The extent to which it happens can be just plain weird. In addition to what others have mentioned, it even seems to influence food choices made for others. Like the children of diet soda drinkers end up fatter than if the parent drank normal soda. There's also some 'very' preliminary suggestion that it screws with people's gut bacteria. Which in turn might lead to both digestive and behavioral issues.  It almost certainly has little impact if someone's calorie counting. But most people aren't.