Bananas contain a protein called lectin, which is also found in many of the 'night shade' foods, such as potato, tomato and chilipepper, that some people with celiac or gluten intolerance have trouble with. Lectin is somewhat similar to gluten and can create an autoimmune response. This is due to the body confusing lectin with gluten. Some researchers even speculate that gluten sensitivity is actually a lectin allergy that was previously unknown. Yeah right, but suppose a gluten sensitivity is actually related to a latex allergy.
Bananas also contain a protein called chitinase that requires a specific enzyme to break down once it has been consumed. If this protein is not broken down it can cause severe abdominal pain and other gastrointestinal discomfort. Often if someone with Celiac Disease is not healed, meaning that their intestinal system is not in tact due to ingesting gluten, the enzyme needed to break down the protein can be lost.
In addition to the gastrointestinal symptoms some people experience flushing of skin, headaches, heart palpitations, rash on the skin, and numbness or tingling of the mouth. These symptoms can occur as quickly as moments after consuming food that contains lectin or chitinase or as much as a few hours. Just like lectin, chitinase can also trigger an autoimmune response, because the body sometimes mistakes it for a pathogen.
 Wagner: The latex-fruit syndrome in Biochemical Society Transactions - 2002