If you have diarrhea-based IBS, then you should avoid the following food items: - Fried foods - Fatty foods - Dairy for lactose intolerant people - Foods containing wheat if you're gluten sensitive - Too much fiber - Chocolate - Carbonated drinks - Caffeine - Alcohol Foods that make your symptoms worse if you have constipation-based IBS: - Processed foods - Refined grains - Dairy - Too much protein - Carbonated drinks - Caffeine - Alcohol Many doctors recommend their patients follow the low FODMAP diet, so do talk to a dietician about it.