[SketchySeaBeast]

You didn't address their point that zoo animals have to sometimes be kept on diets to remain slim, in spite of their all natural diet. This article seems to think it's a whole gamut of things that keeps these animals thin. http://sciencenordic.com/can-wild-animals-become-overweight

Appetite and satiation are far more complex than just "eat until your full and then stop", for instance amensiac patients have been observed to eat waaay more than they should have just because they did remember eating (Rozin et al. (1998)), even they should have by all rights been physically full. There's whole layers of cognitive, emotional, and behavioral patterns with excess food consumption.

Personally, I have been able to effectively lose and keep off weight while still enjoying all manner of unnatural foods (Ice cream, McDonald's and candy, oh my).

[Terr_]

I had success with calorie-counting, and I think part of that came from accidentally co-opting an existing behavior involving bargain-hunting and frugality.

Food choices became about avoiding "spending" my calories on "bad deals", avoiding foods which didn't promise enjoyment commensurate to their cost.

[SketchySeaBeast]

I did that too - I made sure to get my protein (via protein shakes), but after that just ate what I wanted. I developed the same habit too - I ended up restricting things like rice or pasta because I'd rather "spend" those calories on an ice cream cone.