Isomorphs did not need nourishment, nor suffer disease. The holographic matrix of an Isomorph was also known as an isomatrix. Dejaren demonstrated an ability to cause pain in organic lifeforms by intersecting his arm in their body.
While isomorphs were still considered holographic beings and their technology was potentially fairly compatible with Federation holographic technology, isomorphic projections were more advanced, as Think Tank member Kurros, while interacting with Captain Janeway on board Voyager in such a form, was actually able to taste a cup of coffee, despite only appearing in isomorphic form at the time. (VOY: "Revulsion", "Think Tank")
In 2374, B'Elanna Torres and The Doctor encountered an HD25 Isomorphic Projection named Dejaren, who worked as a laborer aboard a Serosian spacecraft. Responding to a distress call in which Dejaren claimed that his entire crew of six Serosians had been killed by an illness, they soon discovered that Dejaren had, in fact, murdered the entire crew. Dejaren subsequently attempted to kill Torres and steal The Doctor's mobile emitter, but his matrix was destabilized when Torres exposed him to a isomagnetic conduit. (VOY: "Revulsion")
In 2375, Kurros communicated from his ship, hidden in subspace, via isomorphic projection. He used this method to communicate with Captain Janeway aboard Voyager, in an attempt to offer assistance in solving the problem of constant attacks by the Hazari. Janeway was later able to deny him the ability to do so further by ordering Voyager's shields remodulated to a phase-variant frequency. (VOY: "Think Tank")