posted on 2023-07-26, 16:15authored byFJ Dijk, Z Hofman, YC Luiking, MJW Furber, JD Roberts, A van Helvoort, M van Dijk
P4, a specific combination of dairy proteins (whey and casein) and plant‐based protein
isolates (pea and soy), has been shown to provide a more balanced amino acid (AA) profile than its
single constituent proteins; however, less is known about how this translates to muscle protein syn‐
thesis (MPS). The aim of this study was to investigate the effect of P4 compared to whey or casein
against fasted control on MPS. C57BL/6J mice, aged 25 months, were fasted overnight, followed by
oral gavage of either whey, P4, casein, or water as a fasted control. Thirty minutes after ingestion,
puromycin (0.04 μmol∙g‐1 bodyweight) was subcutaneously injected; 30‐min thereafter, mice were
sacrificed. MPS was measured by the SUnSET method, and signalling proteins were determined in
the left‐tibialis anterior (TA) muscle by the WES technique. AA composition was determined in
plasma and right‐TA muscle. Dried blood spots (DBS) were analysed for postprandial AA dynamics
at 10, 20, 45, 60 min. MPS was 1.6‐fold increased with whey (p = 0.006) and 1.5‐fold with P4 com‐
pared to fasted (p = 0.008), while no change was seen with casein. This was confirmed by a signifi‐
cant increase of phosphorylated/total ratio of 4E‐BP1 for both whey (p = 0.012) and P4 (p = 0.001).
No changes were observed in p70S6K and mTOR phosphorylation/total ratio with whey or P4. In‐
tramuscular leucine levels were lower for P4 (0.71 μmol∙g dry weight−1) compared to whey (0.97
μmol∙g dry weight−1) (p = 0.0007). Ten minutes postprandial, DBS showed significantly increased
blood AA levels of BCAAs, histidine, lysine, threonine, arginine, and tyrosine for P4 versus fasted.
In conclusion, a hybrid mix of dairy and plant‐based proteins (P4) resulted in a MPS response that
was similar to whey protein in aged mice after fasting. This suggests that other anabolic triggers
beyond leucine or the well‐balanced amino acid profile and bioavailability of the blend benefit stim‐
ulation of MPS.