“Type 3 diabetes” is a term that has been proposed to describe the hypothesis that Alzheimer's Disease, which is a major cause/other forms of Dementia. It is triggered by a type of insulin resistance and insulin-like growth factor dysfunction that occurs specifically in the brain.
Here is a video by Dr. Neal Barnard, President of Physician's Committee, USA on Power foods for the brain.
Please watch the complete 17 minute video. It's very informative and educative. It is quite an emotional video, as he talks about his father who passed away from Alzheimer Disease...which perhaps made him to do the research as to how to prevent the disease.
Disclaimer: This is for information & education purpose. It can not be taken as a medical advice if someone is already facing memory loss. Please consult your medical practitioner.