Is there any causal link between insulin resistance, Alzheimer's?

We have evidence that patients with insulin resistance at age 50 are about 30% more likely to develop Alzheimer's.

Because people with Alzheimer's may have developed insulin resistance later, the 30% number could greatly under represent the relationship, yet one can still have a hypothesis that these correlated facts relate to a common cause, or that Alzheimer's may have been instrumental in causing insulin resistance.

Is there any other plausible hypothesis?

While controlling sugar and carbohydrate intakes clearly contribute to avoiding insulin resistance, and lowering weight, via caloric restriction appears to cut insulin resistance, does restriction of fat intake, other than as it impedes weight loss, do much for controlling insulin production? If one is losing weight, even when most calories taken in are fat, my observation is that one still controls glucose levels and likely insulin production.

Contrary evidence?