It was explained to me by a Bariatric Surgeon at the Royal Bournemouth Hospital, (however I doubt there is any conclusive evidence in the form of studies I could point to as they predominantly concern themselves with the effects of additives and sweetners.) It is one of the reasons why Restrictive Bariatric patients are told not drink carbonated liquids after their surgery (lifetime). Like anything however, some people simply will never be affected by it, but if you think about it in its most basic premise, if you expand your stomach with gas then you will be able to get more food into it, particularly if you eat and drink at the same time and too quickly.
From a personal persepective, I feel the issue is more our dependence on carbohydrates, and the lack of education on the importance of low fat, protein rich diets, as you will be less likely to gain weight and be less hungry the greater the protein part of your diet is in relation to carbs. Everyone stresses about sugar, without realising that carbs are equally an issue in weight management.
