Marked question

I've read another book that was similar to this one with a hero from another world/realm with the heroine being on earth but only being part human (which may have been making her sick or weak? i think)and they're fighting off some kind of monsters/demons whatever.. but about the only other thing that i can remember is that eating food and drinking water from the other world/realm gives the heroine more strength, makes her feel better.. does that sound familiar to anyone?.. i thought it was in this book and kept waiting for that to be brought up as i listened to the audio book (i'd only read the ebook once before and it was a long time ago) so when it never happened it started to bug me cause i can't remember what book that it came from.. can anyone help me?