"I had to have a six-pack on show," Matt told the U.K.'s Sunday Mirror (via People). "The potato acts as a sponge and your body literally shrinks and gets ripped and tight." So that’s how he stays so cut.
Not that Matt relies only on sweet potatoes. “Afterwards I ordered two pizzas and pasta!" he said of letting go post-shirtless Glee scenes. We don’t blame him!