Quinn has 4 tasks - The valve puzzle, the vat puzzle, the broken conveyor, and the maze in the bottom left. It sounds like you missed the broken conveyor, so try interacting with stuff around there.
Sorry, I meant by how do you go through it without getting so fat. I was able to finally figure the valve puzzle and the broken conveyor (somehow skipped the tile that had the prompt), but you get a lot of fat through the maze (not to mention the catwalks giving a lot by going through them as well as the gas in the sewers being very aggressive in hitting you with more fat).
Then again since an ending isn't available I don't see why to consume every possible food item.