Confession time, folks: I am now, and I've always been, a celiac, and for those who just muttered, "I knew he was a weirdo," I must tell you that although my family agrees with you, a celiac is not always a weirdo. Rather, it's someone allergic to gluten, a protein found in certain grains including, unfortunately, wheat, rye, and barley. (There's controversy about oats and buckwheat, so I've always avoided those grains, too.)
Many of you will instantly realize that to avoid gluten-containing grains, you must not eat bread, pastry, pasta, and cookies (unless they're made of flour from "safe" grains, such as rice, corn, or (uk!) soy). But what you may not realize until a sad but wise celiac tells you is that other foods that often contain gluten include beer, soy sauce, ice cream, sauces, soups, luncheon meats, and many others, because wheat flour is often used as a "filler" - the industry spin word is "extender" - in such products.
Happily, most celiacs get away with eating "glutenous" foods occasionally (although some are so sensitive that even a bit of cheating leads to problems). But what should keep all celiacs toeing the line as much as possible is this: symptoms (usually related to the gut - diarrhea, cramps, and so on) can recur at any time and be severe; the gut can be so stripped of its lining in response to a continued gluten assault that the celiac doesn't absorb nutrients and thus becomes anemic or even more sick; and, (the one that really keeps me in line) untreated celiac disease is related to a higher risk of small bowel cancers (lymphomas) that have a poor prognosis.
And here's the real kicker today: a study found that one in 150 North Americans is a celiac. Further, because symptoms can be quite vague - fatigue, failure to grow, and so on - and because many doctors don't often think of celiac disease, celiacs often have the condition for (gulp!) 12 to 14 years before it's diagnosed. So if you have symptoms that have defied analysis, it's worth mentioning this possibility to your MD.
By the way, I wasn't diagnosed until my mid-twenties, and I've long been sure that if my parents had had me diagnosed earlier, I'd now be 6' 10" instead of 5' 6", although I must say that my 5' 2" dad and 5' 1" mom never agreed with me.