They might taste great going down, but they might bring up some gas later. "Seemingly innocent but potentially troublesome are mushrooms, which are high in polyols that can be fermented by intestinal bacteria causing gas," said Lauren Harris-Pincus, MS, RDN, author of The Protein-Packed Breakfast Club to POPSUGAR. Be mindful when eating them if you have a sensitive stomach, and note that portobello, shiitake, and button mushrooms are high in polyols, while oyster is lowest, she said.