Required for branched-chain fatty acid synthesis (such as (omega-1)-methyl-fatty acids) (PubMed:18390550). Catalyzes the reduction of the 3-keto-fatty acyl-CoA intermediate that is formed in each cycle of fatty acid elongation (PubMed:18390550). Very long-chain fatty acids (VLCFAs) serve as precursors for ceramide and sphingolipids (PubMed:12905072, PubMed:18390550, PubMed:21926990). Involved in hormone production as it metabolizes 4-androstendione (androst-4-ene-3,17-dione) into testosterone and estrone into estradiol (17beta-estradiol) in vitro, but the physiological steroid substrate is unknown (PubMed:17951538). a very-long-chain (3R)-3-hydroxyacyl-CoA + NADP(+) = a very-long-chain 3-oxoacyl-CoA + H(+) + NADPH (omega-1)-methyl-(3R)-hydroxy-fatty acyl-CoA + NADP(+) = (omega-1)-methyl-3-oxo-fatty acyl-CoA + H(+) + NADPH a 17beta-hydroxy steroid + NADP(+) = a 17-oxo steroid + H(+) + NADPH Lipid metabolism; fatty acid biosynthesis. Expressed in the gut of larva and adult. Expressed from first larval stage to adult. Worms exhibit slow and retarded growth, reproductive and molting defects, defects in embryogenesis, and hypersensitivity to cholesterol limitation (PubMed:12905072). Increased polarity and tubulogenesis defects in an allelic series of let-767 (PubMed:21926990). Belongs to the short-chain dehydrogenases/reductases (SDR) family. 17-beta-HSD 3 subfamily.