This happened for real, actually, at least some german science fiction publishing houses did that. They would "insert" a page into the book, which picks up the story in some really cheesy way and then bends in within two sentences towards the main character needing a quick soup now (the advertise was for soup always, they just had that one sponsor apparently).
The introduction goes like: "Only Kirk kept helping himself, because he was convinced he would need strength for the upcoming events." and then below the black bars the actual ad: "The reader should do same bla e.g. soup bla takes just 5 minutes etc"
See here (picture gallery): https://johannes.freudendahl.net/2019/01/werbung-in-romanen/
The introduction goes like: "Only Kirk kept helping himself, because he was convinced he would need strength for the upcoming events." and then below the black bars the actual ad: "The reader should do same bla e.g. soup bla takes just 5 minutes etc"
Just some anecdote.