The present invention relates to compositions suitable for the treatment of pathological conditions distinguished by insufficient or reduced mitochondrial function. The compositions comprise, as principal active ingredients, the amino acids leucine, isoleucine and valine. The compositions may also comprise, as further active ingredients, amino acids threonine and lysine, and optionally, histidine, phenylalanine, methionine, tryptophan, as well as tyrosine and cysteine.