What Happens When You Cook Kohlrabi?

Nutritional Profile

  • Energy value (calories per serving): Low
  • Protein: High
  • Fat: Low Saturated fat: Low Cholesterol: None
  • Carbohydrates: High
  • Fiber: High
  • Sodium: Low
  • Major vitamin contribution: B vitamins, vitamin C
  • Major mineral contribution: Calcium, iron, phosphorus

About the Nutrients in This Food

Kohlrabi (“cabbage-turnip”) is a cruciferous vegetable, a thick bulb-like stem belonging to the cabbage family. It is high in dietary fiber, especially the insoluble cellulose and lignin found in stems, leaves, roots, seeds and peel. Kohlrabi is an excellent source of vitamin C and potassium, with small amounts of iron.

One-half cup cooked, sliced Kohlrabi has 0.9 g dietary fiber, 45 mg vitamin C (60 percent of the RDA for a woman, 50 percent of the RDA for a man), and 0.3 mg iron (2 percent of the RDA for a woman, 4 percent of the RDA for a man).

The Most Nutritious Way to Serve This Food

Steamed just until tender, to protect the vitamin C.

Diets That May Restrict or Exclude This Food

  • Antiflatulence diet
  • Low-fiber, low-residue diet

Buying This Food

Look for: Small vegetables with fresh-looking green leaves on top.

Avoid: Very mature kohlrabi. The older the stem, the more cellulose and lignin it contains. Very old kohlrabi may have so much fiber that it is inedible.

Storing This Food

Cut off the green tops. Then, store kohlrabi in a cold, humid place (a root cellar or the refrig- erator) to keep it from drying out.

Save and refrigerate the kohlrabi’s green leaves. They can be cooked and eaten like spinach.

When You Are Ready to Cook This Food

Wash the kohlrabi under running water, using a vegetable brush to remove dirt and debris. Then peel the root and slice or quarter it for cooking.

What Happens When You Cook This Food

Cooking softens kohlrabi by dissolving its soluble food fibers. Like other cruciferous veg- etables, kohlrabi contains natural sulfur compounds that break down into a variety of smelly chemicals (including hydrogen sulfide and ammonia) when the vegetables are heated. Kohl- rabi is nowhere near as smelly as some of the other crucifers, but this production of smelly compounds is intensified by long cooking or by cooking the vegetable in an aluminum pot. Adding a slice of bread to the cooking water may lessen the odor; keeping a lid on the pot will stop the smelly molecules from floating off into the air.

Medical Uses and/or Benefits

Protection against certain cancers. Naturally occurring chemicals (indoles, isothiocyanates, glucosinolates, dithiolethiones, and phenols) in kohlrabi, cauliflower, Brussels sprouts, broc- coli, cabbage, and other cruciferous vegetables appear to reduce the risk of some cancers, perhaps by preventing the formation of carcinogens in your body or by blocking cancer- causing substances from reaching or reacting with sensitive body tissues or by inhibiting the transformation of healthy cells to malignant ones.

All cruciferous vegetables contain sulforaphane, a member of a family of chemicals known as isothiocyanates. In experiments with laboratory rats, sulforaphane appears to increase the body’s production of phase-2 enzymes, naturally occurring substances that inacti-

vate and help eliminate carcinogens. At the Johns Hopkins University in Baltimore, Maryland, 69 percent of the rats injected with a chemical known to cause mammary cancer developed tumors vs. only 26 percent of the rats given the carcinogenic chemical plus sulforaphane.

In 1997, Johns Hopkins researchers discovered that broccoli seeds and three-day-old broccoli sprouts contain a compound converted to sulforaphane when the seed and sprout cells are crushed. Five grams of three-day-old broccoli sprouts contain as much sulforaphane as 150 grams of mature broccoli. The sulforaphane levels in other cruciferous vegetables have not yet been calculated.

Adverse Effects Associated with This Food

Enlarged thyroid gland (goiter). Cruciferous vegetables, including kohlrabi, contain goitrin, thiocyanate, and isothiocyanate. These chemicals, known collectively as goitrogens, inhibit the formation of thyroid hormones and cause the thyroid to enlarge in an attempt to pro- duce more. Goitrogens are not hazardous for healthy people who eat moderate amounts of cruciferous vegetables, but they may pose problems for people who have a thyroid condition or are taking thyroid medication.

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