April 20, 2014
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Leafy greens and other cruciferous vegetables

We have all been told by our mothers, doctors, teachers, and other sages of healthy living always to remember to eat our vegetables, particularly those that are green and leafy. The evidence is overwhelming that these delicious and beneficial greens contribute to a well-balanced and nutritious diet, especially those that belong to the cruciferous or cabbage family of vegetables. These are the vegetables, also called brassica vegetables, whose four-petal flowers form the shape of a cross - cruciferous means "cross-bearing." While the terminology may be new, these vegetables may already be a staple in your diet.

Cruciferous vegetables include Swiss chard, broccoli, cabbage, Brussels sprouts, cauliflower, watercress, radish, rapini, arugula, spinach, turnip, kale, and bok choy. Packed with vitamins and minerals (some crucifers have more than others), these vegetables boast impressive nutritional qualities and potent anticancer properties.

Nutrition experts often refer to brassica vegetables as "functional foods." Functional foods are foods that have benefits beyond basic nutrition - for instance, health benefits such as preventing certain diseases. Like all vegetables, crucifers possess high levels of antioxidants, including vitamin C, vitamin A, calcium, iron, folate, soluble fibre, and lignans. All these compounds may help reduce the risk of cardiovascular disease, since studies show that crucifers reduce plasma homocysteine levels, and higher homocysteine levels increase the risk for heart disease. Additionally, because of the high amount of calcium found in crucifers (especially kale, Chinese cabbage, and broccoli), they protect bone density and may help prevent the onset of osteoporosis, particularly in women.

Most findings on crucifers support their cancer-fighting abilities. Researchers have isolated sulfur-containing phytochemicals called glucosinolates that are abundant in cruciferous vegetables and that have the potential to inhibit cancer. These glucosinolates, when chopped, chewed, and digested, are converted into compounds called isothiocyanates, which act to prevent normal cells from becoming cancerous cells by stimulating the body to clear potential cancer-causing agents (carcinogens). Researchers from Ohio State University have shown that isothiocyanates are able to stop cancer cells from spreading. A 2004 study published in the Journal of Nutrition found that the isothiocyanate sulforaphane fights the spread of breast cancer cells, even in the later stages.

Isothiocyanates can also help prevent cancer. Some glucosinolates that cruciferous vegetables have in abundance have been linked to reducing the risk of breast, prostate, cervical, colon, and other cancers.

  • A Harvard and Ohio State study that showed that men who ate 2 or more half-cup servings of broccoli per week were 44% less likely to develop bladder cancer than men who ate less than one serving a week.
  • A study by the UCLA Medical Center found that people who ate more broccoli (about 4 half-cup servings per week) were 50% less likely to develop colorectal cancer than those who never ate broccoli.
  • Sulforaphane has been found to increase the liver's ability to help prevent cell mutations that may develop into cancer.
  • Researchers have found that one glucosinolate, indole-3-carbinol (I3C), deactivates an estrogen metabolite that promotes tumour growth, particularly in breast cells.
  • Other research found that men aged between 40 and 64 who ate 3 or more half-cup servings of cruciferous vegetables a week were 41% less likely to develop prostate cancer than those who did not.

Before you gorge yourself on crucifers, however, there are some cautions to heed. While they are loaded with beneficial nutrients, it should be noted that cruciferous vegetables also contain goitrogens and nitriles. In large quantities, goitrogens can reduce thyroid activity. Very high quantities of nitriles, which are found especially in Brussels sprouts, can have negative effects on the liver and kidneys. One way to lower the levels of goitrogens and nitriles in cruciferous vegetables is to cook them for 30 minutes or more. This will reduce the amount of goitrogens to one tenth and will also reduce a large amount of the nitriles. While cooking reduces the amount of nutrients in vegetables, it actually increases the amount of antioxidants absorbed by the body in crucifers.

In any case, the many benefits of crucifers far outweigh the small negatives. Not only are they cancer fighters, they also help control the appetite due to their high soluble fibre content, and they are thought to decrease the absorption of fats from other foods eaten during the same meal.

The next time you're planning a meal, reach for cruciferous vegetables, whether they be tried-and-true favourites or new and exciting options. Your body will thank you! And when choosing them, keep these things in mind:

  • adults should have 2 to 3 cups of cruciferous veggies a day; children should aim for 1 to 2 cups
  • look for firm, dark green leaves or heads; try to avoid leaves or heads that are yellow
  • keep fresh cruciferous vegetables in the refrigerator in large, airy plastic bags

Brennan Robertson, Hon. B.Sc. (Nutrition)


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