When insulin resistance affects the brain, it is deleterious. It interferes with metabolism, promotes inflammation, and inhibits the cleanup process of proteins from the brain. So those proteins accumulate and cause toxicity.
If it's not the fat, then what is it? Protein has remained the same for several decades, so let's look at the next macro-nutrient group, carbohydrates. As we discussed previously, people starting eating less fat and more carbohydrates