So I skimmed through the paper, and here’s some interesting takeaways from it.
Relative to untrained participants, resistance-trained participants have a smaller potential for muscle growth72 and an attenuated postexercise muscle protein turnover.73 As a result, we speculate that trained persons may have less ‘degrees of freedom’ to change with RET and therefore have a greater need for protein supplementation to see increases in muscle mass.
Older individuals are anabolically resistant74 and require higher per-meal protein doses to achieve similar rates of MPS, the primary variable regulating changes in skeletal muscle mass,75 compared with younger participants.
A recent retrospective analysis showed a ‘breakpoint’ for the stimulation of MPS when ingesting an isolated protein source at 0.24 g protein/kg and 0.40 g protein/kg in younger and older participants, respectively.
Given that the CI of this estimate spanned from 1.03 to 2.20, it may be prudent to recommend ~2.2 g protein/kg/d for those seeking to maximise resistance training-induced gains in FFM.
Basically, the older you are, or the more trained you are, the more protein you need both in total daily intake, and in per-meal doses. Who wudda thunk it?
The 1.6g/kg/day seems to be an average maximum effect dose across all age ranges, training sensitivities, training experience (novice vs advanced), training programs/styles (the meta analysis used papers that ranged from leg extensions only to powerlifting programs), etc. This produced a confidence interval high enough for the authors to warrant going upwards to 2.2g/kg/day to ensure maximum MPS, increases in 1rm, and muscle cross sectional area.
The studies also didn’t seem to account for protein quality (animal vs vegetable), although most of the protein supplemation seemed to be via whey or casein. So I would think 1.6g/kg/day is an animal based protein recommendation, making 2.2g/kg/day of protein from all sources seem a reasonable daily intake to ensure a maximum protein synthesis response. And this number may increase further the older, more trained, or ‘less male’ you are.