Some info, not very pleasant:
Lar has found--by experience, unfortunately--that certain sugars can lead to diarrhea and intestinal distress. Malitol (used in sugar-free candy) can affect him with a single piece. Sorbitol (also used in sugar-free products like chewing gum) often causes the same problem.
He was told by his doctor to watch out for ingredients ending in -tol, as they were usually sugar substitutes and would most likely cause the same problem for him.