TABLE 1.

PICOS statement that guided the systematic review

Parameter	Inclusion criteria	Exclusion criteria
Population	Older adults with or without sarcopenia or frailty (older than 60 years) and without any other overt disease that may affect the outcome	Participants with medical conditions affecting outcome measures, such as cancer, diabetes, chronic obstructive pulmonary disease, and neurological disorders (e.g., Parkinson or dementia)
Intervention	Whey protein supplementation (with or without exercise training), and whey protein and vitamin D co-supplementation (with or without exercise training)	Interventions with special diets such as the ketogenic diet or co-supplementation with other nutrients or active ingredients with possible effects on LBM (such as omega-3, vitamin E, creatine, and casein)
Comparator	No intervention (control) or isocaloric and nonisocaloric placebo (carbohydrate based)	No control group or protein-based placebo (such as soy or milk protein)
Outcome	Sarcopenia-relevant measures, such as lean mass or appendicular lean mass, OR muscle strength (upper body strength: handgrip or lower body strength: leg press or knee extension), OR physical function [gait speed (m/s)], SPPB score, or TUG, time stand, chair stand, balance test, sit-to-stand, and walking tests	Not reporting any of the outcome measures
Study design	Randomized control trial (RCT)	Not an RCT

Abbreviations: SPPB, Short Physical Performance Battery; TUG, timed up-and-go.