Why do I get such bad gas after eating?

IANAD, probably worthless advice: it sounds like you've already ruled this out but are you sure it isn't something as simple as lactose intolerance? Better advice: Reconsider seeking medical help. My bro had a similar problem (though not, apparently, as bad as yours -- yowzers!) which was solved by a visit to his campus health office, and then the doctor they referred him to.

You don't mention what your healthy diet consists of, but if I were you, I'd start keeping an extremely detailed food diary, and then go to your doctor with it. S/he might send you to an allergist--this could very well be a sign of a food allergy. Flatulence is a symptom of all sorts of things--celiac disease and leaky gut syndrome spring to mind. (Though flatulence is only one of several other much less pleasant symptoms, so it's probably not one of those.) If you don't have the money to see a doctor, then I'd recommend--after you've kept the diary for a week or two--subtracting things from your diet to see if you can determine what's causing the gas.

You say you don't drink soda, but do you drink a lot of sweetened fruit juices or chew gum (particularly sugar-free)? Could be http://health.yahoo.com/ency/healthwise/_aa113455.

I almost always eat a bowl of raisin bran or mini-wheats in the morning. Wow, you nearly just answered your own question there. Get off the high-fiber cereal for 2 weeks, then report back. Even though you say you don't get gas after breakfast, I don't think that means the high-fiber cereals aren't affecting your digestion throughout the day. In my opinion, these sorts of things (along with any excessive quantities of vegetables, or any vegetables that haven't been cooked until very well done) would be the first things to remove in trying to treat the flatulence.

rxrfrx has a good point. Swap out the bran cereals for oatmeal for a few weeks, and think about your fiber sources in general -- you may be getting too much insoluble fiber at the expense of adequate soluble fiber. You really need http://www.hsph.harvard.edu/nutritionsource/fiber.htmlfor optimum digestion.

I have this exact problem too.... it's from milk. Eliminate all milk and dairy from your diet for two or three days. If your problem goes away, that's it. You don't even really have to change diet... just start taking lactase with your milk. Don't buy brand-name Lactaid, it's overpriced... the drugstore generics are excellent. I like the Ultra type. They're cheaper, because you only need 1 for most meals. The 'regular' kind takes 3 caps for the same effect.

Sounds like an imbalance of microflora in your intestine. I was on high dose oral ciprofloxin (a broad spectrum antibiotic - btw, are you taking anything like that?) for a while - killed a bunch of "good" gut bacteria and I had prodigious, severe, and odious gas. Went away after I stopped the cipro. Ask your doctor about probiotics or eat some dirt.

chiming in again to say that PurplePorpoise's suggestion about probiotics (like http://www.wholefoodsmarket.com/healthinfo/wholehealth/acidophilus.html) is also a great one. Get a sufficient dosage (at least 1 billion organisms per capsule) and store it in the fridge. It's worth mentioning that acidopholus can actually increase gassiness for a couple of days when you start it, but don't be alarmed -- stick with it for a week or two and see if you get some results.

I don't think that the amount of fiber in Raisin Bran or Mini Wheats could be causing such severe gas, plus the problem is cyclical and the cereals are something you eat consistently. There's a very good chance that your problem is related to a wheat or dairy intolerance, as others have suggested above. I would try cutting out all wheat and dairy for a few weeks. Then if that helps, you can add back one or the other to determine which is causing the problem. Also, scody makes a great point -- if you chew gum or use artificial sugars for anything, it's a good idea to leave that stuff alone too. Sorbitol and malitol (which are found in most popular chewing gums, especially those super-strong icy-mint kinds) totally wreak havoc on my digestion. If I chew one piece of that type of gum, I have a stomachache for days. Also, try and stick to simple whole foods where you can. If your digestive system is already stressed, you don't need a lot of hard-to-digest chemicals and additives to complicate things further. And if those things don't help, you could see a gastroenterologist or a dietitian. Good luck!