Fructose is distinct from all other carbohydrates in that it triggers a reduction in energy (ATP) in the cell, which is called the energy depletion pathway. The fall in energy (or ATP) causes a survival switch to be turned on, that activates a variety of processes to help the animal survive. This includes the stimulation of hunger, foraging, the storing of fat, and the development of insulin resistance. While this is meant to be protective, if a lot of fructose is metabolized, it can lead to behavioral disorders, obesity, diabetes and heart disease.
Image provided by, and used with permission of Andrew Brackins and Chris Magryta