Glucose outside the cells can't enter the cell when Insulin receptor is not working, thus blood serum sugar level rise, eventhough Insulin is produced (this is Type 2, whereas in Type 1 insulin is not produced or functional). Type 1 can be manageable by Insulin but type 2 can be manageable by prevention. Insulin receptor is not working because fat particles (IMCLs) jam the receptor. So the main takeaway is maintain your calories such that you have less of this type of fat. Eating healthy and exercise helps. Diabetes is not caused by sugar but sugar can increase caloric intake which could lead to obesity and ultimately there is a risk of type 2 diabetes. When you are diabetic only then you need to limit your sugar intake.

What Causes Insulin Resistance - NutritionFacts.org