The function of ECH1 (enoyl-CoA hydratase 1, Ensembl gene identifier ENSG00000104823) is as follows. Auxiliary enzyme in the beta-oxidation of mono- and polyunsaturated fatty acids (PubMed:26474213). Together with the 2,4- dienoyl-CoA reductase (DECR) and the Enoyl-CoA delta isomerase 1 (ECI1) they allow reentrance of the enoyl-CoA into the beta-oxidation cycle (PubMed:26474213). Able to isomerize 3-trans,5-cis-dienoyl-CoA (3E,5Z- dienoyl-CoA) to 2-trans,4-trans-dienoyl-CoA (2E,4E-dienoyl-CoA), a crucial step in the beta-oxidation of unsaturated fatty acids with double bonds at odd position (By similarity) (PubMed:26474213). Based on its established catalytic mechanism, it is predicted to act also on other fatty acids besides those tested experimentally (Probable). {ECO:0000250|UniProtKB:Q62651, ECO:0000303|PubMed:26474213, ECO:0000305|PubMed:26474213}.