text: my child has been diag.with ibs and is lactose intolerant. what about fast food what can he eat mcd's bk etc   there is nothing wrong in letting your child eat mcdonalds on occassion. let your child be a child as far as stuff like this goes. my son has ibs and that is why antidepressants didnt work for him as ibs is linked to the lack of a certain enyme in the gut that regulates the serretonin in the brain. just with diet alone we have almost eliminated his outbursts. no more medication for my son! lactose intolerent was a problem for my son in the beginning. we tried otc chewables for a while. that seems to reverse his type of ibs into constipation type ibs. i would take him off the enzymes for the ibs and just watch his diet. but please at least once a week, if its mcdonalds or a small bag of skittles, let him indulge.