The Digestive system is the bodily system that serves the purpose of breaking food down into its nutritional components.
When Lwaxana Troi was attracted to Odo in 2369, he attempted to lose her interest in that he couldn't eat as he did not have a digestive system. (DS9: "The Forsaken")
The Doctor was going to have a present topic on Hints for Healthful Living about the Bolian digestive system. (VOY: "Investigations")
Both the USS Enterprise and the USS Voyager have been almost eaten inside of the digestive systems of spaceborne species. (TAS: "One of Our Planets Is Missing"; VOY: "Bliss")
Parts of the digestive system