As the (real) title says, they think it is linked to ghrelin, a neuropeptide associated with hunger. Drinking something carbonated causes more ghrelin release

As the (real) title says, they think it is linked to ghrelin, a neuropeptide associated with hunger. Drinking something carbonated causes more ghrelin release (or less suppression of ghrelin released, actually) than drinking a still beverage. More circulating ghrelin leads to more hunger, which leads to more eating, which leads to weight gain. The mechanism that allows CO2 to act on ghrelin isn't really clear. They suggest that the bubbles push on the stomach wall, which in turn increases ghrelin release. The whole ghrelin pathway isn't known, but I thought pressure on the stomach walls would suppress, rather than induce ghrelin. There are a few other odd things too. For the rat experiment, they show weight gain curves (weight vs. time) for four groups: rats drinking a) water b) sugar soda c) degassed sugar soda d) diet soda. As you might expect, rats drinking water end up weighing the least, rats drinking (sugar) soda weigh the most. However, the rats drinking the degassed (sugar) soda weigh significantly less than those receiving diet carbonated soda. They take this as support for their theory, but it seems odd that this effect would totally dominate the actual calories in the sugary soda. Similarly, the carbonated (sugar) soda vs. carbonated (diet) soda groups also aren't different.