The secret is lots of veggies, fruits, and whole grains. The calorie density is low so it's easy to stay in a normal calorie range or even a deficit which is key for reducing risk of type 2 diabetes. Fat, especially Saturated fat causes insulin resistance. Many studied show this. Please show me any long term studies or a culture that are metabolically healthy on long term keto diets. Take a look at Virta health. Tons of money spent on low carb diets that achieved very little.

Try a book like "fiber fueled". That's a diet that is actually sustainable.