I think the main reason we have growing levels of obesity (and the corollaries of that) is that we eat more and what we eat is more energy dense. Yes, other things have small effects, but basically we eat too much and do too little. For the extreme, take the average American portion size. Well, yeah, maybe there's a virus, maybe there's an effect from air pollution, etc. etc. but the main cause is too much food and too little exercise. FFS, I had a sandwich the other week that was so large I had to remove the majority of the filling just to fit it into my mouth. That's not normal. Washing it down with 16 fluid oz of sugar solution isn't normal. I had a BBQ platter at a restaurant in Nashville a while back, a meal so big that frankly I don't think I got through 20% of it before I threw in the napkin and admitted defeat.
Of course, this is where it gets complicated. The food industry loves all the conflicting advice, of course, those are product opportunities. Low fat becomes low carb, and have you tried our range of gluten-free drinks, and palaeo bars (it's important to keep up those energy levels when chasing a mammoth). They love food weirding. They're not out to sell broccoli (unless it's individually packaged, chocolate dipped, deep-fried Broccoli Bitez™) and that our relationship with food is broke. There's an entire industry that actively doesn't want you going home to chop up some veg and throw it in a pan.
