Here are some of the best food metaphors in the interest of horror that the CC knows of in the medium of film.
Slaughter as a metaphor for the ruthless elimination of an entire generation in World War I.
Bonus: Made in 1939. Looks forward presciently and sees a repeat upcoming.
If you can make tea horrifying, you have real cinematic skill.
Bonus: The Lipton tea ad-placement near the end of the movie.
It's straightforward enough to horrify using a skinned putrefying rabbit but it takes a special talent to turn toast and (exhausted) marmalade into one for a horrific sexual frigidity gone awry.
The perfect meeting of medium and subject. Integrated into the film as a logical progression of horrors, Pasolini mentioned that he intended it as a "commentary on the horrors of fast food".
(You'll have to see this one. Can't reveal it without giving it away.)