I am not aware of a specific disease that links a food reaction with anal itching.
Testing the stool for parasites can be considered. Also, looking at the anal area to rule out pinworms should also be done.
Malabsorption can be evaluated by sending the stool off for fat analysis, as well as blood tests looking for celiac disease. Various breath tests can be done to look for bacterial overgrowth or lactose intolerance - all which can contribute to your symptoms.
These options can be discussed with your personal physician, or in conjunction with a GI physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
kevinmd_