Nice job trying to insult me in your response, something which I didn't do to you. It shows a lot about your character when you can't have a discussion on nutrition without getting personal.

The conversion of carbs to fat is known as de novo lipogenesis. It is a very inefficient process and even though theoretically it is possible, realistically it is not because as you pointed out 9kg of potatoes a day is ALOT! Who do you know that just eats white rice, potatoes and fruit smoothies and gains weight from them?? My 400lb neighbor is not obese from KFC right he's obese from white rice lol. I can point at skinny Asian populations who were doing it for centuries. It's only now that the obesity and T2D rates in those populations are increasing as they add more fat and protein (in the form of animal products).