Why do insulin injections treat type II diabetes?!

What you're describing is known as insulin resistance. Insulin resistance doesn't stop the cells from using insulin entirely. In fact, a person in the early stages of insulin resistance can maintain normal blood sugar because the pancreas responds by producing more insulin. Insulin resistance simply makes it more difficult for insulin--injected or natural--to work effectively. If an insulin-resistant person injects enough insulin, eventually blood sugar will go down. People with insulin resistance do typically have to inject more than an insulin-sensitive Type 1 diabetic.

Also, over time, many insulin-resistant Type 2s become insulin deficient. The beta cells in the pancreas die and do not get regenerated, so the pancreas loses some of its insulin-producing capacity. At this point, eating a low-carbohydrate diet, exercising, and taking oral medications that either improve insulin sensitivity or stimulate the pancreas to make more insulin won't work, and injected insulin is the only answer. There's some evidence that by the time a Type 2 is diagnosed, over 50% of his beta cells are lost, meaning that the problem is no longer just insulin resistance.

It seems that for some Type 2 diabetes, extra insulin helps persuade the body tissues to burn up a little more glucose. Insulin isn't considered a 'drug' since the body manufactures it itself. I'm on a diabetic mailing list and I read that many type 2s use insulin. They usually try it in desperation, after various other meds don't work for them, but most of them say they wish they'd tried it sooner.

BTW, did you know your name is related to diabetes? The full name is 'diabetes mellitus', and the mellitus comes from the same root as Melissa. From the Greek word 'mel' which means -honey-. Melissa means 'sweet like honey' (and I bet you are!) 'Mellitus' comes from the old days when they used to diagnose diabetes by tasting the person's urine! 8^P In uncontrolled diabetes, it's sweet like honey!

The insulin injections are not a treatment for the insulin resistance. They are simply to help lower blood glucose levels, something which it can't do by itself anymore. Otherwise, the patient would suffer the debilitating consequences of elevated blood sugars.

From a management point of view, this of course is greatly helped by eating low-carb so that the body needs less insulin. 'Less' is of course relative - an insulin resistant person will always need more insulin to metabolize the same amount of glucose as an insulin-sensitive person.

The body has many ways of raising blood glucose by itself, in the absence of food. But there is only one way of lowering blood glucose and that is insulin.