INS and diabetes mellitus: Patients with impaired glucose tolerance (IGT) have reduced levels of phenylacetyl-glutamine and increased levels of acylcarnitines and α-ketoglutarate, a pattern indicative of TCA cycle intermediate depletion which interferes with insulin action23, as well as reduced tryptophan, xanthine, methionine and nucleotides; patients with diabetes also have a higher plasma level of octanoylcarnitine compared to non-diabetic individuals24.