BACKGROUNDSoy-based meat alternatives (SBMA) are becoming increasingly popular, but it is unclear if they have the same anabolic effect on skeletal muscle as animal meat. OBJECTIVEWe aimed to compare the stimulation of skeletal muscle protein synthesis by consumption of one or two 4 oz patties of SBMA with 4 oz (80%protein/20%fat) beef. METHODSThe study design was a randomized controlled trial. Participants were aged 18 to 40 years of age and in good general health with a BMI between 20 and 32 kg/m2. Stable isotope tracer methods were used (L-[ring-2H5] phenylalanine, [U-13C9-15N]- tyrosine and L-[ring-2H4] tyrosine) to quantify the response of muscle protein fractional synthetic rate to consumption of a single beef (4 oz), single SBMA (4 oz), or two 4 oz SBMA patties (8 oz). Whole-body rates of protein synthesis, breakdown and net balance, as well as plasma essential amino acid (EAA) concentrations, were also measured. RESULTSThe increase above basal in muscle protein FSR following consumption of the 4 oz beef patty (0.020 ± 0.016%/hour) was significantly greater than the increase following consumption of 4 oz SBMA (p = 0.021; 0.003 ± 0.010%/hour) but not 8 oz SBMA (p = 0.454; 0.013 ± 0.016%/hour). The maximal EAA concentration was significantly correlated (p = 0.046; r = 0.411) with the change in muscle FSR from the basal to postprandial period. In addition, the change in muscle FSR from the basal to postprandial period was significantly correlated (p = 0.046; r = 0.412) with the corresponding change in whole-body protein synthesis. CONCLUSIONConsumption of a 4 oz beef patty stimulates muscle and whole -body protein synthesis more than a 4 oz SBMA patty and similarly to 8 oz of SBMA. Trial RegistrationClinicalTrials.gov Identifier: NCT05197140