You may have an issue with the processed breading on the filet. Because of Fructose Malabsorption, I can't eat anything breaded from a fast food restaurant.
From a random website:
"Protein-rich fish, poultry and red meat are fructose and sucrose free. Marinated, seasoned or breaded meats, poultry and fish, however, often contain forms of fructose or sucrose. Avoid bacon, hot dogs, sausages and cold cuts, which typically contain variations of fructose, such as honey, high-fructose corn syrup or agave syrup, or forms of sucrose, including glucose, dextrose or sugar. Read product labels to ensure that packaged foods are fructose and sucrose free."
They're now wondering if it's not gluten, but the fructose in grains that give people problems.