Is fructose bad for you?
It doesn't cause spikes in insulin and blood sugar, but large amounts of fructose may contribute to overeating.
Most of the sugar we eat gets broken down and absorbed in the small intestine. Swarms of specialized enzymes attack larger molecules and convert them into three simpler sugars: mainly glucose, but also galactose (a part of lactose, the sugar in milk) and fructose. There are a few more steps involved in breaking down the starches in bread, potatoes, and the like, but ultimately starch shares a similar digestive fate.
Our livers prudently stow away some of the absorbed glucose as glycogen, a molecule that can be turned back into glucose when we haven't eaten for a while. But most of the sugary stuff is distributed right away. Glucose levels in the blood shoot up, and the pancreas gets busy, pumping out the insulin that cells throughout the body need in order to take in glucose and use it for energy.