Experimental design
RECRUITMENT, BLIND
Experimental testing was divided into 2 phases, with participants assigned to 1 of the 2 parallel dietary intervention groups by the lead investigator, using simple randomization, which differed only with respect to the primary sources of dietary protein consumed throughout the study: omnivorous (OMNI) or vegan (VEG). Participants who continued involvement from Phases 1 to 2 of the study retained their initial randomization from Phase 1. Four participants declined to participate in Phase 1 of the study, but were assigned to Phase 2 of the study in an attempt to increase the sample size to account for attrition, potential insufficient muscle sample size, and/or loss of samples during analysis. The study was an open-label design, therefore, it was not practically possible to blind the participants or the investigators. Analysis was performed in a blinded manner, with the exception of body composition and strength data in which the real-time nature of these measures precluded blinding. If a participant’s habitual dietary choices (that is, vegan) precluded their inclusion in the omnivorous group, they were assigned to the vegan group (and therefore not randomized) (Flow chart of participant recruitment and allocation within the 2 phases of the experimental protocol. IHC, immunohistochemistry; OMNI, omnivorous; VEG, vegan.Schematic representation of the study protocol. Phase 1, 16 healthy young adults consumed a 3-d fully controlled, eucaloric, and high-protein (1.8 g·kg bmTo allow for a controlled assessment of dietary protein source on free-living, daily MyoPS rates in line with our previous work [Phase 2 examined how the dietary protein source affects the longer-term muscle adaptive responses and consisted of 10 wk of dietary manipulation alongside 5 × per wk-structured resistance exercise. The participants in the OMNI2 group were counseled to consume a high-protein omnivorous diet, including milk protein supplementation, and those of the VEG2 group consumed an exclusively non–animal-derived diet, including mycoprotein supplementation. Muscle fiber cross-sectional area (CSA), DXA whole-body lean mass, and MRI thigh muscle volume were determined pre, after 2 and 5 wk, and post-intervention, with muscle strength and muscle function determined pre and post-intervention.