Use of a ketone body and a ketone body ester for preserving glycogen and/or protein, thereby reducing muscle breakdown and improving endurance during exercise and promoting muscle recovery following exercise. Also for retarding muscle wasting in aging and disease. (R)-3-hydroxybutyl (R)-3-hydroxybutyrate for use in reducing muscle glycogen and protein breakdown during exercise or decreasing muscle wasting in aging and disease. Certain esters of hydroxybutyrate monomers, particularly a monoester of D-ß-hydroxybutyrate with R-1,3-butanediol or with glycerol to reduce muscle breakdown and aid muscle recovery after exercise or retard muscle wasting. Compositions containing the ketone bodies or ketone body esters are also described.
