This enzyme completes each cycle of fatty acid elongation by catalysing the stereospecific reduction of the double bond at position 2 of a growing fatty acid chain, while linked to an acyl-carrier protein. It is one of the activities of EC 126.96.36.199, animal fatty-acid synthase. The mammalian enzyme is Re-specific with respect to NADP+. cf. EC 188.8.131.52, enoyl-[acyl-carrier-protein] reductase (NADPH, Si-specific) and EC 184.108.40.206, enoyl-[acyl-carrier-protein] reductase (NADPH).