Mangelwurzels were and still are grown as animal feed, as large roots, many rural museums contain a variety of large knives and hand cranked devices for chopping the large roots into cow and horse sized morsels. They are sometimes sown in late summer and grown as a fodder crop for sheep which graze the leaves off and fertilise the ground before cultivating and sowing a spring crop. Apparently humans can eat them both root and leaves when small. I would expect them to be high fibre. My mother never mentioned them as anything other than animal food and she grew up in rural Lincolnshire pre WWII. A slice of sugar beet was sometimes sucked/chewed as a sweet.
