Background:Protein-energy malnutrition is a major cause of functional decline in the elderly and isclearly an important component of frailty. However, limited evidence is available about how to select frailindividuals most benefiting from protein-energy supplementation. Objectives:1) To investigate factors associatedwith stronger benefits from protein-energy supplementation, and 2) to test the hypothesis that the severity offrailty is associated with the efficacy of protein-energy supplementation. Design:Secondary analysis of data froma pre-post-intervention study and a clinical trial. Setting:National Home Healthcare Services in Gangbuk-gu,Seoul, South Korea. Participants:123 community-dwelling frail older adults [usual gait speed (UGS)