Fructose is mainly metabolized in the liver. The first step in
its metabolism is conversion to fructose-1-P by fructokinase.
Fructose-1-P can activate a signaling pathway that leads to
activation of a protein called JNK. This protein phosphorylates
another protein, IRS-1 at a serine residue, inhibiting it. Since
insulin signaling requires IRS-1 to work properly, congratulations!
Your liver is now insulin resistant. As a result, your pancreas
works harder to make up for it, producing more and more insulin.
This is fructose induced hyperinsulinemia. Eventually, your
pancreas won't be able to keep up and you will achieve Type 2
Diabetes Mellitus.
