Elevation by Stephen King

When a man starts losing weight (but not getting any smaller), he uses the strange situation to subtly affect change in his small town.

When we meet Scott, he's embroiled in a nasty disagreement with his lesbian restauranteur neighbors about their dogs pooping in his yard. He's super-busy with a big project for his website development business, but unhappily divorced and lacking human connections. He visits with a retired doctor about the weight problem, not because he thinks there's a cure but because he wants someone to confide in.

As his health problem becomes more extreme, Scott takes on "fixing" things with his neighbors as a project. A sort of quest, as you may.

I had a hard time starting this book - I actually read the first 30 pages twice, because I'd set it down for quite a while and had to begin again. But once I got into it, I was hooked. It's a modern parable about the "weight" of one person on a community. Bonus: I had no idea what would happen in the end!