There is great advice here. I will gain weight eating 1000 calories a day from sugar and starch. My tolerance is basically nil. Your liver produces 300g of glucose for basic body functions everyday regardless of what you eat, so eating more carbs on top of that can be a recipe for disaster.
Fructose (half of the table sugar [sucrose] we consume is glucose, the other half is fructose) Is unique in the way it interacts in our body. Fructose crosses the blood/brain barrier, in a similar way to highly addictive drugs like opiates, cocaine, and methamphetamine.
The result is extreme cravings, withdrawal symptoms and very high relapse rates when trying to give it up. Many of the most addictive food products that people crave and can't give up are made with high fructose corn syrup, which is even more addictive than table sugar because of the higher fructose content.
I have read studies that report it is harder to quit sugar than smoking, heroin or alcohol addiction. The difference, of course, is that we recognize those are dangerous, deadly and addictive substances and have rehab programs set up to help those addicts.
Fructose is passed out by the fistfuls to children at Halloween, Christmas, Easter and readily available dirt cheap on literally every corner store and restaurant everywhere you look.