The journal Neurology reports that the proper diet seems to help prevent age-related brain shrinkage and cognitive decline.
From the press release:
People with diets high in several vitamins or in omega 3 fatty acids are less likely to have the brain shrinkage associated with Alzheimer’s disease than people whose diets are not high in those nutrients, according to a new study published in the December 28, 2011, online issue of Neurology, the medical journal of the American Academy of Neurology.
Those with diets high in omega 3 fatty acids and in vitamins C, D, E and the B vitamins also had higher scores on mental thinking tests than people with diets low in those nutrients. These omega 3 fatty acids and vitamin D are primarily found in fish. The B vitamins and antioxidants C and E are primarily found in fruits and vegetables.
So the dietary pattern linked to preservation of brain size and function in this study is: high omega-3 fatty acids and vitamins B, C, D, and E. I don’t know if study participants were getting these nutrients from supplements or from food or a combination. (I haven’t read the full article.)
To find foods high in the aforementioned nutrients, you can use NutritionData’s Nutrient Search Tool.
Note that the time-honored Mediterranean diet is also associated with lower rates of dementia and slower rate of age-related mental decline.
I previously reported that a supplement cocktail of three B vitamins slowed the rate of brain shrinkage.
Reference: Bowman, G.L., et al. Nutrient biomarker patterns, cognitive function, and MRI measures of brain aging. Neurology. doi: 10.1212/WNL.0b013e3182436598
h/t to Randall Parker at FuturePundit
Paleo Diabetic 
Advantages1. Strictly hunted and gterahed foodsOne of the main benefits of the diet is that it only included foods that humans could hunt and gather. Thus, foods such as grains and the majority of starches aren’t included in the Paleo Diet. Although it doesn’t include all available natural foods, it only includes natural foods. Cavemen didn’t spend their days hunting for frozen pepperoni pizzas, or gathering Twinkies.2. Lack of food byproductsFurthermore, the byproducts from various food sources, such as sugar from sugar cane, wouldn’t be allowed in a Paleo Diet. Many of these byproducts are unhealthy, and can create various unwanted results. This is particularly true of modern processed and prepackaged foods, which often contain a Frankensteinian list of man made ingredients.3. Weight lossThose who maintain a Paleo Diet can experience some benefits related to weight loss. Carbohydrates, which are a no-no in the Paleo Diet, include foods such as fruits, vegetables, grains, bread, pasta, and rice. By reducing the amount of insulin in your body, your body’s blood sugar level decreases. That allows your body to break down fat, instead of storing it. In a Paleo Diet, you essentially replace carbs with proteins.Disadvantages1. Unbalanced dietOne of the main criticisms of the Paleo Diet is that it includes a small sampling of food varieties. That means that people following the diet have a dietary deficiency of foods such as dietary fiber and carbohydrates. Clinical studies show that including grains and non-saturated oils in one’s diet tends to produce better overall results than the Paleo Diet does.2. High saturated fat consumptionAnother of the drawbacks of the Paleo Diet is that it tends to be high in saturated fat. That’s due to the high amount of protein that such diets are comprised of. This would actually be an asset for cavemen, who spent the majority of their day searching for food. But it can create a major problem in modern times, since we typically spend most of our days seated. In today’s world we spend more time hunting for information, than hunting for food.3. Totally new eating habitsWhile many of us have consumed healthy foods, most of us haven’t exclusively consumed cavemen’s foods. Thus, adjusting to the Paleo Diet can be somewhat challenging for many people.The Paleo Diet idolizes the diet of prehistoric humans, while undermining the value of a modern “well-balanced” diet. While some health experts fully support this diet, others believe that it’s simply a new fad diet with an old history.