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The colour of healthy eating

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Dear Medical Detective,

Q:I grew up on a dairy farm where my grandfather cultivated the vegetables and fruits we all ate. He never used any fertilizers or pesticides. I remember that I really enjoyed eating the vegetables he grew on his large patch and the fruits from his orchard, but now as an adult, I abhor eating fruits and vegetables! Do you have any thoughts about why my taste buds changed so much as an adult? And I know I should get my ‘five a day’, but which five?

-R.N., Winchester, Hampshire

A:These days almost everything is heavily sprayed with pesticides, and manure has been replaced by artificial fertilization, a method that leaches the soil of minerals and nutrients.

During my 40-year experience as a clinician I have noticed that all too often the pesticide residues left on fruits and vegetables seem to gradually produce an aversion to them. The good news is that this can slowly be reversed over a year by switching back to organic produce, which will eventually reestablish your original taste for fruits and vegetables.

One way to stimulate your taste buds is to create a really colourful potpourri on your plate every day. In fact, there are many good health reasons for choosing the brightest coloured fruit and vegetables.

Polyphenols, glucosinolates, phytoestrogens, saponins and many other ‘secondary’ components of fruit and veg used to be regarded as useless by many food scientists because they didn’t deliver energy and weren’t indispensible to life like vitamins are. Today we know that these secondary plant components contribute significantly to our health status: they affect our immune system, lower our cholesterol and blood pressure, and may even act as an effective cancer preventative.

They are ‘secondary’ because, unlike the plants’ principal constituents (carbohydrates, fat and proteins), these ‘secondary metabolites’ appear only in minute amounts and only in certain plants, and they aren’t essential for the plant’s own survival. Nevertheless, a number of the secondary colour-giving plant components are antioxidants, stopping those so-called ‘free radicals’ from combining with other molecules and causing cellular and tissue damage. Other aromatic substances, which give certain plants like onions and garlic their pungent smell, also offer powerful health-giving effects.

Here are just a few examples of why the most colourful and aromatic produce are best for you.

Start with yellow, orange and red-the colours of carotenoids. Carrots, apricots, kiwis, pumpkins, tomatoes, mangoes, melons, red bell peppers, broccoli, Chinese kale, spinach, red cabbage and savoy cabbage all contain copious amounts of the natural carotenoids lycopene, zeaxanthin, lutein and carotene, all known to inhibit inflammation. They also lower the risk of cardiovascular disease and, in the over-70s, reduce the risk of cancer; there’s even some evidence that natural carotenoids may reduce the risk of eye diseases like cataract and macular degeneration.1

Add a touch of blue, bright yellow, red and violet-the colours of polyphenols. Apples, aubergines (eggplants), quinces, berries, pomegranates, green cabbage, cherries, plums, radishes, rhubarb, red cabbage, chives, grapes, tomatoes, onions, coffee, pears, red wine and grape juice are all full of polyphenols. Their beneficial effects are antibiotic, strongly antioxidative and anti-inflammatory; one polyphenol called quercetin acts as an antihistamine. Polyphenols are known to act preventatively against thrombosis (clots), and to lower blood pressure, improve blood circulation, and significantly reduce the risk of breast and colon cancers.2

Turbocharge yourself with terpenoids.The odour associated with pineapples, apricots, caraway seeds, tangerines, peppermint, radishes, oranges, celery, grapes and limes is derived from their natural terpenoid lemonal, citral or menthol contents. These furnish antibiotic, anti-inflammatory and LDL-cholesterol-lowering effects while stimulating body metabolism, and there’s some evidence they may reduce your cancer risk.3 But bear in mind that terpenoids dissipate into the air rather quickly, so these foods need to be eaten immediately after they’re prepared.

Scent food with super sulphides.Red onions, scallions, green chives, leeks, garlic and shallots all contain allicin, which is highly antioxidative and antibiotic. More than a thousand studies have shown that these vegetables reduce the risk of cardiovascular disease, slow blood coagulation (blood-thinning), help protect blood vessels and lower the risk of certain cancers.4 To release these good effects, you need to cut or grate these foods and eat them fairly soon after.

Boost yourself with the ‘bitters’.Pulses, peanuts, oats, (non-GMO) soya and asparagus are full of saponins, which have mildly anti-inflammatory effects and might cut the risk of colon cancer.5

Go green-the colour of protection.The mainly green cruciferous vegetables (like cauliflower, broccoli and Brussels sprouts; see page 55) contain the powerful mustard oil glycosides, or glucosinolates, which are strongly antimicrobial and antioxidative, as well as protective against infections. They may also lower the risk of breast and lung cancer. Broccoli, Brussels sprouts and cabbage have some evidence of reducing the risk of cancer at a variety of organ sites, and regularly eating broccoli can also lessen flare-ups of diarrhoea and abdominal pain in Crohn’s disease.6

Chomp your hormones back into balance.Many plant foods that are slightly crunchy like pulses and pumpkin, sunflower and sesame seeds contain phytosterols, chemicals that resemble human cholesterol; legumes (like peas and beans) as well as cruciferous vegetables, flaxseed, red clover and (non-GMO) soybeans also contain phytoestrogens, which affect the immune system and protect against prostate, breast, bowel and other cancers, as well as cardiovascular disease, many brain function disorders and osteoporosis.7

All of these secondary plant components are generally in or just under the peel, so make sure you wash or scrub these organic fruits and vegetables, rather than peeling them, and don’t leave them in water for too long or store them in sunlight. Be sure they have ripened fully and haven’t been picked too early, and opt for local and home-grown over supermarket produce flown in from other continents. Carotenoids, saponins and phytoestrogens can put up with the cooking process, but the rest don’t tolerate any heat. Glucosinolates (the ones found in cruciferous veg) are water-soluble and dissolve into the cooking water, so use this as a base for your sauces and soups.

The entire idea of ‘five a day’ is a cheap PR catchphrase thought up by the government, but you may have noticed that almost every one of the secondary components in fruit and veg protect against cancer. That’s the one-a-day reason I’d choose to make at least five of these foods part of my daily plate.


  1. Nutr Clin Care, 2002; 5: 56-65
  2. Am J Clin Nutr, 2004; 79: 727-47
  3. Harrewijn P et al. Natural Terpenoids as Messengers: A multidisciplinary study of their production, biological functions and practical applications. Dordrecht: Springer Verlag, 2001
  4. http://www.allicinfacts .com/garlic-studies/research-highlights
  6. Eur J Nutr, 2008; 47 Suppl 2: 73-88; Gut, 2010; 59: 1331-9
  7. Yildiz F, ed. Phytoestrogens in Functional Foods. Boca Raton, Florida: CRC Press, 2005

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Article Topics: Brassica oleracea, nutrition
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