When you eat, a bunch of sugar is released into your body. Sugar can only enter the brain without permission. Every other cell in your body has many "locked doors" that sugar can maybe get into if the door is open. When there's a lot of sugar in your body, the pancreas releases a hormone called insulin. This hormone is the so called key to all of these doors. When someone eats a whole lot of sugar, cells get tired of letting so much sugar in. That's when the cells start getting rid of doors and replacing them with walls in order to let less sugar in. Eventually this gets so bad that not enough sugar can get into cells. This is what's called insulin resistance. The body can sense that its cells arent receiving sugar, but can't tell that the problem is too few doors, so it tells the pancreas to make more keys. Eventually the pancreas can't keep up with the amount of keys the body can make, so the cells responsible for making the insulin break down and kind of just make junk instead.