Gluten is a special type of protein that is commonly found in rye, wheat, and barley. That means breads, cereals, baked goods, and a lot of things you wouldn't even think of. The funniest one I've found? Veggie burgers. It was interesting that there is grain in a veggie burger patty, but I guess it makes sense - gluten has a binding and "chewy" effect in food.
Why is gluten a problem? Well, it can, in effect, act as a toxin in the human body:
"The nature of the toxicity, although to some extent stems directly from the chemical nature of gluten, is mostly due to a reaction that occurs by the immune system of individuals in possession of certain genes that recognize gluten for the foreign protein that it is and hence toxic. The immune system genes in control of this reaction are actually not rare, and may be present in up to 60% of Americans." (from finerhealth.com)60% of Americans! That's a majority! The symptoms of gluten sensitivity usually manifest in gastrointestinal discomfort (heartburn, nausea, indigestion, abdominal bloating and pain, and more). So, taking gluten out of the diet for 3 weeks gives us a chance to evaluate how our bodies feel without that "foreign protein" getting in the way.
Thanks to Wikipedia, wisegeek.com, and finerhealth.com for the info!
QUESTION FOR YOU: Wanna try no gluten for a few weeks? :-)