Gluten intolerance occurs when the body, specifically the digestive tract, responds to the presence of gluten in food. The response can range from mild discomfort to serious medical complications. Awareness is continuing to rise regarding the problems caused by gluten, even for people who do not suffer from a gluten allergy.
Why Does Gluten Affect People?
There are many potential reasons for an increase in gluten intolerance. Many researchers have focused their efforts on examining the role of diet and changes to one’s diet.
Consider for a moment, humans began eating cereals such as wheat, rye and barley (grains that contain gluten) within the last 10,000 years. A diet centered on these foods contrasts dramatically from the Paleolithic diet. The Paleolithic diet was the human diet for over hundreds of thousands of years. With this consideration in mind, many believe the human body may not be designed to digest components of these relatively new foods.
We also need to consider that many plants have defense mechanisms to discourage animals from eating them. They accomplish this by creating an immune response or disrupting digestion in the animal. What animal wants to eat a plant that causes intestinal discomfort or worse?
What are the Causes of Gluten Intolerance?
For some individuals, gluten intolerance occurs as celiac disease. For others, it is referred to as non-celiac, gluten sensitivity. Celiac disease is an innate allergy to gluten. For those with gluten sensitivity, the explanation has not been so clear.
Non-allergy induced responses in humans have been identified as either gluten sensitivity or a wheat allergy. Symptoms such as bloating, abdominal pain and diarrhea may result from an intestinal immune response.  Another factor may be reduced intestinal flora that result from gluten in the diet. Studies have found that individuals who consume a western diet have fewer ‘friendly’ intestinal flora colonies than those who consume a more primitive diet. 
Increased exposure to gluten may also aggravate an existing condition. Modern processing incorporates gluten into many foods where it does not naturally occur. Food manufacturers include gluten to increase the energy value of food, as well as flavor. This increased presence has been thought to increase the ability of gluten to aggravate the lining of the small intestine, creating digestive problems. 
Individuals who do not suffer from a gluten allergy may also experience gluten intolerance as a result of a change in the digestive tract. Gluten may cause an immune response and cause intestinal inflammation. It may also cause ‘unfriendly’ bacteria to colonize; leading to possible immune response, or simply a problem digesting normal foods.
Another possibility not explored has been the impact of GMOs (genetically modified organisms) on digestive health. While little research has been done on this subject, it bears consideration. Especially as reports of gluten sensitivity continue to rise right alongside the increased use of GMOs.