The four body shapes
A recently released study from Tufts University whose main campus is in Medford, Massachusetts showed that when people on a diet stopped eating carbohydrates (carbs) they did not do as well on tasks that used their memory as they did when they just ate fewer calories.
When the participants started to eat carbs again their memory skills came back. This was a very small study and most researchers would not call it a valid study. There were 19 women between the ages of 22 to 55. More research has to be done but this information albeit a small study clearly showed "that after a week of severe carbohydrate restriction, memory performance, particularly on difficult tasks, is impaired."