Elevated blood sugar levels lower brain function in diabetics.  The effects of diet on your blood glucose levels can diminish memory and other cognitive skills.
D003072:Cognition Disorders / Q000097:blood / Q000209:etiology*; D048909:Diabetes Complications / Q000097:blood*; D006801:Humans; D006943:Hyperglycemia / Q000150:complications*; D008569:Memory Disorders / Q000097:blood / Q000209:etiology*