You bring up a point which is not often given it's due in terms of rational discussions, and it involves "freedom", or more precisely free will and does it exist in any meaningful contextual sense. I think that is far more limited than many might and that obesity, "garbage" and the like are more symptomatic than causative of our problems. You may know that this isn't a conspiracy, but a fact that fast food and adverts are designed to bypass the rational part of the brain and trip the more primitive parts of the brain that we cannot control. McDonald's burgers as an example are designed to trip every addictive neurochemical mechanism possible and it's not a matter of chance but design. For all our pretense at being better than our ancestors, we are not. We are the Neolithic hunter-gatherer designed to live like the people on "Alone" in our only evolutionary mandates involve shelter, food, and sex and always on the verge of famine- always.
I think that obesity, diabetes, strokes, and more are co-morbidities more than anything else whose causal origins are related to brain chemistry that are both coincident and willfully created to a larger subject.
I can as you likely know bring on significant weight gain in most individuals without any dietary changes, increase the risk of diabetes, heart disease, hypertension, insulin resistance and more. All I need to do is create a situation of chronic sleep deprivation. Who today has good sleep hygiene and consistent amounts of it?
As you say it's extremely complex and poorly understood in anything remotely approaching proper context. My potential solutions for understanding are unconventional as I am of the opinion that this is beyond the direct abilities of our unaided biological selves.