Dairy proteins favor acute metabolic markers while pea protein may favor gut microbiota profilesDairy and pea protein offer different benefits for older adults

This narrative review comprehensively contrasts the physiological impacts of plant-based protein (focusing on pea protein isolates and matrices) vs. dairy-derived proteins (including intact casein and whey protein variants, emphasizing the rapid-digesting α-lactalbumin fraction). We establish a structured framework to separately report evidence from preclinical animal models and clinical human trials, evaluating acute (< 24 h) and chronic (>7 days) horizons across three domains: (i) neurocognitive function/mood, (ii) gut microbiota/hormonal responses, and (iii) aminoacidemia/metabolic–inflammatory responses in aging cohorts. Synthesized data reveal that preclinical animal models favor pea protein for altering gut microbiota profiles and elevating short-chain fatty acids, while dairy fractions, particularly α-lactalbumin, optimizing hypothalamic serotonin synthesis and neurocognitive performance via high tryptophan bioavailability. In clinical human trials, acute postprandial metrics heavily favor dairy fractions, inducing rapid leucine spikes and superior peripheral mTORC1 activation compared to pea protein. However, chronic long-term trials indicate that when absolute daily protein and essential amino acid requirements are met, often via leucine fortification or strategic plant–animal blending, discrepancies in muscle protein synthesis and physical performance between pea and dairy proteins are minimized. Ultimately, long-term functional adaptations depend primarily on total daily amino acid adequacy rather than protein origin. Due to a heavy reliance on male-skewed cohorts and a scarcity of direct head-to-head clinical trials comparing pea protein with pure α-lactalbumin fractions, caution must be exercised before making rigid clinical policy decisions for diverse, frail geriatric populations.