To adress that last comment, it's true. I am definitely not allergic to gluten. Food allergies are not the same thing as food intolerance. An allergy is when your immune system essentially overreacts to a foreign (but normally benign) substance. Your basophils (a type of white blood cell) release histamines, which cause any number of reactions, including hives, sneezing, runny nose, red, watery eyes, and in the worst cases, anaphylactic shock. A food allergy isn't all that different from a pollin allergy. I know people who sneeze when they eat bread because of a wheat allergy, or who get rashes on their arms when they eat gluten. Of course, we all know about the people who swell up and die when they eat peanuts. Allergies can be tested somewhat reliably, so people are far more receptive to the existence of allergies than intolerances.
Food intolerance is a tricky beast. A food intolerance is when the body reacts poorly to a certain food, or when they body can't properly process a certain food. The symptoms of food intolerance may seem completely unrelated to the digestive system, but they can be determined by eliminating a certain food or group of foods from the diet. If the symptoms go away when you stop eating the food for an extended period, and they come back when you reintroduce it, then it's a good sign that you have a food intolerance. Some common symptoms of food intolerance are gas, bloating, migraines and other head aches, fatigue, weakness, and systemic (meaning system-wide, or body-wide) inflammation, which can cause muscle pain, and nerve problems. Some people even have emotional reactions to foods, including sadness, irritability, and anger. People can be intolerant to just about any food, although gluten and dairy are the most common. People can be intolerant to nightshades (including tomatos, peppers, potatoes and eggplant), soy, and corn, among others.
The first time I ate gluten after I'd been gluten free for a while, I had a strange stomach ache (it was neither indigestion nor nausea), a headache, mental fogginess (i.e. the inability to think clearly), and extreme fatigue. My ulnar neuropathy, which hadn't caused me problems in years, came back in full force, my low back pain flared up, and my symptoms of gastritis came back after being gone for months. When I'm gluten free, my ulnar neuropathy doesn't flare, my low back pain is almost nil, and my gastritis is a thing of the past. Although I definitely miss some of the wonderful gluten-full foods out there, my desire to feel good far outweighs my desire to eat a donut.
I also want to clear up the confusion that people have about Celiac disease and gluten intolerance. Celiac disease is an auto-immune disorder which causes the cilia of the small intestine to be damaged when gluten is ingested. If these are damaged, it makes it difficult for the body to absorb vital nutrients. It is a very serious condition which may be asymptomatic, or it may have any number of symptoms, including gas, bloating, fatigue, mineral and vitamin deficiencies (such as calcium, iron, and B12), a large appetite with no weight gain, or unexplained weight gain, to name a few. It is common for people with Celiac to be extremely sensitive to gluten, to the point where they may not be able to tolerate food prepared in a kitchen where foods containing gluten have been prepared. It is also common for them to have a reaction to gluten that lasts for 3 days (the amount of time it takes for gluten to leave the body). People who are gluten intolerant may have Celiac disease, but they may not. The only way to know for sure is to be tested after eating gluten for 4 weeks (something I'm not too keen on doing, given how gluten makes me feel. I can't think of any time in my life when being fatigued, brain dead, and in pain for a month will be convenient). If someone tests negative for Celiac disease, it does not mean that they don't have a gluten intolerance; it just means that they don't have Celiac.
For those of you who may still be skeptical, I'll leave you with this. Even if an intolerance is "all in someone's head" (which, odds are, it's not), if they feel better when they don't eat something, then their choice not to eat it should be respected. Most people who have special dietary needs are pretty understanding that their food requirements can be a giant pain in the ass to those who can eat anything. I am always prepared to bring my own food to parties or dinners (and if you ask nicely, I'll even bring enough to share), and I never expect people to accomodate my diet, though it's always a pleasant surprise when they do. If I ask what's on the menu, or if I read a label, it's not because I'm picky or trying to be disrespectful; I just want to make sure I'm not going to be miserable (and in the case of dairy, I get so gassy that really, it's more disrespectful of me not to read labels!). I don't bitch and whine when I can't eat something (well, usually), and I don't begrudge others their right to eat whatever they hell they want. A little empathy can go a long way. After all, it sucks to not be able to partake in a freshly baked loaf of bread or the pizza that everyone else is eating. And by the way, if I could choose to make my gluten problem go away, you can bet everything you have that I would do it in a heartbeat.
http://www.celiac.org/