Health Benefits of Green Leafy Vegetables

Greens – A Neglected Gold Mine

Mother was right all along. Grandma also told you they were good for you. So why do Americans eat green leafy vegetables only about once or twice a week? Why are cabbage, broccoli, turnip greens, and spinach rarely seen at the American dinner table? Why is lettuce the only green vegetable that most Americans ever use, when green vegetables are recognized by nutritionists as one of the most inexpensive sources of so many important nutrients?

Green leafy vegetables are a treasure trove of nutrients.

Leafy vegetables are ideal for weight management as they are typically low in calories. They are useful inreducing the risk of cancer and heart disease since they are low in fat, high in dietary fiber, and rich in folic acid, vitamin C, potassium and magnesium, as well as containing a host of phytochemicals, such as lutein, beta-cryptoxanthin, zeaxanthin, and beta-carotene. One study showed that an increment of one daily serving of green leafy vegetables, lowered the risk of cardiovascular disease by 11 percent. In the Adventist health study, the frequent consumption of green salads by African-Americans was associated with a substantially lower risk of mortality.

Because of their high magnesium content and low glycemic index, green leafy vegetables are alsovaluable for persons with type 2 diabetes. An increase of 1 serving/day of green leafy vegetables was associated with a 9 percent lower risk of diabetes. The high level of vitamin K in greens makes them important for the production of osteocalcin, a protein essential for bone health. The risk of hip fracture in middle-aged women was decreased 45% for one or more servings/day of green, leafy vegetables compared to fewer servings.

Green vegetables are also a major source of iron and calciumfor any diet. Swiss chard and spinach are not considered good sources of calcium, due to their high content of oxalic acid. Green leafy vegetables are rich in beta-carotene, which can also be converted into vitamin A, and also improve immune function. Millions of children around the world have an increased risk of blindness, and other illnesses because of inadequate dietary vitamin A from green leafy vegetables.

Lutein and zeaxanthin, carotenoids found in dark-green leafy vegetables, are concentrated in the eye lens and macular region of the retina, and play a protective role in the eye. They protect against both cataract and age-related macular degeneration, the major cause of blindness in the elderly. Some studies suggest that lutein and zeaxanthin may help reduce the risk of certain types of cancer, such as breast and lung cancer, and may contribute to the prevention of heart disease and stroke.

Green veggies contain a variety of carotenoids, flavonoids and other powerful antioxidants that have cancer-protective properties. In a Swedish study, it was reported that eating 3 or more servings a week of green leafy vegetables significantly reduced the risk of stomach cancer, the fourth most frequent cancer in the world. Cabbage, cauliflower, brussels sprouts, and broccoli are rich in indoles and isothiocyanates, which protect us against colon and other cancers. Broccoli sprouts have been reported to contain 10 or more times as much sulforaphane, a cancer-protective substance, than does mature broccoli. A higher consumption of green leafy vegetables has been shown to significantly decrease the risk of breast cancer and skin cancer.

Studies have identified a gene, connexin 43, whose expression is upregulated by chemopreventive carotenoids and which allows direct intercellular gap junctional communication. In many human tumors gap junctional communication is deficient and its up-regulation is associated with decreased proliferation. Hence, the cancer-preventive properties of carotenoids are partly explained by their impact on gene regulation.

Quercetin is a bioflavonoid found in leafy green vegetables. Quercetin has an antioxidant and anti-inflammatory activity and displays unique anticancer properties. Quercetin is a natural compound that blocks substances involved in allergies and acts as an inhibitor of mast cell secretion, and causes a decrease in the release of interleukin-6.

There was considerable concern associated with the E.coli O157:H7 outbreak in the fall of 2006 (26 states were affected) that was associated with contaminated bagged baby spinach. The outbreak resulted in 205 confirmed illnesses and three deaths, with the infection causing bloody diarrhea and dehydration. FDA investigators suggested that the outbreak was possibly caused by the presence of wild pigs on the ranch, or that the irrigation water had been contaminated with cattle feces or grazing deer.

Green, leafy vegetables provide a great variety of colors from the bluish-green of kale to the bright kelly green of spinach. Leafy greens run the whole gamut of flavors, from sweet to bitter, from peppery to earthy. Young plants generally have small, tender leaves and a mild flavor. Many mature plants have tougher leaves and stronger flavors. Collards, Swiss chard, bok choy, and spinach provide a mild flavor while arugula, mizuna and mustard greens provide a peppery flavor. Bok choy is best known for use in stir-fries, since it remains crisp, even when cooked to a tender stage. One should always choose crisp leaves with a fresh vibrant green color. Yellowing is a sign of age and indicates that the greens may have an off flavor. Salad greens provide a whole range of important nutrients and phytochemicals to keep us healthy.

What About These Nutraceuticals?

During the past decade, consumers have begun to view food in a new way. Different foods have been identified as containing health-promoting properties beyond the basic nutritional value of the food. These foods became known to nutrition scientists as functional foods.

Functional foods include tomatoes which contain lycopene, broccoli and cauliflower that contain isothiocyanates, oats which contains beta-glucans, carrots and sweet potatoes which contain carotenoids, spinach and other green vegetables contain lutein, while soy contains isoflavones.

People are encouraged to eat these functional foods to ensure better health. Since many consumers find it difficult to regularly eat some of these functional foods, certain companies have isolated and concentrated the active phytochemicals from the foods to form supplements or nutraceuticals. These dietary supplements supply the phytochemicals in dosages that exceed those obtained from normal foods, and are promoted for the enhancement of one’s health.

But are these nutraceuticals safe and effective? Should we secure the health-promoting phytochemicals from the consumption of whole foods or from the nutraceuticals? There is so much to learn yet about the phytochemicals in our food.

What is the effective dose we need to achieve the health-promoting effects? Are supplements as effective as food, more effective, or less effective than food? Are there synergistic effects between similar phytochemicals in our food? Is the food matrix necessary for effective absorption? Are the phytochemicals altered by food processing? What dose causes toxicity?

There are scores of carotenoids and hundreds of flavonoids present in our food. Which members of these two families of pigments are best absorbed and which ones are the most biologically active? The answers may determine which ones would be packaged as nutraceuticals.

The dietary intake of beta-carotene-rich foods correlates with a reduced risk of various cancers. And so, why not just give people beta-carotene supplements rather than trying to get them to eat foods rich in beta-carotene? Well, several large cancer prevention trials involving beta-carotene have yielded disappointing results. When 20 to 50 mg of beta-carotene was given to subjects for periods of time ranging from 4 to 12 years, the risk of developing lung, prostate, colorectal, and other cancers significantly increased. Sounds like eating the beta-carotene rich foods would be the safest!

The consumption of a therapeutic margarine (such as Benecol, Take Control, or Smart Balance) that contains added plant sterol esters is an effective way to reduce elevated LDL cholesterol levels. However, this practice also depresses blood levels of carotenoids, which somewhat negates the value of the health-promoting effect of the plant sterols.

Tocotrienols are found in rice bran oil, olives, barley and oats. These phytochemicals reduce blood clots, lower LDL cholesterol levels and suppress the onset and proliferation of tumors. However, for full activity the tocotrienols must be fed at low concentrations. At high doses (as in supplements) they convert to alpha-tocopherol (the most common form of vitamin E) which diminishes the beneficial activity of the tocotrienols.

Numerous studies have confirmed that a regular intake of soy protein rich in isoflavones produces a significant decrease in blood cholesterol and triglyceride levels. However, no changes are observed in blood lipids when the isolated soy isoflavones are consumed. Analyses have also revealed that isoflavone supplements on the market are complex mixtures that are poorly standardized.

In summary, the health effects of whole foods tend to be more pronounced than those of the individual components they contain. The effectiveness and safety of nutraceuticals is uncertain at this time. Clinical trials examining the physiological effects of various nutraceuticals have met with mixed and sometimes disappointing results.

Vitamina B12 Para Vegetarianos