Similar to both cabbages and turnips, kohlrabi comes form the same cruciferous plant family. Because the bulb, which is he edible part of the plant, is not as rich in nutrients as the flowers and leaves, kohlrabi is not in the same nutritional league as broccoli, Brussels sprouts and kale. Still, it is a good source of vitamin C; a 1/2 cup serving provides 50% of the Recommended Daily Allowance (RDA). It also has about 200mg of potassium and a good amount of fiber.
The vegetable is high in flavonoids, plant pigments that work with vitamin C and other antioxidants to prevent cell damage that promotes cancer. Kohlrabi is also high in indoles, chemicals that reduce the effects of estrogen, and thus may reduce the risk of breast cancer. Isothiocyanates, another group of compounds in kohlrabi, promote the action of enzymes that may protect against colon cancer.
Kohlrabi should be harvested before it reaches full maturity; other wise, it becomes woody. It can be sliced and eaten raw, but it is usually steamed until tender. People who get gas after eating other cruciferous vegetables may have the same response to kohlrabi.