You'd probably be surprised how much time I've spent learning about those subjects, from many different sources.

I'm an engineer. I want to understand stuff. Obesity is a perspective that I thin can give a ton of insight about human nature, society, evolution, progress, globalization, advertisement, medias, etc.

As for the definition, feel free to pull the definition from anywhere and see if there are any contradictions when applied to obese people.

http://www.asam.org/quality-practice/definition-of-addiction