I don't know what your purpose is for asking this question as academic research or personal change in nutrition... For answer, reduced caloric or intermittent diets, high carbohydrate/low protein diets, and even any kind of diet have positive or negative side effects that vary from person to person and from society to society. That is, different diets will have different results on a selected individual.

When we scan the literature, many studies show that many different types of diets increase or preserve life expectancy or cognitive abilities compared to other diets. However, this does not exactly show that one diet is better or worse than the other, but that it is more suitable for that person or society. Only poorly designed research will reveal problems.

The research you added is relatively old and little bit lack of research on humans but shows promising results in it. And the both nutrition styles you first mentioned can cause state of irritability and therefore cognitive differences in psychological terms at long-term(I can't say for sure whether they increase or decrease). Also, brain use only glucose and ketones as energy sources, which should also be taken into account in your question, as these are nutrition types that easily affect the amounts of these substances in the body thus cognitive abilities.

To summarize, as a dietitian, my advice to you is that nutrition is not the only factor affecting life expectancy or cognitive decline. And many nutrition styles have a positive effect on this topic compared to other diets. However, the main effect of nutrition style is seen when it is applied to an individual and each individual responds differently to each diet.