A branched-chain amino acid catabolism enhancer and/or a branched-chain α-ketoacid dehydrogenase complex (BCKDC) kinase inhibitor (BDK inhibitor); or a meal replacement comprising low level of branched-chain amino acid (BCAA) for use in treating or preventing a proliferative disease in a subject in need thereof, wherein the branched-chain amino acid catabolism enhancer is a peroxisome proliferator-activated receptor-alpha (PPARa) agonist, wherein the PPARa agonist is at least one selected from the group consisting of propan-2-yl 2-[4-(4-chlorobenzoyl)phenoxy]-2-methylpropanoate (fenofibrate), 2-[4-[2-[(4-chlorobenzoyl)amino]ethyl]phenoxy]-2-methylpropanoic acid (bezafibrate), and 2-[4-[2-[4-cyclohexylbutyl(cyclohexylcarbamoyl)amino]ethyl]phenyl]sulfanyl-2-methylpropanoic acid (GW7647), wherein the BDK inhibitor is at least one selected from the group consisting of peroxisome proliferator-activated receptor-alpha (PPARa) agonist (such as propan-2-yl 2-[4-(4-chlorobenzoyl)phenoxy]-2-methylpropanoate (fenofibrate), 2-[4-[2-[(4-chlorobenzoyl)amino]ethyl]phenoxy]-2-methylpropanoic acid (bezafibrate)), and 3,6-dichloro-1-benzothiophene-2-carboxylate (BT2), and wherein the proliferative disease is characterized and/or diagnosed by at least one selected from the group consisting of: a suppression of transcripts-level of enzymes involved in the catabolism of at least one branched-chain amino acid (BCAA) when compared to a healthy control subject or group of control subjects; and a decrease in a level of an acylcarnitine (C5:1) when compared to a healthy control subject or group of control subjects; wherein the enzymes involved in the catabolism of at least one branched-chain amino acid (BCAA) are selected from the group consisting of branched chain keto acid dehydrogenase E1 alpha polypeptide (BCKDHA), acyl-CoA dehydrogenase C-2 to C-3 short chain (ACADS), and acyl-CoA dehydrogenase short/branched chain (ACADSB), wherein the branched-chain amino acids are leucine, isoleucine, and valine; and wherein the proliferative disease is selected from the group consisting of liver cancer, head and neck squamous cell carcinoma, kidney cancer, colon and rectum adenocarcinoma, breast carcinoma, lung carcinoma, thyroid carcinoma, stomach adenocarcinoma, and esophageal carcinoma. a suppression of transcripts-level of enzymes involved in the catabolism of at least one branched-chain amino acid (BCAA) when compared to a healthy control subject or group of control subjects; and a decrease in a level of an acylcarnitine (C5:1) when compared to a healthy control subject or group of control subjects; wherein the enzymes involved in the catabolism of at least one branched-chain amino acid (BCAA) are selected from the group consisting of branched chain keto acid dehydrogenase E1 alpha polypeptide (BCKDHA), acyl-CoA dehydrogenase C-2 to C-3 short chain (ACADS), and acyl-CoA dehydrogenase short/branched chain (ACADSB), wherein the branched-chain amino acids are leucine, isoleucine, and valine; and wherein the proliferative disease is selected from the group consisting of liver cancer, head and neck squamous cell carcinoma, kidney cancer, colon and rectum adenocarcinoma, breast carcinoma, lung carcinoma, thyroid carcinoma, stomach adenocarcinoma, and esophageal carcinoma. <EOS>