The whole poem hangs on a pun. "Go to fat" sounds like "go to fat," as in letting yourself go, but "dine to lose me" twists the usual diet logic. Here the speaker eats not to lose weight but to lose the self, the "me." The title, "(W)hole," shows the trick: the word holds both "whole" and "hole," and the parentheses let us see the "W" drop away.
So there's a double meaning in the eating. The speaker feeds a hunger, maybe an emptiness, and the more they dine, the more the "whole" grows. Yet a hole is also what's being filled, or perhaps what's being made. The "me" shrinks while the bulk increases.
The mood is wry and a little uneasy. It's playful on the surface, with its wordplay and tiny length, but there's something bleak underneath. The poem suggests someone using food to disappear into something bigger, and the joke starts to feel like a confession.