Under its darkly comic surface, "Diet Plan" is a list of New Year's-style resolutions that slowly turns sinister. The speaker begins with silly sacrifices, like giving up wings and hambones, but the jokes sour quickly. Human beings are "the other white meat," and soon he is giving up salt, bread, truth, and tenderness, keeping only "the caress of the knife," which silences a mouth.
The speaker seems to want a life without memory or conscience. He swears off history and longs for a "perpetual present" that he calls wartime, a state of constant alertness and violence. His model is a skinny barn cat dodging rain, and the poem ends by turning rain into "God's own ordnance," or bombs.
The mood is chilling, sardonic, and unsettling. The cheerful, bureaucratic tone of a diet makes the brutality feel colder. The poem seems to show how easily someone can talk himself into cruelty by treating it as self-discipline.