To scientists, cabbage is a vegetable that contains large quantities of several anticancer compounds that prevent carcinogenic substances causing cell damage. To the ancient Greeks, however, cabbages were the stuff of legend.
A Greek story based on the tales in The Iliad claims that Dionysus, the god of the grape harvest, was rather badly received on his way through Thrace. The warlike Lycurgus, king of the Edonians, beat back the god’s army using his cattle prod, forcing Dionysus to take refuge in the grotto of Thetis, the sea nymph. Driven mad by this victory, however, Lycurgus began to destroy what he thought were the god’s sacred grape vines, but which were in fact the feet of his own son, Dryas. Dionysus punished the king for this sacrilege by bringing a terrible drought on the Thracian people. Once aroused, his anger could only be appeased by having Lycurgus put to death. Tortured and then dismembered by the Edonians, Lycurgus wept in agony before dying. Where his tears fell, there sprouted cabbages.
Far from being the only fanciful story associated with cabbage, this legend nonetheless reflects the important role played by this vegetable in the history of European and Mediterranean civilizations. Cultivated for more than 6,000 years and, as a result, likely the elder statesman of our vegetables, cabbage is found everywhere, both in the history of food and in ancient and medieval literary traditions. As the French physician, writer and humorist Francois Rabelais (1494—1553) wrote in The Adventures of Pantagruel. “O thrice and four times happy those who plant cabbages,” since its cultivation was a symbol at that time of tranquility and pacifism.
However, these vegetables are not among the foods that arouse the most passion and enthusiasm in many people, to say the least! Tasteless to some, lacking in delicacy to others, cabbage and its cousins are to a greater or lesser degree disliked by some people. Yet, harvested at the right time and prepared properly, they can be a real treat, especially since they are among the foods with the greatest ability to effectively ward off the development of cancer.
Cabbage is the prototype of a family of vegetables called crucifers, a term that describes the cross-shaped flowers the plant produces in order to reproduce. Even though it may at first be hard to believe, the main species of cabbage found today— broccoli, cauliflower, Brussels sprouts, kale, and so on—are all direct descendants of wild cabbage. From this plant (Brassica oleracea) which still grows wild on the rugged terrain of the rocky hills and cliffs of the Atlantic coast of Europe and the Mediterranean, humans domesticated cabbage and forced evolution’s hand by selecting, about 4,000 years ago, specimens with very specific quantities that satisfied the culinary preferences of peoples in the region. For example, the Romans seemed to prefer a cabbage with massive flowers an succeeded in developing the first varieties of broccoli and, later on, cauliflower. The diversification of the Brassica species must have been an extremely important activity in antiquity, for specialists believe that most species of cabbage now known already existed in the Roman era, three centuries BCE.
THE ANCIENT GREEK AND ROMAN VIEW
In ancient times, it seems that plants in the crucifer family were mainly grown for their medicinal properties. Beginning with mustard, cultivated in China more than 6,000 years ago, and followed by the various forms of cabbage described by Greek and Roman botanists, cultivation basically aimed to produce plants to treat various disorders, from deafness to gout, as well as gastrointestinal problems. Cabbage, in particular, was considered to be a very important medicinal food for the Greek and Roman civilizations, even replacing garlic, at one point, as the favorite remedy. It was praised by the scientist Pythagoras (570-377 BCE) and called “the vegetable of a thousand virtues” by Hippocrates of Kos (460-377 BCE), considered the founder of Western medicine. He recommended it as cure for diarrhea and dysentery, among other things. Diogenes the Cynic (413-327 BCE), who lived to the venerable age of 83 and had only a poor barrel as his dwelling, ate almost nothing but cabbage. Clearly, this vegetable was seen at the time as a key food for good health.
Marcus Porcius Cato, or Cato the Elder (234-149 BCE), a very powerful Roman statesman who occupied the honorable yet most feared of all posts – that of censor, the magistrate notably responsible for establishing taxation levels – was the first to use the term Brassica (from the Celtic bresic, meaning “cabbage”), still used today to designate the vegetables in this family. Highly suspicious of doctors, all of whom were Greeks at the time, Cato viewed cabbage as a universal remedy for disease, and a true fountain of youth responsible for his good health and virility (he fathered a son at the age of 80). While he filled his leisure time by growing more than 100 medicinal plants, Cato wrote in De agri cultura (his treatise on agriculture) that “eaten raw with vinegar, cooked in oil or fat, cabbage eliminates everything and cures everything,” from a hangover caused by too much wine to a number of serious illnesses. According to Cato, applying a crushed cabbage leaf soothed ulcers on the breasts. While we now have more effective modern means to treat breast cancer, the role cabbage performed as a cure for indulgence in too much alcohol seems to have come down through the ages, judging by the recent appearance on the Russian market of a salty beverage made from cabbage juice and designed to alleviate those unpleasant post-celebration aftereffects.
THE ANTICANCER EFFECTS OF CRUCIFEROUS VEGETABLES
Studies done to date indicate that cruciferous vegetables are among the main sources of the anticancer properties that can be gained by eating fruits and vegetables. For example, in the course of study analyzing 252 cases of bladder cancer in 47,909 health professionals over a period of 10 years, eating five or more servings of cruciferous vegetables a week, especially broccoli or cabbage, was associated with cutting the risk of bladder cancer in half compared with individuals who only ate one serving or less of these vegetables. The observation was the same for breast cancer: Swedish women who ate the most crucifers, one or two servings a day, saw their risk of developing breast cancer halved compared with those who ate none or few. Without listing all of the studies suggesting that cruciferous vegetables have a real cancer-fighting effect, it must be pointed out that eating them regularly has also been linked with a lower risk of several other cancers, such as those of the lung, the gastrointestinal system (colon, stomach, rectum), and the prostate.
In the latter case, three or more servings of cruciferous vegetables per week have even been shown to be more effective in preventing prostate cancer than eating tomatoes, often suggested as a food that stops this disease from developing.
A protective effect of crucifers is also observed in the prevention of recurrences (known as secondary prevention) in people with some types of cancer. For example, patients with bladder cancer who eat at least one serving of broccoli a week see the risk of mortality linked to this cancer decrease by 60 percent. In the same way, studies indicate that breast cancer survivors who eat three servings of crucifers weekly have a 50 percent lower risk of recurrence. So, while the quantity of fruits and vegetables in the diet definitely plays a key role in preventing cancer, studies indicate that some kinds of vegetables, especially crucifers, are particularly important for halting the development of the disease. These observations are critical in the context of the Western diet, and especially in North America, where potatoes make up as much as 50 percent of daily fruit and vegetable intake and cruciferous vegetables still play only a very limited role.
PHYTOCHEMICALS IN THE CABBAGE FAMILY
As we have shown, regularly eating vegetable in the cabbage family dramatically decreases the risk of developing several cancers. This evidence suggests that this type of vegetable is a significant source of Phytochemical compounds. In fact, of all the plants eaten by humans, cruciferous vegetables probably contain the great variety of phytochemical molecules with anticancer properties. In addition to several polyphenols found in other protective foods, discussed later, cruciferous vegetables also contain a group of compounds called glucosinolates. These molecules are especially plentiful in Brussels sprouts and leafy cabbages (kale and spring greens), but they are also found in significant amounts in all crucifers.
Unlike most of phytochemical compounds we will describe in the following chapters, the importance of gIucosinolates in cancer prevention through food is not directly linked to these molecules. Instead, they work by releasing two classes of compounds, known as isothiocyanates and indoles, that have very powerful anticancer activity.
More than one hundred glucosinolates occur in nature, acting as a “reservoir” for storing many different isothiocyantes and indoles, all with very high anticancer potential. The process of chewing the vegetable crushes the plant cells and mixes up the various compartments in the cells normally separated from one another.
Glucosinolates that were stored in one of the compartments of broccoli cells are thus exposed to myrosinase, an enzyme found in another compartment whose role is to cleave off some parts of the glucosinolate molecules. When broccoli is chewed, the vegetable’s main isothiocyanate glucoraphanin, suddenly finds itself in the presence of myrosinase and is immediately turned into sulforaphane a powerful anticancer molecule. To put it another way, the anticancer molecule in cruciferous vegetable occur in an inactive state in whole vegetables out chewing these vegetables releases active compounds that can then carry out the anticancer functions described later.
Because of the complexity of this mechanism, several factors must be kept in mind in order to get the full benefit of consuming isothiocyanates and indoles. First of all, it is important to remember that glucosinolates are very soluble in water, o cooking crucifers in a large volume of water for just 10 minutes cuts the quantity of glucosinolates in these vegetables by half and should therefore be avoided. Secondly, myrosinase activity is very sensitive to heat, so prolonged cooking of vegetables, whether or not in a large volume of water, substantially reduces the quantity of isothiocyanates that can be released when the vegetable is chewed. Studies suggest that some of the bacteria in the intestinal flora might change glucosinolates into isothiocyanates and thus make up for the inactivation of the vegetable caused by heat, but such a role still requires further study.
To reduce the loss of myrosinase and glucosinolate activity caused by immersing these vegetables in water and boiling them, cook cruciferous vegetables as little as possible, and in a minimum of water. To maximize the number anticancer molecules supplied by cruciferous vegetables, as well as making them more attractive and enjoyable to eat, simply steam them on the stove or in a microwave, or stir-fry them. In addition, avoid eating frozen cruciferous vegetables because these are put through a high-temperature blanching stage during processing, which reduces both their glucosinolate content and their myrosinase activity. The result is that frozen vegetables are definitely inferior to fresh as a source of anticancer molecules. Lastly, to promote the release of active molecules, remember to chew your vegetable well before swallowing them.
SULFORAPHANE, STAR OF THE ISOTHIOCYANATES
Isothiocyanates contain in their structure an atom of sulfur. This is the main cause of the unmistakable odor produced by overcooking cabbages and their cousins. Since each isothiocyanate is derived from a different glucosinolate, the nature of the isothiocyanates associated with cruciferous vegetables obviously depends on the nature of the glucosinolates in these vegetables. Some glucosinolates are found in almost all cruciferous vegetables, while other members of this contain very high levels of a specific type of glucosinolate, and therefore of the corresponding isothiocyanate. These differences in composition are important, since some isothiocyanates have more powerful anticancer properties than others. This is especially the case for the sulforaphane found in broccoli. Sulforaphane was isolated for the first time in 1959 from whitetop, or hoary cress (Cardaria darba), where it occurs in very large quantities. From a nutritional point of view, broccoli is by far the best source of sulforaphane, providing up to 60 milligrams of this molecule per serving. It is also worth knowing that broccoli sprouts can contain up to 100 times more sulforaphane than mature broccoli.
Sulforaphane, and therefore broccoli, deserves special consideration in any dietary strategy for preventing cancer. A number of results obtained through research during the last 20 years indicate that sulforaphane considerably speeds up the body’s elimination of toxic substances with the potential to cause cancer. Studies in animals have emphasized how extremely important this is. Researchers have seen that increasing the effectiveness of detoxification systems by means of sulforaphane clearly reduces the occurrence, number, and size of mammary tumors caused by certain carcinogenic substances in rats and mice. As we have already seen, scientific studies indicate that this anticancer effect applies equally to humans.
Sulforaphane also seems to be able to act directly on cancer cells and cause their death by triggering the apoptosis (cell suicide) process. In a series of studies on the ability of substances of nutritional origin to cause the death of cells isolated from an infantile brain tumor, called a medullablastoma, we have observed that sulforaphane is the only molecule of nutritional origin tested able to cause cell death.
The ability of sulforaphane to cause the death of cancer cells has also been observed for other kinds of tumors, such as cancers of the colon and prostate, as well as in the case of acute lymphoblastic leukemia. This suggests that the direct action of the molecule on tumor cells contributes to its anticancer properties. Sulforaphane also has bactericidal antibiotic properties, especially against Helicobacter pylori, the bacterium that causes gastric ulcers. At first glance, it would seem that this activity is not directly related to cancer. However, such an activity could play a very important role in protecting against stomach cancer. Researchers now believe that being infected with H. pylori, with the resulting gastric ulcers, increases by three to six times the risk of getting stomach cancer. Eating broccoli puts sulforaphane in direct contact with the bacteria in the stomach and can stop the development of this disease at the source.
All of these properties make sulforaphane the isothiocyanate with the most powerful anticancer potential. In turn, this makes broccoli, the source of this molecule, one of the most important foods for preventing the appearance of several cancers.
Despite all of the beneficial properties associated with sulforaphane, it would be incorrect to think that eating broccoli regularly can by itself help prevent cancer. However, the isothiocyanates and indoles occurring in other members of the crucifer family also have many anticancer properties, which apparently contribute to the protective effects of these vegetables. Among these molecules, two deserve special attention: phenethyl isothiocyanate (PEITC) and indole-3-carbinol (I3C). Phenethyl isothiocyanate (PEITC). PEITC is a molecule formed from gluconasturtiin, a glucosinolate found in large quantities in watercress and Chinese cabbage. Just like sulforaphane, PEITC cancers caused by exposure to toxic substances, especially cancers of the esophagus, stomach, colon, and lung. In the latter case, some studies have shown that an increased intake of mustard sprouts in the diet of a group of smokers (60 grams per meal for three days) was linked with a decrease in the toxic forms of NNK, a carcinogenic nitrosamine in tobacco.
Given the very strong carcinogenic potential of NNK, these results clearly illustrate the degree to which isothiocyanates act as powerful protective agents against the development of tumors caused by carcinogenic substances. It seems more and more certain that PEITC’s anticancer mechanism might also involve direct action on cancer cells. Because of the molecule’s ability to force the cells to die through apoptosis, PEITC is in fact one of the isothiocyanates that cancer cells find most toxic, especially leukemia cells and those in colon, breast, and prostate cancers. This property suggests therefore that PEITC might not only prevent tumors from developing, but may also play a preventive role even earlier in the process, killing off precancerous cells before they begin to develop into tumors. Recent observations do indeed indicate that PEITC isable to eliminate cancer stem cells, a subpopulation of tumor cells that often resist anticancer treatments and cause cancer recurrences.
These observations indicate that dietary sources of PEITC, such as watercress, can therefore be an additional barrier against the development of certain types of cancer, both because of their ability to counteract the action of highly carcinogenic substances and due to their toxic effect on cancer cells.
Indole-3-carbinol. Even though it is a product of the hydrolysis of glucosinolates, like isothiocyanates, I3C is different from this class of molecules, both in its chemical structure (without any sulfur atoms0 and its anticancer mode of action. I3C is derived from the degradation of glucobrassicin, a glucosinolate found in the vast majority of cruciferous vegetables (although it is slightly more plentiful in broccoli and Brussels sprouts).
More recent research into the cancer-preventive role of I3C shows an impact on estrogen metabolism and its ability to interfere with estrogen-dependent cancers like those of the breast, endometrium, and cervix. In fact, it seems that I3C has the ability to case changes in the structure of estradiol that reduce this hormone’s ability to encourage cell growth in these tissues. This effect is clearly illustrated by results showing that cells in the cervix containing human papilloma virus (HPV) – 16 (the main cause of this cancer) and able to develop into cancer cells after estrogen treatment see their growth halted by the administration of I3C.
In conclusion, the diligent efforts made by our far-off ancestors to produce all of these varieties of cabbage were certainly worth the trouble, when we consider the exceptional phytochemical content of these cruciferous vegetables, especially glucosinolates and their active forms, isothiocyanates and indoles. Including these vegetables in the diet is therefore an easy way to supply the body with generous amounts of these molecules and, as a result, prevent the development of several cancers, especially in the lungs and gastrointestinal tract. Currently available scientific findings are particularly encouraging. For example, a diet containing three or four servings of broccoli a week, which is far from excessive, has proven to be enough to protect people from developing colon polyps, a significant stage in the onset of cancer in this organ. Finally, the inhibiting action of some components of crucifers of estrogen makes these vegetables essential players in the fight against breast cancer.