Had IBS (starts with C, immense gas pains, then D) most of childhood, teenage and young adult life and this works for me. Still triggered every now and again when I travel or have late meals or odd beer.

• very routine times for breakfast 730 lunch 12ish and dinner 6ish
• 1 coffee in morning 1 decaf in afternoon
• dramatically cut down sugar, no alcohol, no red meat, cut spice (blander meals no curries), very little snacks, avoid diary, avoid starchy carbs
• naturally eat a lot of leafy veg and less meat, which I love and grown
• only very occasionally use natural laxatives (fybogel)
• daily probiotic tablet and yogurt
• light dinners and no heavy meals after 7pm. Heaviest meal is lunch with meat veg and a carb (usually rice or rice noodles)

I am underweight but healthy. My only downside is socialising especially explaining why I don't want to drink or ordering only a starter.