In "gas bloat syndrome", fundoplication can alter the mechanical ability of the stomach to eliminate swallowed air by belching, leading to an accumulation of gas in the stomach or small intestine. Data varies, but some degree of gas-bloat may occur in as many as 41% of Nissen patients, whereas the occurrence is less with patients undergoing partial anterior fundoplication. Gas bloat syndrome is usually self-limiting within 2 to 4 weeks, but in some it may persist. The offending gas may also come from dietary sources (especially carbonated beverages), or involuntary swallowing of air (aerophagia). If postoperative gas-bloat syndrome does not resolve with time, dietary restrictions, counselling regarding aerophagia, and correction – either by endoscopic balloon dilatation or repeat surgery to revise the Nissen fundoplication to a partial fundoplication – may be necessary.