Sugar is fattening, primarily due to its high content of Fructose
Fructose produces glycotoxins which are pathogenic compounds resulting in conditions like diabetes.
Fructose does not suppress Ghrelin , which is the "hunger hormone".
Fructose does not stimulate insulin and leptin. Insulin helps the body assimilate sugar and leptin is the hormone that signals satiety.
Since leptin is not stimulated and Ghrelin is not suppressed, the brain thinks we need to eat more, which causes the person to eat more fructose, which in turn causes leptin to be suppressed even more.
This results in the VICIOUS cycle which results in sugar addiction.
Fructose can only be processed by the liver, just like alcohol.
A person addicted to SUGAR craves sugar everyday.
This finally ends in OBESITY.