I read it when I was a teenager. It might be YA fiction, not sure as I had free run of the library and used to read from every section. It is based in the racing world and I think the main character was a young woman and part of it is about a jockey (possibly a real life person but it isn't a biography). I remember a part about the jockey trying to lose weight for a race.
I've been doing some googling but I don't have enough to go on.
Thanks