The speaker has just finished a meal, and the title tells us it belongs to the "Paleolithic diet," the eat-like-a-caveman approach built around meat. The "gory victual" is a bloody, barely tamed piece of food, and the word "victual" is old-fashioned, which adds a comic edge. Eating like a cave dweller, but with such a formal word.
The punch comes in the last line. The speaker hopes to "get thin / being full of solution." It's a pun: "solution" can mean the answer to a problem, like losing weight, but also a liquid in which something is dissolved. The speaker imagines digestion as a kind of dissolving, with the heavy meal breaking down into liquid.
The mood is light, dry, and a little wry. The speaker sounds both hopeful and slightly absurd, laughing at the way a diet promises easy answers. The short lines make the poem feel like a quick aside after dinner.