Bariatric surgery is associated with reduced incidence of clinical diabetes in obese participants without diabetes at baseline for up to 7 years after the procedure.

Using UK general practice data, over 2000 people who had undergone bariatric surgery were matched with controls and outcomes analysed over a 7 year period.

http://www.thelancet.com/journals/landia/article/PIIS2213-8587(14)70214-1/abstract
http://www.jwatch.org/fw109483/2014/11/03/more-evidence-bariatric-surgery-prevent-type-2-diabetes