Sarcopenia and probable sarcopenia are associated with loss of muscle strength, functional impairment, frailty, and an increased risk of adverse outcomes in older adults. In short-term interventions, structural or functional changes may be modest, whereas certain serum biomarkers of metabolic-nutritional response may be more sensitive. In this protocol version, serum transthyretin (TTR) has been selected as the primary outcome, without assuming that it represents, by itself, a direct measure of muscle mass or overall clinical efficacy.