The fat person on a high carbohydrate diet is nearly starving in the midst of plenty. Most of the carbohydrate absorbed is turned into fat and accumulates in fat stores and he cannot easily get it out again. The rest of the tissues of the body suffer a relative deprivation of nutriment and naturally he feels hungry and eats more.
Habit, reinforced by the cheap price and ready availability of starchy and sugary foods, ensures that attempts to satisfy the hunger with yet more carbohydrate which in turn forms more fat and still leaves them hungry. The vicious circle goes on and you get fatter. People have exchanged the traditional high fat, high protein, low carbohydrate diet with a low fat, low protein, high carbohydrate diet. That is, we have replaced bacon and eggs with cereal, and meat and two vegetables with pizza. And this has been accompanied by a general increase in obesity.
Of course this is perfectly obvious. A person can't get fat unless he/she eats more food than he/she uses up for energy. But it is beside the point.
