Sudan: "nodding disease"
Check out this New York Times article:
About 300 children in and around this jungle village in southern Sudan have the mysterious ailment. It typically strikes during or just after a meal. The neurological disorder has left epidemiologists baffled. One of the few things understood about nodding is that it appears unique to southern Sudan.
Nodding is just one effect of the unusual malady. The children who begin nodding eventually stop growing when still small. Their brains stop developing as well, leaving victims mentally retarded. Eventually, the disease kills, and families dig tiny graves at the back of their mud huts.
... Researchers have found that the nodding occurs when children are fed the local diet of beans and starch. Candy bars, power bars and candy do not seem to have any effect.