If they started using them without informed consent, was it a choice?

And even then, you do have a chemical dependancy on enough calories, that dependency led to an evolved response mechanism, that mechanism is exploited by junk food manufacturers. That the substances your body and brain produce in response to food stimuli are endogenous (made in your own body) rather than exogenous (made outside) doesn't make them magically less potent — some of us can get past this with our willpower*, but observationally it's obvious that most of us can't.

* I seem to have a lot of willpower, but I suspect that's mainly that my conscious self is fairly oblivious to my body's needs, as my willpower also leads to me pushing myself too hard in various different ways.