It may be a cliché that you are what you eat, but there are few areas where it rings truer than when it comes to cancer development and prevention. The links between diet and cancer were highlighted more than 30 years ago when Professors Richard Doll and Richard Peto reported that more than a third of all cancers might be attributable to dietary factors. Since then it has become clear that diet plays a role in preventing as well as increasing the risk of a whole range of cancers - for example research suggests that around 90% of colorectal cancers may be preventable through changes in diet. More recently, the distinguished nutritional biochemist Professor T Colin Campbell of Cornell University has shown that the right diet prevents many common cancers, and that diet may also be the key to turning on and turning off existing cancers.

Numerous scientific studies have shown not only that the risk of developing cancer is related to your diet, but that people who eat more animal foods are more vulnerable to a range of cancers than those whose diet contains more fruit, vegetables and other plant-based foods. There is in fact a direct relationship between the incidences of many cancers and the amount of animal-based food that we eat, whereas there is no relationship with the amount of plant-based food we consume.

Recent studies link a wide range of cancers, including colorectal, oesophageal, bladder, breast, prostate, gastric, ovarian , kidney and even pancreatic cancer, to high intakes of animal-foods, especially processed meat and dairy. High-fat dairy was strongly implicated in two types of oesophageal cancer. Recent research found that women with the most plant-based diets were 3.5 times less likely to be diagnosed with precancerous cervical lesions than women whose diets contained more meat, fat and junk food. The same study also showed that a plant-based diet lowers the risk of head and neck and bladder cancer as well as pre-cancerous conditions such as colorectal adenomas.

The food revolution

Today's Western diet is so different from the one we evolved to eat that our ancestors would hardly recognise it. For tens of millions of years our ancestors lived in small groups foraging for edible tubers, leafy plants, nuts, seeds, fruit and berries as well as hunting - and occasionally catching - animals to eat. Our closest living relatives, the great apes and chimpanzees, with which we share 99% of our DNA, are predominantly herbivorous. Human beings living at low latitudes have eaten predominantly plant-based diets since prehistoric times. It was mainly as early humans migrated north that the amount of animal protein in the diet increased, a pattern that remains to this day.

The latest UK national diet and nutrition survey shows that our diet is now dominated by refined cereals, (industrialised) meat, dairy and other animal products, with far less fruit and vegetables than our bodies were designed for. Most dramatic of all has been the increase in fast and convenience foods and the use of additives. An estimated 3,800 chemicals - or more - are now used as additives to flavour, colour or preserve such foods and the average person in the West now eats more than 4kg of food additives a year. The book, Fast Food Nation listed more than 50 synthetic chemicals used to make the artificial strawberry flavour in milk shakes. On top of that, many chemical pesticides, introduced since the Second World War, have been found to be carcinogenic. We consider pesticides and other environmental carcinogens in more detail in Step 7.

The bottom line is that we are eating an unnatural diet, and it is not surprising that there is a price to pay. It is against this beleaguered nutritional background that many common cancers flourish.


How diet affects your cancer risk

It is becoming increasingly apparent that what we eat can directly, or indirectly, create conditions in which cancer can flourish, or alternatively provide protection so that cancer does not take hold.

At the most basic level what we eat provides us with the energy and vital nutrients that our bodies need to function. A diet that is rich in fruit and vegetables, for example, contains vitamins and plant chemicals that will not only help maintain a healthy immune system, they may also help protect against the DNA damage that we know can happen as a result of normal metabolism.

But the role of diet is even more complex and far-reaching. Take salt, for example. In Step 1 we outlined the role of the sodium channel in cancer cells in increasing their 'excitability' and enabling them to invade other tissues - so it follows that a high salt (sodium) diet may be significant when it comes to cancer risk.

There is also increasing evidence that diet affects the microbe population living in our intestine, known as our gut biota. Recent research on the gut micro biome (the trillions of microbes lining your small intestine along with their interacting genes) has shown that it has many important biochemical functions in the body - and when things go wrong it can lead to disease. The development of colon cancer for example, is linked closely with a high intake of red and processed meat. Now advances in sequencing technologies have given us the opportunity to study the characteristics of the human gut microbiome and the effects of what we eat - and the findings are striking. A change in diet from a low-fat, plant based diet to a high-fat, high-sugar diet, for example, has been shown to shift the structure of our gut micro biota in a single day. There is much more work to be done but understanding micro biome activity is now seen as essential to the development of future personalized healthcare.

We know that cancer development also depends on the interaction between our genes and lifestyle factors, including diet - so what you eat can actually have an impact at a genetic level. While the genes we are born with are there for life, 'bad' genes such as cancer genes do not cause problems if they are not turned on or 'expressed'. There is increasing evidence that diet is important in determining whether cancer genes are expressed or not.

The power of what we do, or do not, put into our mouths was illustrated by Dean Ornish MD, Clinical Professor of Medicine at the University of California when he showed that early stage prostate cancer could be reversed by diet and lifestyle changes. The randomised, controlled clinical trial, conducted in collaboration with world leading microbiologist Craig T Venter, found that after only three months on a plant-based diet, over 450 cancer genes had been down-regulated and 48 protective genes had been up-regulated. In other words genes linked to prostate (and breast) cancer had been turned off and protective genes turned on. Patients with otherwise untreated early prostate cancer were put into remission. The diet Professor Ornish used was a predominantly vegan diet, similar to the one we have outlined in this chapter.

Another recent intervention study showed that eating more fruit, vegetables and fibre and less saturated fat could help maintain lower levels of PSA (the protein which is an indicator of prostate cancer) in men who had had recurrent prostate cancer. Intervention studies using diet to treat other cancers are now underway.

So cutting out the wrong foods and eating the right ones could have the potential to help stop cancer in its tracks by depriving the early stage cancer cells - the initiated cells that we learned about in Step 1 - of the conditions they need to grow. As we learnt in Step 1, cancer cells are our own cells that have sustained damage to their DNA, particularly the 'cell cycle genes' which control cell reproduction. This damage makes them hypersensitive to tiny chemical messenger proteins called 'growth factors' that circulate in our blood. Whereas normal cells are unaffected, as another set of proteins tells them to stop, this doesn't work for cancer cells. They 'think' they have been told to go into their reproductive cycle and hence can grow out of control.

Many scientists now believe that initiated cells are formed throughout our lives but most do not develop into active cancers. It can help to think of them as seeds that can develop into cancer only if they are given water and fertiliser. The fertiliser all cancer cells need are growth-factor proteins and, in the case of hormone-dependent cancers such as breast or prostate cancer, animal hormones such as oestrogen or testosterone. This is particularly true of cancers of affluence in which the modern Western diet appears to be an important factor and to cancers of poverty, which include virus-induced cancers such as those caused by hepatitis.

Conventional medicine attacks and kills cancer cells, although some that are resistant to treatment can survive. But what if, as well as attacking the cancer cells directly, you can also change the environment within the body, by depriving it of the 'fertiliser' cancer cells need and by making it more hostile to cancer? It is rather like having a persistent weed in your garden. Although you attack it by digging it up, burning it and applying pesticides, it keeps coming back. But if the weed needs acid conditions and certain chemicals to grow and spread - by making the soil alkaline and cutting off the supply of chemicals the weed can no longer flourish and will die.

That is precisely what our ten step nutritional programme aims to do to cancer cells. The programme we have outlined below is predominantly vegan. We recognise that the idea of switching to a fully vegan diet may feel daunting for some people - if you don't want to become fully vegan keep meat, fish and especially dairy foods to an minimum. Professor Dean Ornish suggests that if you are currently healthy but want to follow a diet that protects against cancer you should increase the amount of vegetables and fruit you eat, making sure you include plenty of beans, soya and other sources of plant protein.. Harvard University is now recommending a similar diet. Try it. You might be surprised at how well and how full of energy you will feel and how enjoyable this sort of diet can be.

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