A method of treating or preventing depression using β-hydroxy-β-methylbutyrate (HMB) is described. The method includes administering an effective amount of HMB or a pharmaceutically acceptable salt thereof to a subject in need thereof. The HMB can be administered as part of a nutritional composition. Also provided is a method of treating or preventing a condition which can be improved or prevented by the activation of mTOR signaling by administering an effective amount of HMB or a pharmaceutically acceptable salt thereof to a subject in need thereof.
