The third list of foods are those that you really should avoid because these are all trigger foods that cause most people who suffer IBS problems to a greater or lesser extent.  In this category, you would include red meat, dairy products (even low fat yoghurt is likely to irritate your stomach), egg yolks, French fries, onion rings, croissants, pastries, biscuits and so on. In effect, anything that is high in unsaturated fats should be a no-no or at least make sure that you eat high-fat foodstuffs only very, very occasionally and that if you do so, you are prepared for some kind of adverse reaction.