I was allowed to chew gum prior to surgery, then 2 weeks from my out from my surgical date I realized I may as well get used to NOT chewing anything so I did not have an added stressor during the liquid and soft phase of my post surgical diet. Not to mention not chewing any gum after surgery..
It is not recommended for those of use who have had RNY / Gastric bypass to chew gum due to air swallowing associated with gum chewing.
The air will fill your ouch and cause discomfort and take up space needed for your protein and foods. Ask Ralph / Dancing Bear about burping and space when eating...
I cannot speak for those who have had the sleeve or what their surgeons advise, I can only speak from my surgeons advice and my experience.