Table 4 Characteristics and key findings of previous systematic reviews which aimed to identify the importance of protein source for muscle health outcomes

Langer & Carlsohn, 2014 [26]

< 40

Any two protein sources consumed within 90 min of RET

Muscle mass

A combination of whey and casein milk proteins can provide the most perpetual anabolic effects

Messina et al. 2018 [27]

≥ 18

Soy protein vs animal protein (+RET)

Muscle mass

Strength (squat and bench press)

Soy and whey protein were found to have similar effects on lean mass accretion and strength (for both squat and bench press)

Lim et al. 2021 [28]

≥ 19

Plant protein vs animal protein (with or without RET)

Muscle mass

Strength (squat, bench press, grip strength, peak flexion/extension of leg)

A nonsignificant favourable effect of animal protein on absolute lean mass was seen, and in the subgroup analysis based on age, an anabolic effect was only observed in the younger populations (< 50 years). No statistical difference between plant and animal protein was seen for strength outcomes aside from a favourable effect of animal protein on leg extension in the younger subgroup