I hate to say it but high carb or high fat diet are unrealistic!!!!!!
Try grinding up 25g-50g of flax seeds in a coffee grinder and add them to a fruit/baby spinach smoothie in the morning for a week. See how you feel "mentally".
We humans require exogenous fatty acids whole plant foods to build the brain.
Please break away from the cult mentality and you'll see the benefits of consuming whole plant non-oxidized fatty acids.