OVERVIEW
· Antioxidant vitamin pills are flawed, and so we must turn our attention to natural foods to get our fill of antioxidant nutrients.
· We explore the wonderful world of naturally occurring plant compounds, aka ‘phytonutrients’, which have health benefits extending far beyond a simple antioxidant effect.
· Public health messages urging us to eat our fruit and veggies are all very well, but that’s merely the beginning. There’s a lot more we need to know in order to stave off chronic disease.
So, we’ve knocked antioxidant vitamin pills off their perch and concluded that mega-doses of isolated nutrients cause more trouble than they’re worth. That’s not to say we don’t think you should be getting antioxidants, just that they should come the way that nature intended, which is via food. This means that it is time to introduce you to the new and exciting world of ‘phytonutrients’.
Phytonutrients are the components of plant foods that are being extensively researched for their ability to promote health and stave off disease. Unlike the high-dose vitamin pills, these are the naturally occurring compounds we’ve been exposed to through our diets for literally thousands of generations. Common sense should tell us that this has to be preferable to taking something synthesized, mass-produced and taken in the form of a pill.
Whether we’re talking about heart disease or stroke, cancer or diabetes, obesity or osteoporosis, there’s a mass of evidence testifying to the health benefits of having a diet rich in fruit and vegetables. We have campaigns galore to get us eating more of the stuff. The slogans of ‘5 A Day’ in the UK or ‘More Matters’ in the USA have become key public health messages. And who can argue with that? After all, plant foods contain a whole lot of nutrients that are good for our health, such as vitamins, fibre, potassium and, of course, antioxidants. The idea, however, that the health benefits of plant foods is all down to their antioxidant content is a massive over-simplification of the facts. Sure, they’re important but, as we’ll find out, the effect of phytonutrients on our health is much more subtle and intricate.
One thing’s for sure: if you want to take your diet to the next level, it’s time to increase your intake of phytonutrients.
Technicolour diets
When it comes to the modern ‘standard diet’, many people are eating in the televisual equivalent of black and white. More precisely, we’re talking about the atrociously monotonous diets of ‘beige’ foods that are all too prevalent. Based on the mass-produced fodder of white bread, white pasta, potato products, pastries, cookies, cakes and any number of battered and breadcrumbed convenience foods you care to mention, they all have one thing in common – they’re beige and bad for you. These are the archetypal ‘empty calorie’ foods, the enemies of health because they are devoid of vitamins, minerals, fibre and, of course, our newfound friends, phytonutrients. What’s desperately needed in such diets is the injection of some colour courtesy of fruit and vegetables. There’s considerable interest in how the naturally occurring plant pigments in fruit and vegetables could be protectors of our health, so let’s check out a few examples.
One such headline-hitter is lycopene, which is part of the carotenoid family and responsible for the deep-red complexion of tomatoes. The effects of lycopene/tomatoes were demonstrated in a meta-analysis that examined 21 observational studies1. It found that a high tomato intake lowered the risk of prostate cancer by 11%. What’s most noteworthy is that the risk fell further, to 19%, in those who consumed high amounts of cooked tomato products. Because lycopene is tightly bound up in the cells of tomatoes, mechanical processing and cooking frees it up and increases the amount we can absorb. One study observed that men having two or more servings of tomato sauce a week had 23% lower prostate cancer incidence, compared with having less than one serving per month2.
Lycopene is better absorbed from cooked or processed tomatoes. The presence of fat helps to increase the absorption of lycopene, too, so enjoy your tomato dishes with a drizzle of olive oil.
Tomatoes come in three colours: red, yellow and green. Only the red variety provides lycopene.
Along with tomatoes, watermelon and pink grapefruit also offer a handy source of lycopene.
While no large-scale RCTs exist, it is encouraging to note that a study of 32 patients with prostate cancer found that consuming tomato saucebased pasta dishes (providing a bumper 30mg of lycopene per day) decreased levels of PSA, a marker of disease activity3. Prostate cancer isn’t the end of the story either – lycopene has attracted the interest of researchers for a diverse range of benefits, including reducing the risk of cardiovascular disease4, osteoporosis5, and even protecting the skin from the damaging effects of the sun6.
Lycopene is the secret weapon of the junk-food fiend. With its large amount of mechanically processed tomato paste, covered with high-fat cheese, pizza offers one of the most bioavailable sources of lycopene. Tomato ketchup is also up there as a top-notch source, while plain tomatoes in a salad come bottom in the rankings.
So, getting a good dollop of tomato-based products into your diet seems like a good health insurance policy, with lycopene seemingly the star of the show. But don’t think this is all down to lycopene’s ‘antioxidant’ credentials. While lycopene does have antioxidant properties, you only need to consider the fact that vitamin E is found in the prostate at a concentration 180 times that of lycopene to see that it’s unlikely to be the mode of action for lycopene’s purported anti-cancer activity7. And, especially, don’t think it means that a lycopene supplement will confer these same purported benefits.
Attention has now turned to lycopene metabolites, termed ‘lycopenoids’, which may offer benefit8. It may be that other nutrients found in tomatoes are required for this metabolism to occur. Or perhaps we have it totally wrong and lycopene is simply a marker of another unknown nutrient, or combination of nutrients, which does the work. Whatever the reason, it teaches us the age-old lesson that we’d do well to avoid the isolated supplements and stick to the whole food package instead.
Hailing from the same family of carotenoids as lycopene are the yellow pigments lutein and zeaxanthin. Although sunny yellow, they’re tucked away mainly in green leafy vegetables, but are also found in egg yolks. Being the only carotenoids that accumulate in the retina, they are thought to safeguard the eyes from damage by absorbing potentially harmful blue light and quenching excess free radicals. It is postulated, therefore, that these helpful plant pigments may be particularly effective in protecting against age-related macular degeneration (AMD) and cataracts. In a US study of adults aged between 55–80, those with the highest intakes of lutein and zeaxanthin had an impressive 57% lower risk of AMD9. A meta-analysis of such studies concluded that, while benefit was not seen in preventing early AMD, lutein and zeaxanthin intake was associated with significant protection against the development of the more serious late stages10. In a US study of male and female health professionals, those with a high intake of lutein and zeaxanthin had a circa 20% reduction in the rate of cataract formation11,12. And even lutein and zeaxanthin supplements look like they have value, with RCTs now beginning to endorse benefit from supplementation13,14. But with the likes of kale boasting a mighty 18mg/100g lutein and zeaxanthin content, and spinach 11mg/100g15, going for the green leafy vegetables will meet your needs, as well as providing an array of other healthful nutrients besides.
Age-related macular degeneration (AMD) is the leading cause of vision loss among adults. More than ten million people in the USA, and up to 50 million worldwide, suffer with the condition10.
Why stop there? Whether it is anthocyanins giving berries their red, blue or purple hues, or the betalains responsible for the deep red of beets, there’s a veritable smorgasbord of colours to tuck into, which all boast their own unique health benefits.
The ‘f’ word
All in all, adding colour to your diet can go a long way to jazzing up its health credentials. But fruit and veggies are merely the beginning of our quest for a bumper crop of beneficial phytonutrients. This brings us nicely on to the ‘f’ word. Flavonoids represent a rather nifty group of plant compounds found in both fruit and veggies (especially onions, apples, berries and citrus fruits), but also abundant in foods and beverages we may not immediately consider conventionally ‘healthy’, such as green and black tea, red wine and cocoa. These clever compounds are speculated to possess a whole range of benefits to our health – acting as antioxidants, lowering blood pressure, inhibiting inflammation, inhibiting cancer cell growth, and even protecting the brain against neurodegeneration.
We must journey all the way to the San Blas Islands off the coast of Panama to get a better understanding of the health benefits of flavonoids. This is the indigenous home of the Kuna Indians, where high blood pressure is virtually non-existent and, in stark contrast to what we see in the developed world, very healthy blood pressure is maintained even into old age16.
At the turn of the twenty-first century, US Professor Hollenberg and his co-workers unearthed the Kuna’s secret and found that their major source of fluid was a beverage made from locally grown cocoa. The cocoa is fantastically rich in a specific type of flavonoid called flavanols, and the Kuna inhabiting the islands drink in the region of five cups or more of this flavanol-packed beverage daily, providing a staggering 900mg/day. When they migrate to Panama City, however, and consume the processed cocoa available from the local grocery stores (which is devoid of flavanols) instead, their immunity against high blood pressure is lost. Not only that, when Professor Hollenberg and his colleagues looked at the rates of heart disease, diabetes and cancer in the island-dwelling Kuna, they found them to have a remarkably lower risk of death from these diseases than mainland Panamanians. Could it be possible that a diet extraordinarily rich in flavonoids could be potent in protecting against the major diseases of the modern world?
On a weight basis, dark chocolate is only exceeded by a few foods – such as buckwheat hulls, the cereal sorghum and cinnamon – for flavanol content17.
Results from short-term intervention studies lend credence to the findings, showing that cocoa-containing foods and beverages rich in flavanols improve endothelial function, reduce blood pressure and improve insulin sensitivity – all good things when it comes to reducing cardiovascular disease risk18,19,20,21. There is also intriguing data from observational studies, such as a study of elderly men which found that those with the highest cocoa intake had lower blood pressure and almost half as many deaths over a 15-year period22. In another study, consuming chocolate twice or more per week was associated with a 66% reduced risk of cardiac mortality in those who had experienced a first heart attack23.
When it comes to chocolate, flavanols are the ‘Golden Tickets’. But in the words of Charlie Bucket, ‘I’ll bet those Golden Tickets make the chocolate taste terrible’. Well, ‘terrible’ may be harsh, but flavanols do have a bitter, acrid taste, and so manufacturers of chocolate are not keen on keeping too many of them present. Typically, the greater the cocoa percentage the higher the flavanol content, and usually it’s the 50–80% cocoa content that has been shown in studies to confer benefits. But even that’s all very wishy-washy. Just take a look at the results from the USDA analysis of ten cocoa powders. They found a massive range of 0.77–53mg/g (it’s believed the content is 30mg/g in cocoas made by the Kuna Indians)17.
Differences in cocoa beans alone can explain up to fourfold differences in flavanol content24. Furthermore, while processing steps such as roasting, fermenting and dutching may improve flavour, they contribute to a significant loss of flavanols from the final high cocoasolids product. So as a guideline, when it comes to flavanol content cocoa powder is greater than dark chocolate, which is greater than milk chocolate, which is, in turn, greater than white chocolate. But ultimately, ingredient lists are pretty useless for predicting actual flavanol levels. In the words of Professor Hollenberg, ‘What the world needs is a label on each package that describes the flavanol content of the chocolate’25.
When buying cocoa products in the USA, avoid those labelled ‘cocoa processed with alkali’. This process of alkalizing (dutching) massively diminishes the flavanoid content of the product17.
Time for a brew
Cocoa flavanols are just one example of a bountiful group of compounds falling under the umbrella of flavonoids. Tea represents an equally tantalizing flavonoid-rich offering and we’re sure we’re not alone in enjoying a good cuppa. While many people are firmly wedded to a steaming cup of black tea, it seems we would do well to ‘go green’ and sample the toast of the Orient. The flavonoids primarily thought to give tea its health-boosting credentials are a group of compounds called the catechins. And while black tea contains about 3–10% catechins, green tea boasts a whopping 30–40% catechin content.26
Tea is the most commonly consumed drink in the world after water. On average we sip our way through a whopping 40 litres of tea per person every year.
Lemon juice or honey is a good addition to your green tea. The vitamin C from the lemon and sucrose from the honey have been suggested to enhance the absorption of flavonoids and protect them from degradation in the stomach27.
Folklore from Asia tells that green tea consumption began more than 4,700 years ago when the Chinese Emperor Shen Nung (‘Divine Healer’) produced a pleasant, refreshing beverage with green tea leaves by serendipity28. It was much later that the beverage developed its reputation for medicinal and healing prowess. While in the West we have a penchant for the black stuff, in Asia green tea has remained the brew of choice. This habitually high intake of green tea has been proffered to be one of the reasons for the ‘Asian Paradox’: despite an extremely high prevalence of cigarette smoking, Asia, and especially Japan, boasts some of the lowest rates of cardiovascular disease and lung cancer in the world28.
In a Japanese study of 40,530 adults, those that enjoyed five cups or more of green tea daily had a 16% lower mortality rate than those consuming less than one cup per day, and an even more impressive 26% lower mortality rate when looking at just cardiovascular disease29. It was suggested that even one cup of green tea per day may bring benefit. When it comes to matters of the heart, the catechins are thought to exert cardio-protective effects through mechanisms such as inhibiting oxidation, reducing vascular inflammation and preventing blood clot formation30. Green tea also appears to have some cholesterol-lowering effects with a mechanism similar to a weaker version of statin drugs30. When the trials were put together it was found that high green tea consumption reduced the risk of coronary heart disease by 28%, with just a single cup a day associated with a 10% reduced risk31. Alas, no similarly beneficial effect was found in drinkers of black tea.
Decaffeinated green tea contains far lower catechin content, with levels of EGCG (epigallocatechin-3-gallate) approximately one-quarter of caffeinated versions. And bottled green tea is a no-no when it comes to improving health, as its catechin content is virtually non-existent compared to freshly brewed green tea32.
While the Japanese study didn’t find any effect of green tea on cancer mortality, there’s no shortage of evidence from lab and animal studies to say otherwise, with lots of clever mechanisms explaining how components of green tea, most notably epigallocatechin-3-gallate (or EGCG), could fend off cancer33. While this means little on its own, it underpins promising results from the bulk of epidemiological studies. Recently conducted meta-analyses have suggested that green tea consumption may lower the risk of prostate cancer34, stomach cancer35, lung cancer36 and breast cancer37. For breast cancer the greatest benefit may be to prevent recurrence of the disease, with three cups or more a day associated with a 27% reduction in recurrence rate37. Another study raised a provocative finding, with results suggesting that if you start drinking green tea before age 25 the development and presentation of any breast cancer that may have developed in early life will be delayed until later life (post-menopause)38.
Overall, while there seems to be a trend towards benefit in cancer, it is somewhat inconsistent, likely due to different brands and methods of preparation resulting in considerable variation of the flavonoid content in what is considered a ‘standard’ cup of tea. When it comes to RCTs, they are few and small scale. There is definite promise, however, that warrants larger studies. For example, green tea extract has been shown to prevent the development of high-grade prostate intraepithelial neoplasia into full-out cancer. In 60 men with the condition (which is believed to be a precursor to prostate cancer), out of the 30 given 600mg of green tea catechins a day for a year only one prostate cancer case was diagnosed. In the placebo group nine cases out of 30 were diagnosed (a number that would be expected)39. In another study of 39 patients with high-risk oral pre-malignant lesions, benefit was seen in lesion outcome after 12 weeks with green tea extract40.
While green tea has been associated with reduced oesophageal cancer, drinking it at boiling hot temperatures can actually increase your risk41.
Just in case you haven’t been paying close attention, you might be thinking that those few RCTs are an endorsement that you can cut out the palaver of drinking green tea and take a green tea extract in pill form instead. Listen up. When researchers at the US Department of Agriculture’s Agricultural Research Service recently examined 20 commercially available green tea supplements, they found they contained high levels of degradation products, with some even containing unlabelled ingredients. The researchers stated that the level of quality control was unacceptable, and while some decent green tea supplements exist you can’t tell simply by looking at the label42. So, rather than take a supplement, the key is to ensure that you’re brewing up a high flavonoid-content tea. That means not just briefly dipping the teabag. Use hot water (above 70°C) and brew for a few minutes, or long enough to release the catechins, but not so long that the tea becomes bitter and unpalatable.
Flavonoids can bind non-heme iron and inhibit its absorption. One cup of tea with a meal can inhibit iron absorption by up to 90%43. This is especially of concern for vegetarians, making it advisable to avoid consuming tea at meal times, or at the same time as taking iron supplements. Adding a source of vitamin C to your tea or meal (such as lemon juice) can reduce this inhibitory effect44,45.
Flavonoids are a large family with many members and we need to be aware that it’s not just our total flavonoid intake that is important, but consuming a wide variety of different types. Many in the food industry try to put the benefits of flavonoid-rich foods purely down to their antioxidant activity, and imply that you can compare the merits of different foods in this way. As we know by now, all the evidence suggests that this is hogwash, so we urge you to just ignore this type of ignorance.
What doesn’t kill you makes you stronger
We get even further away from the simplified idea that it’s all down to the antioxidants when we look at research on cruciferous vegetables. This is the family of vegetables that includes such notables as broccoli, cabbage, cauliflower, Brussels sprouts, rocket (arugula), watercress and radishes, among others. What makes these veggies special is their rich concentration of a unique group of phytonutrients called glucosinolates, more than 120 different types of which have been identified46. Unsurprisingly, they’re pretty hot property when it comes to research into cancer prevention.
It’s worth taking a look at how this all works. Initially, the glucosinolates are biologically inactive. It’s only when the plant cells get damaged (for example by chewing them), that a specific enzyme, myrosinase, is released. This enzyme transforms the inactive glucosinolates into an active form called isothiocyanates, and these are credited with cancer-protective properties. Indeed, there’s a whole bunch of epidemiological studies that associate consumption of cruciferous vegetables with benefits for a wide range of cancers, such as colon, prostate, breast, bladder, lung, kidney and ovarian47,48,49,50,51,52,53,54,55. There is much less in the way of human intervention studies, although the effects of a 12-month broccoli-rich diet on global gene expression patterns in the human prostate gland found favourable changes to signalling pathways associated with cancer and inflammation56.
Cooking inactivates the myrosinase enzyme, which reduces the amount of isothiocyanates you get from your cruciferous veggies – eating them raw or lightly steamed is best.
It’s when we look at how all this works that things start to get really interesting. Out of the window go simplistic notions that vegetables are good for us because of their antioxidants. It’s a lot more complex than that, with studies indicating that isothiocyanates can prevent the activation of carcinogens in the body and assist it in disarming them46,57. And here’s what we think is a fascinating idea. Maybe isothiocyanates are actually like weak toxins that stimulate the cells of the body to defend themselves and in so doing up-regulate their production of a range of protective enzymes58. Could it be that by inflicting stress on our cells, isothiocyanates elicit a cellular response that makes us more resistant to disease in the long run?
Likewise, when it comes to green tea, don’t be fooled into thinking the purported cancer protective effects come simply from its antioxidant properties. That’s certainly plausible, but it’s likely to be a whole lot more complex than that. Green tea could also work in a more indirect way to stimulate the body’s defence enzymes against cancer, or, intriguingly, it could be its pro-oxidant effects that may help inhibit cancer59. Now you can begin to see how the ‘rich in antioxidant’ marketing slogans are rather absurd.
THE PARTING SHOT
Irish lore states that if you find a leprechaun’s pot of gold hidden at the end of the rainbow, the leprechaun will be indebted to grant your wish. There may be no leprechauns, or pots of gold for that matter, but if you make sure you get the rainbow when it comes to your intake of fruit and veggies, you’ll be well on your way to being granted the wish for good health. We might not know exactly why phytonutrient-rich plant foods are good for us, but we can be pretty confident that they are. What’s also certain is that the vast range of naturally occurring plant compounds we encounter in our diet interact with our biochemistry in intricate and complex ways. The notion that their health benefits can all be pinned down to them being high in antioxidants is a fallacy. Or for that matter, the crass idea that the benefits of such a plethora of nutrients – many of which remain a mystery to us – could be delivered via a pill that merely isolates one or two components.
What this means is that we shouldn’t focus on one single ‘superfood’, or worse still, a single component of a food, as some sort of ‘Holy Grail’ for disease protection because it just doesn’t work that way. The smart money is on spreading your bets and including a broad range of phytonutrient-dense foods in your diet. Above all, remember one thing: it’s whole diets that really count and not isolated components.
SUMMARY AND RECOMMENDATIONS
· Ditch the ‘beige’ and put fruit and vegetables centre stage for a diet packed with colourful phytonutrients.
· Consume two to three tomato-based products/sauces per week for the prostate protector lycopene.
· Protect against age-related macular degeneration by eating dark green leafy vegetables such as kale and spinach.
· ‘Chocolate heals a broken heart’ and a few squares of dark chocolate with a high percentage of cocoa solids (70% or more), or cocoa powder, provide a delicious cardio-tonic.
· Take a leaf from the Orient and swap some of your cups of black tea for green to boost your cardiovascular and cancer defences.
· Make sure your flavonoid intake is diverse; especially rich sources include onions, apples, citrus fruits, berries, legumes, grains and red wine.
· It seems that cruciferous vegetables pack quite a punch when it comes to cancer protection, so aiming for three to five servings a week is a good bet for reducing cancer odds.
· Remember, it is the complex composition of plants that confers protection, so don’t be fooled into thinking that a supplement will ever match, or that ‘antioxidant activity’ claims explain their benefits.