Well diet alone may not control it but usually people do this a few way.The act of eating may set off symptoms for a lot of people.Foods that make constipation better tend to make diarrhea worse, so depending on which side you are, you may need to adjust.1. Eliminate every thing for about two weeks then add foods back one at a time.So something like rice, chicken, zucchini and canned/cooked pears. Water to drink, and some people will add coffee or tea if you need the caffeine (drink black/plain) as you don't want to mistake caffeine withdrawl for continued symptoms, but some people with IBS are very sensitive to caffeine. Some people will use the BRAT diet as their basic diet but bananas, rice, applesauce toast may not be varied enough for long term, and some people have issues with wheat so maybe a BRA diet would be better.2. Cut back/eliminate the likely triggers for diarrhea or gasA-Fatty Greasy or fried foods including red meat or the skin of poultryB-Raw Fruits with sorbitol in them or the juice of those fruits (as well as sorbitol added to processed foods and gum, and this is really anything ending in-itol) So apples, pears, peaches, plums/prunes, cherries, apricots. C-Raffinose containing foods. Beans, Soy, Cabbage Family Veggies.D-Wheat (makes a lot of people gassy, but not a problem with diarrhea)E-Lactose or fructose (so fresh dairy--aged cheeses OK if low fat) and I'd start with no High Fructose Corn Syrup added to foods and no Honey. Cane sugar is better for most people if you need a sugar in things. you may need to stick to berries and citrus for fruits with this and limit amounts per mealF. Caffeine and AlcoholSome people do well on a diet high in soluble fiber so usually the processed grains or oats and rice but again some people get too gassy from theses.Some people do well on any generally low starch diet like most low carb diet plans.3. Eat the way you always do but keep a journal and log symptoms.A lot of people just do number 3 and see if anything shows up. This works better if you don't have the same symtoms every meal no matter what you eat. If you react to the act of eating, just do small frequent meals of 300-400 calories maximum at a time. A lot of people react to the stomach being filled, not which food fills it.