More recently, the research emphasis has switched from individual nutrients to diets as a whole. The role of the Mediterranean diet on cognition and dementia risk has been extensively studied. The Mediterranean diet is composed of a high amount of whole food, plant-based items; fruits and vegetables, cereals, monounsaturated fat in the form of olive oil, legumes as the main source of protein, nuts, moderate amounts of alcohol in the form of wine, and fish; low amounts of low-fat dairy products, meat and sweets.
Higher adherence to the Mediterranean diet is associated with a reduced risk of Alzheimer’s disease in multiple studies; the higher the adherence to the diet, the lower the risk of dementia. There are more than 20 publications on the internet regarding the effects of the Mediterranean diet on dementia and cognitive decline, and most of them show that in those who adhere to a Mediterranean diet, the risk of cognitive decline is much lower. The only clinical trial published in 2013 investigating the effect of this diet on cognitive health was performed on 522 people in Spain, who had a high risk for cardiovascular disease. The Mediterranean diet was supplemented with either extra-virgin olive oil or mixed nuts and was compared to a group consuming a low-fat diet control group. After six and a half years of intervention with the Mediterranean diet, people who ate such a Mediterranean diet had better cognitive performance than those who were on a low-fat diet. In a smaller subgroup of the same research, people who consumed more olive oil showed better results on a number of cognitive tests than those who used regular oil. Other Mediterranean Diet studies show that those adhering to the diet have less small vessel damage in the brain and also were less likely to advance from cognitive impairment to dementia compared to those on a conventional western diet. In fact in a recent study it was demonstrated that those on Mediterranean diet had less brain shrinkage than those on a regular diet.
Bottomline: There is plethora of evidence that a diet high in plant-based foods and mono-unsaturated fats as the main source of fat seems to prevent cognitive impairment.