Although they look very different, cabbage, kale, broccoli, kohlrabi, cauliflower and Brussels sprouts are all the same species of plant.  The differences between these plants are the results of thousands of years of human cultivation and selective propagation.

Kohlrabi is not a root vegetable, but rather a fleshy bulbous stem just above the ground.  There are both green and purple skinned types, and both have creamy white flesh.  Kohlrabi may look like a turnip, but its taste is very different, with a sweet, peppery, broccoli/cucumber flavour and crisp texture.  It is excellent raw by itself and in salads, and may also be steamed, stir fried, braised or stuffed.  The cooked leaves have a collard-like flavour.

Kohlrabi is high in fiber, an excellent source of Vitamin C and a good source of potassium.

• Uncooked cabbage is high in glutamine, an amino acid that is essential for intestinal health.
• Cabbages are a good source of Vitamin K, which is essential in the production of blood clotting proteins.
• Cabbage is high in potassium, which helps regulate blood pressure, promotes a steady heartbeat, and can lower your risk of stroke.
• Cabbage contains quercetin, an antioxidant that is a natural antihistamine that can benefit allergy sufferers.
• Savoy Cabbage is among the highest in beta-carotene.
• Bok Choy and Chinese Cabbage are highest in calcium.
• Red Cabbage provides the most Vitamin C.

A chemical (isothiocyanates) found in cabbages may lower the risk of lung cancer in smokers by as much as 38%
... although not smoking at all is best .