I once read a short story about a few ships from Earth who were sent out to either find a better planet or help humanity in some way. The fleet encounters another alien ship (that had malfunctioned? or were in conflict with?) and the captain of one of the Earth ships decides to bring aboard the alien crew. These end up taking over the ship and seem fascinated by the humans.
At one point one of the alien underlings can't help but smell one of the human's hair and becomes almost crazy with the smell. Its superior tells him to stop. There's a general subterfuge going on and you start to realise that the aliens have an insatiable appetite for human protein.
The captain decides to side with the aliens so as to not get eaten. The aliens take the surviving crew of four in the human ship back to their planet and recall all of their ships as they have realised that there's a whole planet (Earth) worth of protein which they plan to invade and feast on.
They host a planet wide party as finding humans means they will have plenty to eat. Apparently they had exhausted all of their food supply and were surviving only on synthetic supplements. The captain realises the impending doom for all humanity and as a last heroic act turns on the ship's engine (which was only designed to be turned on in the vacuum of space) and it causes a chain reaction which obliterates the alien planet and causes xenocide...and saves humanity.
Can anyone remember the author and name of this story? Looking at my cat I can't help but see a parallel...