Praise be to Allaah.
It is permissible to have
an operation to tie the stomach (i.e., making it smaller by putting a band
or staples) or to reduce its size and connect it to the small intestine for
the purpose of reducing excess weight, and this is not regarded as changing
the creation of Allaah, because it comes under the heading of medical
treatment. But that is subject to the condition that it be thought most
likely that no bad consequences or greater harm will result from that. One
should refer concerning that to a trustworthy doctor, because these
operations may have serious side-effects.
It is better to use dietary
methods, in consultation with specialists. If that does not succeed, then
you may resort to tying the stomach or re-channelling the food so long as
you are certain that it is free from harmful and negative side effects.
And Allaah knows best.