When you overload a cart the horses take strain. Much the same with the human body. Each cell requires a few things : amino acids, glucose molecules, and a whole host of other complicated yet simple molecules.
Each cell in the body essentially respirates, breathes in so to speak glucose and oxygen and breathes out ATP and CO2 in order to function, much like the lungs and the opposite of what trees do.
Simple yet complex.
If you overload the system with glucose molecules they will simply be stored as fat for a rainy day and also overwhelm and flood the system with stickiness.
That is what diabetes is in the type 2 sense of the word, flooding the system and causing a sticky mess.
Type 1 however is an initial lack of the key that takes the glucose into the cell and forcing the cell to respirate anaerobically which leads to death without the rescue molecule insulin.
Starving in a sea of plenty is type 1.
Drowning in a sticky mess is type 2.
The ebb and flow of the cell works in harmony if the correct diet is maintained and goes horribly out of whack with an overload or under-dose of glucose molecule flow to the cell.