If you define junk food as food which is low in nutritional value and relatively high in fat, sugar and salt, then the problem is satiety. Generally, such food is low satiety.
It doesn’t make you feel full, so you go on eating more, and consuming more calories, than if you had consumed something of equal calories, but high satiety.
I accept that not all food that people dismiss as junk food has low nutritional value, but the junk food which tends to be eaten as snacks rather than main meals often is.
Could someone tell me what happened to the post ...



