The Sunday Times have been a doing a GI diet supplement for a couple of weeks. They produce a booklet which lists common foods in red, amber or green based on their Glucose Index Value. In the green section on breads they have a bread called Pumpernickel, a dark rye bread.
Here follows the etymology of the word:
The true origin of "pumpernickel" is nearly as strange, if somewhat less savory. "Pumpern" was a New High German word similar in meaning to the English "fart" (so chosen because, like the word "achoo," it imitated the sound it described), and "Nickel" was a form of the name Nicholas, an appellation commonly associated with a goblin or devil (e.g., "Old Nick" is a familiar name for Satan). Hence, pumpernickel is the "devil's fart," allegedly a reference to the bread's indigestible qualities and hence the effect it produced on those who consumed it
http://www.straightdope.com/mailbag/mpumpernickel.html