So it is normal to be underweight or overweight,
I wonder how normal it is. If a person had access to a lot of food, but it was all healthy food, would they be overweight? It takes a huge amount of eating healthy food to be overweight, but it doesn't take much unhealthy food to be overweight.
I don't think healthy food is the main reason for us becoming fat. Junk food and unhealthy food are the main reasons for becoming fat. When I was in 12th standard, I had a friend who was very fat and to lose weight he used to do a lot of exercise and even fasted but still he couldn't lose weight and instead gained weight.
That is my point. It isn't natural to be fat or thin. Thin can happen if ill, but very, very rarely can fat happen from illness. Fatness always comes from poor diet.