The answer may surprise you and I'll reveal it at the end of this post.
What I really want to talk about is how crunches are literally a pain in the neck...and the back. There are some schools of thought that the spine has a finite number of times it can go into flexion. Whether or not its true, the abdominal muscles and "core" muscles are meant to stabilize the torso, not necessarily flex the spine.
Now what should you do, since I'm telling you to take crunches out of your program? There a tons of things to do that can help activate and make your "core" stronger. Planks and side planks are a great place to start. While they may be boring, they are a great way to develop stability throughout the body. Think about it, picking up something off the ground, your core muscles must contract to keep the body in one straight line. Try it.
Now if those exercises get too easy for you, try adding movement to them. The body doesn't really work while being stationary, so adding movement translates well into real life. Planks while moving the arms or legs, reaching with the arms in multiple directions, adding rotation, crawling, pulling or pushing objects, and even using a Swiss ball can all add an additional challenge while trying to stabilize the body.
Want one of the best core exercises out there? Try a Turkish get-up. Super amounts of stabilization necessary, not only from the core muscles, but from the shoulders as well.
Ok so now for the answer to the question from the beginning of the post. It takes 22,000 crunches to burn that 1 pound. Don't take that as a challenge, do something else.