Comparative effects of dairy, hybrid and plant-based protein blends (including fibre fortification) on amino acid profiles and gut microbiota adaptations: The Promephy study.

This study investigated the acute and sustained effects of different protein interventions on postprandial amino acid profiles, uremic toxins, faecal fermentation metabolites and microbiota composition in healthy volunteers. Sixteen participants (7 males, 9 females; mean [SD]: 37 [9] years; 69.4 [10.2] kg; 1.74 [0.08] m) completed four 2-week intervention periods, separated by a 6-week wash-out. For each intervention, participants were allocated 50 g d-1 protein from either a milk protein isolate (MPI), a hybrid blend (HYB), a plant-based blend (PB) or a PB blend with added mixed fibres (PBF) in addition to habitual dietary intake. Pre and post intervention, participants underwent laboratory assessment of amino acid profiling (4 h post consumption of 20 g protein from the allocated product), along with stool sample collection for microbiota sequencing. Plasma essential amino acid (EAA) profiles and incremental area under the curve (iAUC) were lower for both PB products at baseline compared with MPI and HYB (MPI: 89,397 [18,025]; HYB: 87,301 [16,920]; PB: 65,350 [17,111]; PBF: 66,595[20,827] μmol·240 min L-1, p < 0.001). Following intervention, EAA profiles decreased further with both PB products, remaining lower than both MPI and HYB (MPI: 83,038 [20,983]; HYB: 76,341 [16,741]; PB: 56,075 [17,045]; PBF: 56,170 [15,213] μmol·240 min L-1, p < 0.001). After the 2-week intervention, L-leucine iAUC was lower for all products compared with MPI (MPI: 19,219 [4444]; HYB: 16,776 [3291]; PB: 12,003 [3008]; PBF: 11,948 [2991] μmol·240 min L-1, p ≤ 0.016), highlighting the importance of fortification or increased protein intake with PB containing products. PB inclusion into products resulted in minor increases in indoxyl sulfate within-intervention (p ≤ 0.039) which may be potentially beneficial in lower concentrations. Both HYB and PBF interventions resulted in increased saccharolytic metabolite production in relation to proteolytic metabolites (p ≤ 0.008). PBF resulted in a significant reduction in Peptostreptoccaceae compared to all products (p ≤ 0.007), as well as an increase in Marinifilacaeae (p = 0.014), which may support gastrointestinal health. The inclusion of fibre into protein interventions may therefore be beneficial for modulating metabolic 'fates' of protein, as well as supporting relative taxonomic changes which may regulate gastrointestinal integrity and function.