The digestive tract or GI tract was a large component of the digestive system, made up of a series of organs that makes up the upper intestinal tract (including the esophagus and stomach) and the lower intestinal tract. It was responsible to the taking in food, digesting nutrients and energy from it, and expelling its waste in the form of feces and urine.
In discussing the consumption of Human food with Phlox, T'Pol stated that she preferred Vulcan food because she had "sampled Human food on several occasions" and noted that "it didn't agree with me". Phlox, nevertheless, encouraged her to "give it some time", reminding T'Pol that "the Vulcan digestive tract is highly adaptable." (ENT: "Unexpected")
Following his transformation from Human to Loque'eque, and being restored to Human once again, Malcolm Reed asked Dr. Phlox if that he had anything for his stomach, because "the Chef's food isn't sitting too well." Phlox, rather, informed Reed that "till your digestive tract is fully restored, you may want to avoid the mess hall." (ENT: "Extinction")