampling: Arterialised-venous blood draws + serial muscle biopsies over the 12-hour postprandial period; expired-breath ¹³CO₂ for oxidation rates.
  • Outcomes: Mixed-muscle, myofibrillar, muscle connective, and plasma protein synthesis rates (FSR via incorporation of labeled phenylalanine); whole-body protein synthesis, breakdown, oxidation, and net balance via the endogenous Phe/Tyr model.
  • Key statistical claim: Linear/dose-response relationship across the 0/25/100 g arms for synthesis magnitude and duration, with no plateau. Whole- body breakdown and oxidation showed only minor dose dependence.
  • Limitations: Acute single-meal study in young trained males; does not directly test chronic muscle growth or distribution-pattern effects; protein source was a single milk-protein matrix.

How this fits into the literature

The dominant model — based on Moore (2009), Witard (2014), Macnaughton (2016) — held that ~20–25 g (or ~0.4 g/kg) maximises after a workout muscle-building rate and that further intake is oxidised. Those studies stopped at 4–6 h. The Trommelen 2023 result suggests the apparent plateau was partly a measurement-window artifact: the larger dose continues driving net positive balance well beyond when older protocols stopped sampling. Practical implication: per-meal recommendations should be re-examined with longer after eating windows, and the assumption that distribution dominates over total intake deserves a re-test.

Citation

Cite: Jorn Trommelen, Glenn A.A. van Lieshout, Jean Nyakayiru, Andrew M. Holwerda, Joey S.J. Smeets, Floris K. Hendriks, et al. (2023). The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Reports Medicine 4, 101324. https://doi.org/10.1016/j.xcrm.2023.101324

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