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Foods rich in anti-oxidants and phytochemicals usually have a wide range of anti-cancer properties which are described below. The antioxidant element of there food are thought of wield their anti-cancer properties by directly or indirectly counterbalancing the super oxide free radicals produce from carcinogens in our diet or other environmental factors. The section on what is cancer  explained how these free radicals damage the DNA, rearranging the genes within the cells leading to the development of cancer. 

Although patients with established cancer have already sustained the DNA damage in order to mutate from benign to malignant cells, the cancer process is by no means over. Avoiding further DNA insults avoids further mutation which can encourage indolent (less aggressive) malignant cells or pre-malignant cells into transform into more aggressive types which are more likely to grow and spread faster. Anti-oxidants, otherwise known as free radical scavengers are found in a wide variety of dietary sources. Foods which naturally contain a high percentage of antioxidants have more recently been nick named “superfoods”. A wide variety of foods have anti-oxidant properties including vitamins but convention tends to separate the main categories into three groups;

Phytochemicals otherwise referred to as polyphenols are basically the scientific chemicals which come from plants and are traditionally in the category which do not act via a hormonal route but have been shown to have some direct anti cancer effect via an antioxidative or antiproliferative (slows cell growth rate) effect. They include the phenolic acids namely benzoic acid (hydroxybenzoic acid, gallic acid) and cinnamic acid (caffeic and quinic acid), together with the non-oestrogenic flavanoids including anthocyanidins, the flavanols (catechins and proanthocyanidins), lignans and stilbens. Kaempferol found in broccoli and kale has particularly been shown to reduce the risks of ovary and breast cancer within a large study of dietary patterns among nurses (The Nurses Health Study). Legumes such as bean and pulses, nuts and cereals have been shown to be rich in the phytochemical, inositol pentakisphosphate (InsP5). This chemical has been shown in mouse models to significantly inhibit the growth of cancer cells. It also appears to enhance the beneficial effects of chemotherapy without increasing their side effects and further development of this compound is being investigated for future clinical use. Researchers in Leicester University, UK have postulated following an environmental study of the local population that the antioxidants found in spices such as capsaicin, the chemical responsible for the heat in chillies, and curcumin, the chemical that gives turmeric its yellow colour are thought to be responsible for the low levels of colon cancer in the Asian community. In the USA a team in Columbia University are investigating a combination of turmeric and ginger. Although initially given for arthritis it has been shown in laboratory tests to reduce prostate cancer cell growth by 78% and significantly increase the rate of programmed cell death (apoptois). Drinks such as traditional green and black tea, contains a variety of phytochemicals of which the polyphenol epigallocatechin gallate is the most abundant. Many other fruit and herbal teas are also now commercially available. Healthy phytochemicals can also be found in less obvious sources such as coffee, chocolate, cider some beers, and the tannin component of red wine. The benefits of this later group have to of course be balances with the risks of alcohol, fat, carcinogens and sugar. In general foods with a high polyphenol concentration include:- 

  • Green vegetables; cabbage, spinach, broccoli,
  • Salad; Dark green lettuce leaves (rocket), leaks, onions, celery
  • Citrus fruits (especially ripe); pomegranates, kiwis, plums, apples, lemons, apricots, plums, pears, oranges, nectarines, strawberries, bananas, grapes.
  • Mushrooms; white and wild varieties
  • Dried fruits; raisin, prunes, apricots.
  • Berries: Cherries, blueberries, blackberries, cranberries, goji berries, gac.
  • Legumes; beans, lentils, chick peas
  • Nuts: Hazelnuts, peanuts, cashews.
  • Herbs & spices; Garlic, parsley, mint, coriander, thyme, rosemary

There is much we still do not know about the anti-oxidant and anti-proliferative affects of food but in an attempt to introduce some order to the discussion the Food and Drug Administration (FDA) the American food and drug regulatory authority have published league tables of foods ability to scavenge and remove the DNA damaging free radicals. The tables rank food according to their Oxygen Radical Absorbance Capacity (ORAC).  The best contenders being goji berries, prunes, flaxseed, linseeds, nuts, dark greens, cruciferous, brightly coloured vegetables, berries, fruits and grains. As these have high ORAC ratings they have been nicknamed superfoods.

Carotenoids: Lycopene and beta-carotene, are naturally occurring yellow, orange and red plant pigments found in chillies, tomatoes, peppers, carrots and other colourful foods. As well as protecting people form cancer by promoting the antioxidant enzymes, there is growing evidence from laboratory experiments that they also have been shown to stop cancer cells progressing to a more aggressive form (becoming less differentiated). Other experiments have also shown that carotenoids slow the rate cancer cells divide and multiple (reduce proliferation) and both these actions may be independent of their free radical scavenging benefits. In men with prostate cancer, lycopene, predominant in tomatoes and chillies, concentrated in processing, has been shown to have a protective benefit on prostate cancer risk among U.S. health professionals. For men with established cancer, two small non-randomised studies looked at natural lycopene intake in food, particularly tomato sauce, and demonstrated a slowing of the rate of rise of the cancer marker Prostate Specific Antigen  (PSA).

It is thought that the most effective protection from carotenoids comes from mixing your carotenoids, rather than large doses of single carotenoids. Furthermore, caution should be taken, however, regarding taking carotenoids in the form of supplemented tablets. A substantial European study evaluated a large group of individuals who had a high risk of developing lung cancer (heavy smokers, previous caner of the throat). They were given carotenoid supplements in the form of alpha-tocopherol and beta carotene. The trial actually, showed an elevated risk of lung and prostate cancer! In another laboratory experiment, this time in rats with cancer, half had their diet supplemented with large quantities of dried tomato powder (the nearest thing to natural tomatoes which rats would eat) and the other half where given a supplement of pure lycopene. After only a few weeks there was a measurable and statistically significant difference in the growth rate of their tumour in favour of the powder. Another large dietary prevention study combined beta-carotene with retinol (Vitamin A), and showed complex but fascinating results which probably provide the best insight to date on the whole supplementation story. In this eloquent study, individuals had blood tests at the start and stored for later analysis. When the outcomes were later scrutinised people who started the trial with naturally low blood levels of beta-carotene had lower levels of prostate cancer after years of beta-carotene supplementation. Those people who had high initial levels beta-carotene following supplementation ended up with a higher risk of cancer particularly prostate. This trial clearly shows that too much of a single anti-oxidant can therefore be harmful but correcting a natural or acquired deficit can be helpful.

Taking antioxidants within natural foods therefore has a number of advantages. Firstly, it’s unlikely that a natural food will have very high concentrations of a single chemical, but will have a range of anti-oxidants and other beneficial agents. Secondly, in its natural form, the body is better equipped to avoid absorption of a chemical it doesn’t need or excrete ones we have too much of, avoiding excessive blood levels. Third, foods with naturally high levels of anti-oxidants are often healthy for many other reasons. They usually are high in fibre, vitamins and others substances we know about and maybe others yet to be discovered. Forth, food is cheaper than supplements which can be a financial strain on many families.

What foods contain carotenoids?    A healthy Mediterranean diet or more specifically from the following foods:- 

  • Beta-carotene (carrots, peaches, apricots, spinach and cantaloupe)
  • Alpha-carotene (carrots and pumpkins)
  • Cryptoxanthin (oranges, papaya, peaches and tangerines)
  • Lycopene (tomatoes, chilli, watermelon and pink grapefruit)
  • Lutein & Zeaxanthin (spinach, red pepper, peas, kale, broccoli and celery)

Trace metals & salts: Manganese, copper and zinc are dietary trace elements, classified as antioxidants because they are essential for the production of superoxide dismutase (SOD) and selenium is also essential for glutathione peroxidase. Together with catalase, these form enzymatic defence against carcinogenic free oxygen radical reduction metabolites (see chapter xx). These three enzymes are responsible for the end stage of mopping up of the free radicals before they have time to damage the DNA. It has been postulated that intensive farming food techniques and food processing may reduce these trace metals in our diet.  Research from animal studies has shown that there is an increased risk of cancer in the presence of cooper, manganese, seleniun or zinc deficiencies particularly under conditions of high carcinogenic attack where more SOD is needed. Zinc is abundant in many food sources and tends to accumulate more in the prostate, and one laboratory study suggested that this may offer some protection against prostate cancer cell growth.  

Zinc in excess, as you can image, is likely to be harmful. This was highlighted in the Health Professionals Follow-Up Study (HPFS). In this study, 50,000 health professionals were recruited between 1986 and 2002, from several medical fields. They were required to provide information on their eating, smoking and drinking habits, including the type of alcohol they preferred and supplements they took. During the study, 3,348 cases of prostate cancer were diagnosed. Further analysis of the diet and type of cancer showed that men who took normal amounts of zinc had the normal incidence of prostate cancer but those who took supplemental zinc at levels of more than 100mg/day or for long durations were more than twice as likely to develop advanced prostate cancer.

Selenium has been shown to slow the progression of cancer cells when it was added to their culture medium in the laboratory. This was affect was also independent of the enzymatic SOD pathway, indicating that selenium on its own may have a direct anticancer effect. In humans two large studies in 1980 and 1990 showed that a low selenium status was associated with an increased risk of developing cancer. They also showed that in patients with selenium deficiency, the cancer they developed were more likely to be aggressive and fatal. The Harvard Health professional survey, for example, linked low selenium status (measured on toenail clippings!) with higher rates of aggressive prostate cancer. Both Finish and Taiwanese studies have linked blood lower levels of selenium with higher rates of lung and a liver cancer called Hepatocellular carcinoma (HCC). In China, where the incidence of HCC is high, the inhabitants of one village were supplemented with sodium selenite whilst another 5 villages were given simple salt. After 6 years, involving over 130,000 people, there was a 35% reduction in the HCC rate in the selenium supplemented village but no change in the others.

These data prompted the designed and initiation of an excellent double-blind randomised trial in the USA called the Nutritional Prevention Study. It recruited 1312 individuals with a history of skin cancer and prescribed either placebo or 220 micrograms of selenium a day. The primary aim (end point), was to see if dietary selenium supplementation could reduce the risk of recurrent skin cancer. There was no difference in the number of skin cancers between the selenium or placebo group. However, when the data was analysised in more detail, a significantly lower level of lung, bowel and prostate cancer was seen in the selenium group and this lived up to robust statistical evaluation. Several large ongoing prostate prevention studies including the SELECT study are now underway across the world to try and confirm these findings and fine tune the optimal selenium dose required. Many suspect however that the people who would benefit from selenium supplements are those with a dietary deficiency in the first place for example those living in area with low soil levels.

Calcium. Four prospective cohort studies, relating to calcium and prostate cancer, have been published. Two recommended a mean calcium intake between 1330-1840mg/day and showed no benefit or risk or associated risk. Two others, one involving 86,404 men in the CP II Nutrition cohort, with mean intake of >2000mg/day from food and supplements, actually showed a significantly higher rate of prostate cancer. Five of nine further questionnaire surveys associated high intake of dairy food with an increased risk of prostate & breast cancer but interpretation of these was complicated the fact that high diary was associated with high fat intake. The detrimental effect of excessive calcium is thought to lay in the finding that high dietary calcium can reduce blood and cellular vitamin D levels. As will be described in more detail below Vitamin D has demonstrated anticancer effects via its anti-proliferative properties and these benefits are therefore lost with calcium excess.

Advice on healthy dietary mineral intake

Selenium - recommended 60-75mcg/day. (No more than 200mcg/day). Zinc (no more than 11mg zinc per day.:

  • Caution should be taken with uncontrolled dietary supplements dietary sources include;

  • Brazil nuts, sardines, prawns, shellfish, crab and crab liver are good sources.

  • Wheat can be a good sources but it depends on were it was grown, USA wheat is relatively high in selenium but the same cannot be said for European varieties because of the low levels in most European soils.

  • Oily fish contains selenium but this may well be bound to the mercury and made inert.

  • Meat and other cereals, contain small  quantities. As for all founds its best not to overdose on one particular type – a handful of brazil nuts a day is likely to be helpful particular in areas of the world with low selenium in the soil but any more than this could concentrate.

 Calcium - recommended dietary calcium intakes 1000mg/day for women and 800mg / day for men

  • Calcium supplements on their own may well have a detrimental effect on cancer but combined with Vitamin D are useful and also treat and prevent bone loss.

  • Foods high in calcium include regular and slimmed milk, cheese (particularly cheddar), low fat and regular yogurt, canned fish with bones (sardines, salmon) and spinach.

  • Soya products often have calcium added. Low quantities are also present in salads, fruit and vegetables.

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