<<Disclaimer:  Verify this information before applying it to your situation.>>

I am not a tax practiitioner, but My understanding is that the extra
expenses involved in adhereing to a medically prescribed diet is regarded
a tax deductible medical expense as defined and limited to those who
itemise deductions.  Like everything else you who need to keep careful
record of all extra expenses used to comply with the diet and have a note
from your doctor stating the necessity for the diet. This recommendation
may already be contained in the medical record letteres etc.  The celiac
disease foundation has a handout on it and similar sheets have been
reproduced in newsletters etc.  Obviously this may not apply outside the
USA.  Joe Murray