While the assessment of plasma profiles of AC and amino acids is currently utilized for the early diagnosis of inherited disorders of fatty acid catabolism including medium and very long chain acyl-CoA dehydrogenase deficiencies, disorders of amino acid catabolism such as phenylketonuria and maple syrup urine disease, as well as organoacidurias (e.g. isovaleric acidemia) [48], the growing number of studies has provided evidence also about the involvement and/or influence of AC and amino acids with regard to development of insulin resistance ([3, 4, 49], and reviewed in [50]). This evidence concerns the gene ACADL and phenylketonuria.