Ok, you ask "Do they even have one?"(digestive track)...Um, they eat , they poop...so thats a digestive track.
The flakes you feed your gold fish don't look like flakes when they come out do they?
Vary your goldfish's diet. It's healthier and less boring probably for the fish. Flakes are ok as the staple in their diet, but adding bloodworms, shrimp, peas even bits of oranges and pelleted food will vary their diet some.
Any frozen peas are just fine. You can take a couple and cut them in half and throw them in the tank. My fish suck them right out of the shell. I use a small net and collect the skin or shell later.