In Carter Dickson’s 1940 novel And So to Murder, Hollywood scriptwriter Tilly Parsons swears by a diet of lamb chops and pineapple as a great way to take off those extra pounds. (Her colleague Bill Cartwright calls it a “hellish combination”.) I assumed John Dickson Carr was parodying fad diets and had just made up an unlikely combination when I read this passage, but I’m in the middle of rereading Anthony Boucher’s 1941 The Case of the Solid Key, and at one point Fergus O’Breen suggests he and Norman Harker have lunch at a movie studio commissary: “Watch buxom blondes, brooding brunettes, and ravishing redheads – all eating lamb chops and pineapple?”
So I checked Wikipedia and sure enough, “lamb chops and pineapple” was a real fad diet back in the day! Apparently the idea was that the protein in the lamb and the sugar in the pineapple would give you strength, while the acid in the pineapple would dissolve the fat in the lamb, or something like that. Like so many fad diets, it turned out to be unhealthy because eating just two foods meant you were missing out on a lot of essential nutrients.
The things you learn reading classic mysteries!