Cruciferous Vegetables: Nutritional Powerhouses
With the growing baby boomer population reaching retirement age at increasing numbers, there is a greater interest in “preventative medicine.” The evidence is steadily growing that, not too surprising, a majority of diseases can be attributed to our diet. In fact, the American Cancer Society puts a number on it. It estimates that more than two-thirds of cancer may be prevented through lifestyle modification, and nearly one-third of these cancer occurrences can be attributed to diet alone.
Scientists have recently drawn more of their attention to a group of vegetables called the cruciferous vegetables that have appeared to show some impressive cancer preventative, cancer-inhibiting and anti-inflammatory results.
They get their name because their four-petal flowers resemble crosses. Cruciferous vegetables include arugula, broccoli, cauliflower, brussel sprouts, cabbage, watercress, bok choy, turnip greens, mustard greens, collard greens, rutabaga, napa or Chinese cabbage, daikon, wasabi, radishes, turnips, horse radish, kohlrabi, and kale.
Cruciferous vegetables differ from other classes of vegetables in that they are rich sources of sulfur-containing phytonutrients known as glucosinolates (GLS). The science is getting deep investigating these and their abilities.
In order for the beneficial effects of GLS to be unleashed, the cell walls must be disrupted by chewing or cooking, activating an enzyme called myrosinase. The GLS are quickly broken down into the reactive compounds. Various forms of GLS break down into various forms of such chemicals called isothiocyanates, flavones, phenols and indoles. These products, could help prevent cancer by enhancing the elimination of carcinogens before they can damage DNA, or by altering cell signaling pathways in ways that help prevent normal cells from being transformed into cancerous cells. Some GLS products, such as indoles, may alter the metabolism or activity of hormones like estrogen in ways that inhibit the development of hormone-sensitive cancers, such as breast cancer. Each of these breakdown products of GLS has its own protective ability.
Therefore, we should certainly not eat a single kind of cruciferous vegetable and believe that we are getting the true benefits of all of them. Variety is very important. The National Cancer Institute has linked the cruciferous vegetables to a reduced risk of colon cancer and protective effects against cancer of the lung, esophagus, larynx, rectum, colon, lung, stomach, prostate, and bladder.
However, there is another side to this. Unfortunately, this protective benefit against cancer has been determined to be largely dependent on an individual’s genetic makeup. Individuals that lack the gene that metabolizes GSL products, such as isothiocyanates, will result in a greater concentration of isothiocyanates in their blood, resulting in longer exposure after cruciferous vegetable consumption. There are several studies that show this is why some individuals had greater protection from lung cancer and colon cancer. Therefore, some of us may benefit more from cruciferous vegetable ingestion than others; but no matter what, we all will benefit from them at some level.
GLS Content in Cruciferous Vegetables
Unlike some other phytochemicals, GLS are present in relatively high concentrations in commonly consumed portions of cruciferous vegetables. For example, ½ cup of raw broccoli might provide approximately 27 mg of total GLS. On the other hand, ½ cup of raw brussel sprouts contains 104 mg of total GLS.
The amounts of isothiocyanates formed from GLS in foods are variable and depend partly on the processing, age and preparation of those foods. Consumption of 5 or more weekly servings of cruciferous vegetables has been associated with significant reductions in cancer risk in some prospective cohort studies. Glucosinolates are water-soluble compounds that may be leached into cooking water. Boiling cruciferous vegetables from 9-15 minutes will result in a loss of GSL content, up to 58% loss. Cooking methods that use less water, such as steaming or microwaving may reduce GSL losses. So for the sake of retaining GSL content, eating these vegetables raw is best.
Some cooking practices, including boiling, steaming and microwaving at high power (850-900 watts) may inactivate myrosinase, the enzyme that breaks down GLS. Never fear. Without myrosinase, the bacteria in our gut will still break down some of the GSL into a beneficial product. However, inactivation of myrosinase in cruciferous vegetables substantially decreases the concentration of isothiocyanates. Once again, raw is best. Unfortunately, for many, cruciferous vegetables are not as tasty as other vegetables, so people may have a difficult time wanting to eat them, especially in their ideal, raw state. This can be treated with mild amounts of fat-free dressings, dips, cottage cheese or flaxseed oil. Be creative and try to have these regularly in your refrigerator. Healthy eating should not be synonymous with “difficult eating.”
Can I take a Supplement Instead?
Below is a list of other compounds and chemicals not previously mentioned that are naturally found in cruciferous vegetables with a brief description:
Vitamin A – a fat-soluble antioxidant that helps protect skin and proper cell reproduction.
Vitamin C – a water-soluble antioxidant that has a role in connective tissue repair
Vitamin E – a fat-soluble antioxidant that protects cells from damage
Folate – a B-complex vitamin that is involved in proper DNA metabolism
Selenium – a trace mineral involved in selenium-dependent enzyme functions.
Potassium – an electrolyte
Carotenoids – pigments synthesized by plants that may help form vitamin A and act as antioxidants alone. Research is not sure on all of their roles as being anti-carcinogenic.
Chlorophyll – a photosynthetic pigment that may have anti-cancer effects
Fiber – compounds that regulate blood sugar, slow digestion, decrease cardiovascular disease and aids in fat loss.
Flavonoids – plant compounds that are anti-aging and reduce the risk of chronic disease.
Indole-3-Carbinol – may inhibit cancer development in humans, especially reproductive cancers. This still needs further study in humans.
Lignans – may have a role in the prevention of hormone-associated cancers, osteoporosis, and cardiovascular diseases, but it is still not understood.
Phytosterols – inhibit cholesterol absorption and may help urinary functions with a benign, enlarged prostate. As you can see, these vegetables are quite the powerhouses full of nutrients.
No matter what your fitness goals are or if you just want to live a healthy lifestyle, these should be on your plate every day. Because there are so many nutrients in cruciferous vegetables, scientists do not necessarily believe it is only the broken down GSL-products that benefit us, but it may be an interactive effect among several vitamins, minerals and phytonutrients that create the cancer-protective environment within us. Further research is still needed to better understand this.
Therefore, taking a supplement of just one of these GSL-products may not be recommended, especially an extract that utilized heat to create its supplement. This may have deactivated myrosinase, or the ingredient itself, leaving the responsibility of the conversion of GSL-products to our gut bacteria. In the end, if your diet is poor, something is better than nothing. Ideally, a wide variety of raw or lightly cooked cruciferous vegetables is just what you should eat.
Summary and Recommendations
Unlike other vegetables, cruciferous vegetables contain a class of a sulfur-compound called glucosinolate. After chewing these and breaking the cell walls, these are broken down by myrosinase into a number of anti-cancer, anti-tumor, and anti-inflammatory phytonutrients. Some of these phytochemicals stop carcinogens before they have a chance to alter DNA structure. Others slow the development or spread of cancerous cells or stimulate the release of anticancer enzymes. Indoles increase the detoxification of estrogen, reducing that hormone’s chance of enhancing cancer growth in hormone-sensitive cells. This is believed to be only the tip of the iceberg for the number of benefits associated with cruciferous vegetables.
Although many organizations, including the National Cancer Institute recommend the consumption of 5-9 servings of fruits and vegetables daily, separate recommendations for cruciferous vegetables have not been established. For now, some scientists recommend 5 weekly servings of just cruciferous vegetables alone. Happy eating!