Well as one of my former employees said; back in the 50s when you had one bottle of coca-cola (the glass bottle, 50cl) you would be full and not eat anymore. Because back then the sugar used was pure sugar, glucose. What this does is transform into glycogen and then when you need it because you are doing sport or in need of sugar, glycogen will transform back into glucose and be usable by your body.
Today, you have a 50cl bottle of coca and you want more... why? because instead of pure glucose, you have an artificially created glucose-fructose. What this does is that the glucose still transforms into glycogen but the fructose goes directly into fat. And since you have less glucose, your body doesn't feel as full as on sugar only. Plus, like in some brands of crisps (chips) they add this artificial product (can't remember the name) that creates a craving. So you want more however bad it is for you... I see it with my boyfriend. When he starts a pack of crisps, if I don't take it away from him, he'll eat it all... ...