I’m not a doctor, so don’t take my word for it, but I’ve heard the same as robolemmy. To be a bit less abstract, my understanding is you eat enough so that your stomach will digest normally instead of just handling the medicine as a tiny bit of something caustic. A granola bar should be fine, but you might do better with a slice of bread or something a tad easier to digest. Then again, I don’t think it matters all that much.