I've never had that happen - if it was going to happen to anyone, it should happen to vegetarians who go through tons of lettuce <img src="/images/graemlins/smile.gif" alt="" />
Iceberg lettuce (and most other common lettuces) really doesn't have much nutrient content - it's like eating plastic <img src="/images/graemlins/smile.gif" alt="" /> So I might instead try spinach - it might taste better to you, and give you far more nutrients per bite.
I know once I got scallops that were sandy, and it turned me off of scallops for over a year. So I understand how that can happen!