One of the foods that I choose to exclude from my diet are grains, primarily because they contain "anti-nutrients" which your body reacts negatively to when you consume them. The most well known of the grain anti-nutrients is gluten. Going gluten free has been pretty trendy lately, and there is a reason why - when people are cutting it out of their food choices generally people feel better. You don't have to be diagnosed with Celiac Disease to see that your body runs better when it's gluten free. Each person's gluten sensitivity varies, and some common health ailments that you have: headaches, allergies, stuffiness, bloating, etc could be related to gluten. The thing is that most people have been eating gluten since they were able to eat solid foods, so its difficult to know how much better you would feel without gluten until you cut it out. The chart shows 3 levels of gluten intolerance: sensitivity, wheat allergy, and celiac disease.
Gluten Sensitivity: Gluten sensitivity can manifest itself in the form of an "IBS-like stomach problems, headaches, fatigue, numbness and depression, but more than 100 symptoms have been loosely linked to gluten intake." Diagnosing gluten sensitivity is difficult, since there isn't a targeted set of symptoms, but "some experts think as many as 1 in 20 Americans may have some form of [gluten sensitivity]" so if you experience any of the issues listed above, it may be worth going gluten free to see if you feel better.
Wheat Allergy: If you have a wheat allergy it may be related to the gluten in wheat, but could be realted to something else. A wheat allergy is rare in adults and children, and most children that do have this allergy outgrow it by the age of 5.
Celiac Disease: The most extreme reaction to gluten is seen in the diagnosis of Celiac disease, once rarely diagnosed, is now estimated the "1 in 133 Americans" has celiac. Celiac is a condition where your body attacks gluten, can as a result creates chronic inflammation and can lead to malnutrition in extreme cases. To read more about celiac, gluten allergies, and gluten sensitivity read this article from the Wall Street Journal, Clues to Gluten Sensitivity .
The bottom line, many people are sensitive to gluten and although they are hard to diagnose, the symptoms that they experience are real and can be avoided by avoiding gluten.