Why is sugar sooo addictive?

Sugar addiction. You can learn a lot from "sugar: the bitter truth, "; a 90 min vid on youtube by pediatric endocrinologist robert lustig of ucsf. He breaks it down so it is very understandable and also addresses the political and economic aspects of the marketing of sugar. Also, consider that sugar, caffeine, nicotine and amphetamines all have the same effect curve - a quick lift and then a "crash.".