Jerusalem artichoke root. It contains inulin, a close relative of insulin. It has to become a large part of the diet. It can help.
It's easy to grow. It grows like a weed and self replicates. Actually, it's quite invasive. It looks like a sun flower, but the flowers on the large stalks are smaller.
Anyone can eat this. A normal serving is a root about the size of an egg.
from Wikipedia;
Unlike most tubers, but in common with other members of the Asteraceae (including the artichoke), the tubers store the carbohydrate inulin (not to be confused with insulin)