When you eat foods with a lot of sugar/carbs, your pancreas pumps out insulin to regulate blood-sugar... however, over time with the excess insulin, your cells will stop responding to the insulin and therefore become "resistant" to it. That becomes a huge problem, because insulin is needed to regulate your blood-sugar and if your cells are no longer accepting it, your blood-sugar gets very high..... this is how type 2 diabetes happens. It doesn't happen over night and being slightly insulin-resistant is fine, because you can always reverse it. I hope this explains it.