I doubt this is a real concern. While normally I respect Dr. Cywes, I suspect he’s being going off the deep end, lately.
There is a normal phenomenon, when we eat a lot of carbohydrate, that the pancreas stores a supply of insulin intended to be released as the first phase of its response to a load of glucose (carbohydrate). On a carnivore diet, and even on a ketogenic diet, this first phase response is not necessary, so the pancreas stops storing extra insulin.
When a carnivore or a ketonian body is confronted with a sudden load of glucose, the lack of a first-phase response makes it falsely appear that the person is insulin-resistant on an oral glucose tolerance test. I suspect that this is what Dr. Cywes is talking about. But it’s perfectly normal, and perfectly healthy. There is no need for the first-phase response when we eat in a way that doesn’t require it.
Insulin is essential to life. If you are walking around, eating well, and staying healthy on a normal amount of food, then your pancreas is producing enough insulin. It’s producing a lot less insulin than it was back in your carb-burning days, but this is a normal, healthy, good thing. It’s not going to “forget” how to produce insulin, since insulin is essential for life.
If, on the other hand, you find yourself losing weight no matter how much you eat, you are thirsty all the time, and your urine smells sweet, then you should get checked for Type I diabetes. But Type I is an autoimmune disease. It’s been with us since the dawn of history (whereas Type II was barely known before the middle of the 19th century), and it is not caused by diet.