The juxtaposition of these two food pyramids says a whole lot– the first one illustrating a modified paleolithic way of eating (there may be several versions of this), and the second one illustrating the current USDA recommendations.  The two most obvious differences are (1) the carbohydrate and grain percentages of the diets, and (2) the paucity of healthy, natural fats and oils in the current Standard American Diet.  Our genes, which code for how foods communicate with our hormones and immune system, have co-evolved for thousands of years with the first pyramid’s depiction of food.  The rapid shift in how we eat that has occurred post-industrialization has not allowed adequate time for our bodies to appropriately adjust.
There is an increasing amount of research looking at the effects of a high sugar, high carbohydrate diet on brain function and cognition.  Alzheimer’s Disease is now referred to as “Type III Diabetes,” because of the damaging effects of impaired glucose uptake and the inflammatory chemicals associated with high insulin states.  Below are a few articles on the effects of sustained elevations of insulin on the brain.  Not only is glucose uptake impaired, but neurotoxicity and inflammation occur from microglial activation (these cells are the “Keepers of the Brain”).  Coupled with a Standard American Diet that is low in healthy, natural fats, neuronal function is greatly compromised.  The hippocampus (memory center) is particularly vulnerable to changes in glucose metabolism.

There is currently no cure for Alzheimer’s Disease, and other neurodegenerative conditions are on the rise as well.  The best way to keep your nervous system cells healthy is through prevention, by shifting your food choices to those containing less insulin-stimulating sugars and carbohydrates.  Second is to make sure your diet is sufficient in healthy, natural fats– fish and fish oil, olive oil, avocados, eggs, coconut oil, ghee, butter from pastured cows, etc.  Most people don’t need to go to the extremes of very low carb diets like strict Paleo or Atkins or ketogenic diets, but making a deliberate shift in proportions by using the food pyramid guides would be a good first step towards brain and overall wellness.  Prevention is the best medicine.