Food is much more complex than fiber vs. calories. I am not a scientist there but I observe myself and others a lot. When I eat certain foods I can eat a lot without weight gain, my digestions works, my mind works, I go to the bathroom regularly. When I eat junk food, I gain weight, I feel sluggish and I often get constipated. Unless I am very special, which I don't think I am, I assume other people experience the same thing.
