There’s a lot more to eating greens than making sure you have enough dietary fibre and vitamin A. I think the majority of people think of their daily vegetables as fairly inert. You find them still and lifeless on the shelves of a supermarket, or cryogenically preserved in the freezer section. And pretty much the same selection with little seasonal variation except the obligatory “offer” on strawberries and raspberries when summer finally arrives.
We know green things are good for us. Spinach is high in vitamin A. But did you know that it is nothing like as high as dandelion leaf? Obviously the phytochemical (plant components) in vegetables vary – the climate, the soil, the season, plant health, length of storage, are all factors that will influence that – but on average fresh spinach contains around 7000-8000 I.U./100g of vitamin A while fresh dandelion leaf contains 10000-14000 I.U./100g. Time and time again, wild greens outperform supermarket greens hands-down. Why is there such a prevalence if iceberg lettuce – nutritional value nearly nil – when there is such a wide choice of excellent alternatives? In mediaeval Britain we ate more ground elder than spinach. Nowadays it is only known as a weed, a pervasive gardeners’ nightmare. But just nibble a leaf. A hint of celery! Cook it exactly like spinach and eat free for six months of the year. I have yet to come across a supermarket that sells ground elder.
However, one wild vegetable has made it onto our tables via the supermarkets and that is rocket or arugula in Italian, even still carrying the title Wild Rocket although it is unlikely that any one went foraging for it! So what’s in rocket?
Vitamin and Mineral Profile (all values per 100g)
Modest, compared to spinach, rocket contains vitamin A 2373 I.U. (mainly lutein & zeaxanthin – 3555 mcg and beta carotene 1424 mcg), so very good for your eye health. Also vitamin K 109 mcg and folate 97 mcg which both help to keep red blood cells growing healthily. Potassium 369 mg, calcium 160 mg, phosphorus, magnesium, sodium, Omega-3 fatty acids 170 mg and Omega-6 at 130 mg There are few carbohydrates 3.7 g (fibre 1.6 g and sugar 2.1 g), protein 2.6 g, no cholesterol and just 25 calories.
You’ll have heard that plants contain groups of phytochemicals like antioxidants, which are good for us. The brassica family (brussells sprouts, cauliflower and broccoli) contain another large group called glucosides where you find sulfur-containing glucosinolates. Rocket also contains these glucosinolates (with less of the sulfurous side effects!). When a plant is chewed by predators such as ourselves, a plant enzyme called myrosinase triggers a change in the glucosinolates, releasing a protective dietary isothiocyanate called erucin. Isothiocyanates like erucin have been found to inhibit the proliferation of cancer cells, such as lung cancer (Melchini et al., 2009).
This is one case though where swallowing a supplement instead, just doesn’t do the trick (Clarke et al., 2011). Supplements don’t contain myrosinase, nor are they chewed, so there is no enzyme nor action available to convert the glucosinolates in these vegetables, into bioactive isothiocyanates like erucin. Unsurprisingly, for the full benefit you have to eat as much of it just as Stone Age man did – raw and without cooking it. Cooking destroys both myrosinase and glucosinolates, which means that you don’t then get the erucin with its protective anti-cancer benefit (Rungapamestry et al., 2007). If you really must cook your veg then steam them, as steaming lead to the lowest loss of total glucosinolates out of all methods of cooking (Yuan et al., 2009). Chewing also makes a difference, as the longer the rocket or broccoli is chewed the more the plant enzyme myrosinase acts on the glucose, and the higher the conversion to erucin (Shapiro et al., 2001). It has also been found that the younger the plant, the higher the concentration of protective plant chemicals it contains, in order to protect the young plant.
So the moral of the story is… Eat lots of young, fresh, raw wild leaves, wild rocket and broccoli and chew well!
Clarke JD, Riedl K, Bella D, Schwartz SJ, Stevens JF and Ho E. (2011) Comparison of isothiocyanate metabolite levels and histone deacetylase activity in human subjects consuming broccoli sprouts or broccoli supplement. J Agric Food Chem. 59(20):10955-63
Melchini A, Costa C, Traka M, Miceli N, Mithen R, De Pasquale R and Trovato A. (2009) Erucin, a new promising cancer chemopreventive agent from rocket salads, shows anti-proliferative activity on human lung carcinoma A549 cells. Food Chem Toxicol. 47(7):1430-6.
Rungapamestry V, Duncan AJ, Fuller Z and Ratcliffe B. (2007) Effect of cooking brassica vegetables on the subsequent hydrolysis and metabolic fate of glucosinolates. Proc Nutr Soc. 66(1):69-81.
Shapiro TA, Fahey JW, Wade KL, Stephenson KK and Talalay P. (2001) Chemoprotective glucosinolates and isothiocyanates of broccoli sprouts: metabolism and excretion in humans.
Cancer Epidemiol Biomarkers Prev. 10(5):501-8.
Yuan G, Sun B, Yuan J and Wang Q. (2009) Effects of different cooking methods on health-promoting compounds of broccoli. J Zhejiang Univ Sci B. 10(8): 580–588.
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