In the Netherlands at the end of World War II, a five-month famine was the result of blockades by the German army. Rations dropped as low as 1600 kJ (400 calories) per day! This has enabled researchers to conduct long-term studies into the health effects of reduced nutrition, particularly in babies who were in utero during this period. A study at age 19 showed no cognitive differences, but a more recent study now that the people are in their fifties showed that those who suffered famine, particularly in the early stages of gestation, do show more decline than their non-famine-affected peers.
See Discover's 80 beats blog for a more in-depth analysis of the study.