Can duodenal ulcers and the stress that causes them cause great weight loss?

Dear Myname, 

Yes, one of the symptoms of duodenal ulcers is weight lose. 

See: 
Peptic Ulcer
<http://www.nlm.nih.gov/medlineplus/ency/article/000206.htm> 

Wikipedia - Peptic Ulcer
<http://en.wikipedia.org/wiki/Peptic_ulcer> 

I hope this answers your question. Please contact me if you need any
further clarification on this answer before you rate it.

I'd add a couple of quick comments on some issues not addressed in the answer...
Most importantly, the concept that emotional stress is a significant
cause of duodenal ulcers is somewhat out of date.  The two major risk
factors for duodenal ulcers are NSAID use (asprin, ibuprofen, etc) and
infection/colonization with H. pylori.  Environmental stress isn't
really considered a big factor.  Physiologic stress (i.e. severe
physical stress - surgery, cancer, shock, significant trauma, etc)
can, however, be associated with duodenal ulcers.
Check this link for a medical review of ulcers
http://www.emedicine.com/med/topic591.htm
Hope this helps out.
js