It's well established science that chemical reactions, hormones, etc. in the body 100% influence your hunger and cravings.

That doesn't mean that it's not within the means of human willpower to overcome it - everyone has the power to not be obese. But that doesn't mean that it isn't significantly harder for some people based on their genetics, biochemistry, the feedback loop of being obese, etc.

Some people get out of opioid addictions cold turkey, by just not consuming more opioids, enduring the withdrawal symptoms, and then getting rid of the chemical dependency.

Since we know this phenomenon is real, this means that, even with a chemical dependency, people choose whether to take the drug or not. So, by your logic, they are not really addicted, they can just choose to stop at any time, they're just silly and weak people, right?

Of course this is reductive and simplistic. Ultimately your choices are a computation that your entire nervous system makes, and urges and cravings are a component of that, just like rational processes are. Different people's nervous systems weigh these factors differently, and have more or less powerful cravings and urges to begin with. It's absurd to think that your rational thinking can overwrite anything in any condition, and it's absurd to think that all people experience these thinks to the same extent.

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.

> chemical dependency from eating two cheeseburgers for dinner

Wouldn't the initial dependency be almost purely psychological for opioids as well? Most people certainly wouldn't develop a chemical dependency after just two doses as well.

> developed a chemical dependency which is no longer a choice.

Why? They still have a choice. Of course it might be much harder for them to stick with that choice than for someone suffering from a mainly psychological addiction.

> There is no such chemical dependency from eating two cheeseburgers for dinner instead of one.

Apparently not in your body, no. Or maybe you just failed to recognize what addiction is, and managed to overcome it. Good job!

Now stop trying to pretend that your lived experience equals everyone else's because it clearly doesn't.