Gastrointestinal distress was a term to describe an unpleasant, and not always serious medical condition involving the digestive tract.
In 2151, Porthos suffered from mild gastrointestinal distress, caused by Jonathan Archer having fed the dog with cheese. (ENT: "Dear Doctor")
In 2152, Malcolm Reed suffered from gastrointestinal distress due to the spatial turbulences caused by a neutronic wavefront. He received a hypospray from Doctor Phlox (ENT: "The Catwalk")
Following USS Voyager's arrival in the Delta Quadrant in 2371, efforts to conserve replicator energy included having Neelix operate the kitchen, one side effect of which, was complained by Tom Paris to Captain Kathryn Janeway, when he said how he was sure that the gastrointestinal problems would go away "as soon as our digestive systems got used to his, er, gourmet touch." (VOY: "The Cloud")
Later the follow year, when the lifeform Tuvix was created, The Doctor explained how they could separate the DNA of Tuvok and Neelix by using a procedure using a concocted isotope that would work how barium used to work with X-ray technology. The method he drew his idea from was one that ended in the late 21st century, whereas "physicians administered barium to patients with certain gastrointestinal disorders" and the radioactivity of the barium "made the lining of the intestines visible" on X-rays. (VOY: "Tuvix")
In 2376, Tuvok suffered from space sickness also caused by a a neutronic wavefront with the symptoms being gastrointestinal distress and a loss of equilibrium. (VOY: "Fair Haven")