What are Cruciferous Vegetables?

Cruciferous-VegetablesCruciferous vegetables are of the family Brassicaceae, also known as Cruciferae, and include cauliflower, cabbage, garden cress, bok choy, broccoli, brussels sprouts and similar green leaf vegetables. Other examples include oriental cabbage, arugula, watercress, radish, daikon, wassabi, and various mustards.

Ten of the most common cruciferous vegetables are in the species Brassica oleracea, and are often referred to as cole crops. Cruciferous vegetables are one of the dominant food crops worldwide, are high in vitamin C and soluble fiber, and contain a wide variety of healthy nutrients and phytochemicals.

Selective breeding resulted in a large variety of vegetables being available. Common cruciferous vegetables include:

Cruciferous vegetables can potentially induce goiter formation, as they they contain enzymes that interfere with the formation of thyroid hormone in people with iodine deficiency. At high intake, they can inhibit the incorporation of iodine into thyroid hormone and also the transfer of iodine into milk by the mammary gland. Cooking for a minimum of 30 minutes reduces the amount of goitrogens and nitriles.

Cancer Prevention Benefits of Cruciferous Vegetables

Cruciferous plants contain a high concentration of glucosinolates. Glucosinolates are the precursors of isothiocyanates (mustard oils). Glucosinolates and their breakdown products isothiocyanates are well-known protectors against cancer, suggesting greater intakes may lower cancer risk.

Since the early 1960’s, both natural and synthetic isothiocyanates have attracted attention as effective protectors against chemical carcinogenesis. As an example, cigarette smoke releases carcinogenic compounds in the lungs. Lung tissue activates these compounds to carcinogenic compounds that cause carcinogenic changes. Isothicyanates isolated from vegetables were effective inhibitors of this activation by inhibiting enzymes that are responsible for this conversion. Isothiacyanates also increase the excretion of metabolic byproducts of the carcinogens.

Evidence of the preventive effects of crucifer consumption and cancer has been shown to exist among several types of cancer, including:

  • Bladder cancer
  • Prostate cancer
  • Breast cancer
  • Non-Hodgkin’s lymphoma

Cruciferous vegetables detoxify by upregulating detoxification enzymes, preventing oxidative cell and DNA damage, and are chemoprotective against numerous types of cancer.

Bladder Cancer

Almost 50,000 men in the Health Professionals Followup Study were studied during a 10 year period for the relationship between variables such as fruit and vegetable intake and bladder cancer. There were no significant associations found between bladder cancer and the consumption of:

  • Total fruits and vegetables
  • Fruits only
  • Vegetables only
  • Yellow vegetables
  • Or green leafy vegetables

There was, however, a 51% risk reduction for bladder cancer in those consuming 5 or more servings of cruciferous vegetables a week versus those consuming <1 serving a week.

Prostate Cancer

More than 1,000 men were studied for the relationship between fruit and vegetable consumption and the occurrence of prostate cancer. Findings showed men who consumed 28 or more servings of vegetables a week had 33% reduction in prostate cancer risk. Those consuming 3+ servings of cruciferous vegetables had a 41% reduced risk compared to those that consumed only 1 serving or less a week.

Selecting and Storing Cruciferous Vegetables

Cauliflower

Choose heads that are compact and white. They can be stored in the refrigerator for up to 5 days in a plastic bag or airtight container. Trim off brown or black spots before you use the cauliflower. Soak the cauliflower for 10-15 minutes in cold water, then add a teaspoon of vinegar and a teaspoon of salt to freshen the head. Peel the stems and trim the leaves to use in soups. Cauliflower may turn yellowish if cooked in hard or alkaline water. Add a teaspoon of lemon juice to the water and to keep it white.

Cabbage

Choose firm, compact heads with good color. Celery or Chinese cabbage should be firm and have good color in the crinkle-leaf tops. Store unwashed heads for up to 2 weeks in the refrigerator in a plastic bag. Remove damaged leaves and wash thoroughly. Don’t cut or shred the cabbage until right before you are getting reay to use, as exposing the cut surfaces to air can destroy vitamin C. The greener the leaves of the cabbage, the more vitamin C they have. Use as little water as possible when cooking to preserve nutrients.

Brussels Sprouts

Good brussels sprouts are firm, compact, and a green color. Avoid puffy, soft, or yellowing leaves. Sprouts are best used immediately after buying. You can store them for up to 4 days in an airtight container in the refrigerator, or even freeze them if you want to store them longer. Wash sprouts before cooking, then cut off the stems and remove any loose or discolored leaves.

Kohlrabi

Choose bulbs 3 inches or smaller in diameter and use them within a few days of buying. Peel only the base to preserve nutrients. Small leaves can be cooked like spinach. You can substitute raw kohlrabi for bamboo shoots.

Cooking and Smelling

Cabbage, Brussels sprouts, and cauliflower all contain sulfur compounds. The sulfur is released into the air when the vegetables are cooked resulting in an unpleasant smell. The longer you cook these vegetables, the more sulfur will be released. To reduce the sulfur smell:

  • Don’t overcook
  • Put a walnut still in the shell in the water

Cruciferous Vegetables, Iodine and Thyroid Function

Very high intake of cruciferous vegetables have been found to cause hypothyroidism in animals. Hypothyroidism is insufficient thyroid hormone. There an instance where an 88-year-old woman developed hypothyroidism and coma following consumption of an estimated 2 – 2.5 pounds of raw bok choy per day for several months.

The breakdown of some glucosinolates may produce goitrin, which can interfere with thyroid hormone production. Indole glucosinolates breakdown results in the release of thiocyanate ions, which competes with iodine for uptake by the thyroid gland. Increased exposure to thiocyanate ions from cruciferous vegetable consumption does not appear to increase the risk of hypothyroidism unless accompanied by iodine deficiency.

Beneficial Compounds in Cruciferous Vegetables

Vitamins

Minerals

Phytochemicals

Cruciferous Vegetables Nutrient Content

(100 calories worth of each vegetable)

BroccoliBrussels sproutsCabbageCollard greensKale
(chopped/steamed)(boiled)(shredded/boiled)(chopped/boiled)(chopped/boiled)
Vitamin A (IU)5178184060012,00826,455
Vitamin B1 (mg)0.200.280.270.160.19
Vitamin B2 (mg)0.410.200.240.400.25
Vitamin B3 (mg)2.131.561.272.201.51
Vitamin B5 (mg)1.80.640.640.830.17
Vitamin B6 (mg)0.500.460.520.480.50
Folic acid (mcg)2131549135748
Vitamin C (mg)2791599170147
Vitamin E (mg)1.702.180.703.372.58
Vitamin K(mcg)35135922114222921
Iron (mg)3.13.10.791.763.22
Magnesium (mg)8851366564
Manganese (mg)0.770.570.552.161.49
Phosphorous (mg)23414368100100
Potassium (mg)1146810439998815
Zinc (mg)1.410.510.421.620.72
Protein (g)10.66.54.69.56.8
Fiber (g)10.66.710.510.77.15
Omega-3 fatty acids (g)0.450.430.520.360.36

Cookbooks

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References

Kristal AR, Lampe JW. Brassica vegetables and prostate cancer risk: a review of the epidemiological evidence.

Liu RH. Potential synergy of phytochemicals in cancer prevention: mechanism of action.

van Poppel G, Verhoeven DT, Verhagen H, Goldbohm RA. Brassica vegetables and cancer prevention. Epidemiology and mechanisms.

Walters DG, Young PJ, Agus C, et al. Cruciferous vegetable consumption alters the metabolism of the dietary carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in humans.

Fenwick GR, Heaney RK, Mullin WJ. Glucosinolates and their breakdown products in food and food plants.

Chu M, Seltzer TF. Myxedema coma induced by ingestion of raw bok choy. N Engl J Med. 2010;362(20):1945-1946.

McMillan M, Spinks EA, Fenwick GR. Preliminary observations on the effect of dietary brussels sprouts on thyroid function.

National Cancer Institute. Eat a Variety of Fruits & Vegetables Every Day.

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