More than one in three people in the UK will develop some form of cancer during their lifetime (NHS Choices, 2012u). Around 325,000 people were diagnosed with cancer in 2010 in the UK, that’s around 890 people every day. Cancer causes more than one in four of all deaths in the UK. In 2010 around 430 people died from cancer every day; that is one person every four minutes (Cancer Research UK, 2013). The four most common cancers in the UK are breast, prostate, lung and colorectal (bowel) cancer. The data shows that while incidence rates have increased over previous years, mortality rates have fallen. So more people are getting cancer, but less are dying from it. The net result is that mortality from cancer over the last 50 years has remained fairly constant. This is very worrying when you consider the vast improvement in both cancer diagnosis techniques and cancer treatment methods. It means that as even more people are getting cancer, the medical profession are running, just to stand still. It is predicted that by 2020 almost one in two people (47 per cent) will get cancer in their lifetime (Macmillan Cancer Support, 2013). This poses a huge challenge for the NHS and for society.
Up to 40 per cent of cancers in the UK could be prevented by lifestyle changes (Parkin et al., 2010). Most people now recognise that smoking is the biggest single preventable risk factor for cancer. Lung cancer is the UK’s biggest cancer killer, causing one in four of all deaths from cancer. Nearly 35,000 people die from lung cancer in the UK every year (NHS Choices, 2013a). Smoking also increases the risk of many other types of cancer, including cancers of the: mouth, pharynx (behind the nose), larynx (voice box), oesophagus, stomach, pancreas, liver, cervix, kidney and bladder. Stopping smoking, even when middle-aged, can dramatically reduce the risk of developing cancer.
However, it is less well known that a poor diet is the second largest preventable risk factor for cancer, coming close behind smoking. Research shows that nutrition plays a major role in cancer (Donaldson, 2004). Indeed a poor diet may be responsible for up to a third of all cancer deaths. Evidence from migration studies from the 1980’s shows that plantbased diets can protect against cancer, while typical Western diets, rich in animal foods, sugar and highly processed food products, can increase the risk. Indeed, a significant body of evidence now shows that a plant-based diet, containing less saturated animal fats, cholesterol, animal protein, sugar, salt and processed foods can lower the risk of some cancers and that a diet rich in saturated animal fats, cholesterol, animal protein, sugar, salt and processed foods can increase the risk of certain cancers. Diet has now been linked to numerous types of cancer including cancer of the: bowel, stomach, breast, lung, prostate, pancreas, oesophagus and bladder (Cancer Research UK, 2011).
The link between red and processed meat and cancer is now well-established. In 2007, a review by a team of experts convened by the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) concluded that red and processed meats increase the risk of some cancers and that diets rich in plant foods decrease the risk of many types of cancer (WCRF/AICR, 2007). They specified the beneficial effects of fibre, fruits, vegetables, beans, peas and pulses (including soya foods) and whole grains Their recommendation was as follows: To reduce your cancer risk, eat no more than 500 grams (cooked weight) per week of red meat, like beef, pork and lamb, and avoid processed meats such as ham, bacon, salami, hot dogs and some sausages. This was headline news; telling people to avoid all processed meats. The link between red and processed meat and cancer was further supported by a large scale study of over half a million people aged 50 to 71 years who were followed for 10 years (Sinha et al., 2009). They too found that red and processed meat intakes were associated with an increased risk of death from cancer (as well as cardiovascular disease).
The European Prospective Investigation into Cancer and Nutrition (EPIC) study is a Europe-wide prospective cohort study of the relationships between diet and cancer. With over half a million participants, it is the largest study of diet and disease to be undertaken. EPIC is coordinated by the International Agency for Research on Cancer (IARC), part of the World Health Organization (WHO). 521,457 healthy adults (mostly aged 35-70), were recruited from 23 centres in 10 European countries: Denmark, France, Germany, Greece, Italy, The Netherlands, Norway, Spain, Sweden and the UK. One UK centre (Oxford) recruited 27,000 vegetarians and vegans; this subgroup forms the largest study of this dietary group.
Strong evidence that vegetarian diets are associated with reduced cancer risk was provided by a recent large scale study from the Oxford Vegetarian Study and the EPIC-Oxford group. Prospective studies follow groups of people over time. Generally these people are alike in many but not all ways (for example, young women who smoke and young women who do not). The prospective cohort study will then look for a link between their behaviour and a particular outcome (such as lung cancer). In this study, 61,566 British adults were separated into three diet groups: meat-eaters (32,403), fish-eaters (8,562) and vegetarians (20,601). After 12 years, 3,350 had been diagnosed with cancer (2,204 meat-eaters, 317 fish-eaters and 829 vegetarians). Total cancer incidence was significantly lower among both fish-eaters and vegetarians (18 and 12 per cent lower respectively) than among meat-eaters. Interestingly, there were vegans in this cohort, but there were too few to be informative (Key et al., 2009). However, in a follow-on study, they determined a significant statistic for the vegan group; total cancer incidence was again lower in fish-eaters and vegetarians (12 and 11 per cent respectively) but was 19 per cent lower in vegans compared with meat-eaters (Key et al., 2014).
Another large scale study (over 500,000 participants) from the EPIC group found that increasing the intake of fruit and vegetables by 200 grams per day lowered the risk of cancer (albeit by a few per cent). The authors cautioned against over interpreting these results when making dietary recommendations for cancer risk reduction because the magnitude of the effect was relatively small (Boffetta et al., 2010). Both the vegetarian and non-vegetarian people in the EPIC-Oxford Study were shown to have overall lower cancer rates than the general population of the UK. It was noted that the meat intake of the meat-eaters group was lower than intakes reported in the National Diet and Nutrition Survey for the UK (Key et al., 2009a). It seems likely that the meat-eaters in this health conscious study group are not typical of the wider meat-eating population. If you compared cancer rates between the average UK meat-eater with vegetarians and vegans, the difference between the two may be even greater.
The extent to which a vegetarian diet lowers the risk of cancer depends largely on what is in the diet. The diets of some Western vegetarians may have a similar macronutrient and micronutrient profile to that of a typical Western style diet. In other words, a vegetarian junk food diet! A wide variation exists in what Western vegetarians eat. The diet may include very large or very small amounts of: whole grain foods, raw foods, highly processed foods, sugary sweet foods, fatty foods and crucially may vary widely with respect to eggs, cheese, cream, butter and other dairy products. This may go some way to explain why there are discrepancies in the results of some studies looking at cancer and diet. This (coupled to the ‘health conscious’ character of the meat-eaters in the EPIC group) may account for why a review of five prospective studies showed no large differences in cancer mortality between vegetarians and non-vegetarians (Key et al., 1999). In another example from the EPIC group, they found that British vegetarians had a similar risk of colorectal cancer as non-vegetarians (Fraser et al., 2009). Whereas other studies provide convincing evidence that plant-based diets are protective against colorectal cancer (WCRF/AICR, 2007). It is likely that using ‘vegetarian’ as a single dietary label in research is probably inadequate and this group needs to be divided into more descriptive subtypes to include vegans. However, taken together, the evidence suggests that vegetarian diets are a useful strategy for reducing cancer risk (Lanou and Svenson, 2010).
It has been suggested that animal protein increases the risk of cancer. In Professor T. Colin Campbell’s extensive China Study (one of the largest studies in the world on the effects of diet on health) a startling observation was made. Based on previous work and his own studies, Campbell saw a direct link between dietary protein intake and cancer; the more protein in the diet, the higher the risk of certain cancers, such as liver cancer. But this was not all protein, just animal protein. Campbell decided to look at the relationships between animal protein intake and the incidence of cancer in different cultures.
Colorectal cancer is the fourth most common cancer in the world; it is the second most common in the US. Campbell noted that while North America, Europe, Australia and wealthier Asian countries (such as Japan and Singapore) had relatively high rates of colorectal cancer, Africa, Asia and most of Central and South America had much lower rates. For example, Campbell noted that the Czech Republic had a death rate of 34.19 per 100,000 males, while in Bangladesh the figure was just 0.63 per 100,000 males (Campbell and Campbell, 2005). Campbell is not alone in revealing the enormous differences in the incidences of certain cancers between countries. The International Agency for Research on Cancer (IARC) provides startling figures comparing the incidence of breast cancer and prostate cancer in England and Wales to that in rural China. In 1997, in England and Wales, the IARC reported the incidence rate of breast cancer in women was 68.8 per 100,000 compared to just 11.2 per 100,000 in rural China. Similarly the incidence of prostate cancer in men in England and Wales was 28.0 per 100,000 compared to just 0.5 per 100,000 in rural China (IARC, 1997).
It is widely acknowledged that the incidence of certain cancers is much greater in some countries than others, what intrigued Campbell was the relationship between these cancers and dietary animal protein. Figure 4.0 shows the differences in animal protein intake between the US, the UK and rural China. In the US, over 15 per cent of total energy intake comes from protein of which 70 per cent is animal protein (Campbell and Campbell, 2005). In the UK, over 16 per cent of food energy comes from protein, and of this, 62 per cent comes from animal foods (Henderson et al., 2003). While in rural China, the figures are quite different; nine to 10 per cent of total energy comes from protein and only 10 per cent of that is from animal protein (Campbell and Campbell, 2005).
It could be argued that the difference in cancer incidence between cultures reflects genetic differences between ethnic groups rather than environmental (dietary) effects. However, as stated above, migrant studies have shown that as people move from a lowcancer risk area to a high-cancer risk area, they assume an increased risk within two generations (WCRF/AICR, 1997). Therefore these vast differences in cancer rates must be largely attributable to environmental factors such as diet and lifestyle. Campbell concluded that animal-based foods are linked to an increased cancer risk whereas a whole grain plant-based diet including fibre and antioxidants is linked to lower rates of cancer (Campbell and Campbell, 2005). One possible mechanism for this may be the different composition of animal and plant proteins.
Plant proteins contain a different balance of amino acids than animal proteins. More specifically, plant proteins contain less of the essential amino acids methionine and lysine than animal protein and more of the non-essential amino acids arginine, glycine, alanine and serine. It has been suggested that consuming mostly a plant-based diet has a knock-on effect of limiting the biological activity of certain chemical substances involved in cancer development and that a sufficient consumption of plant proteins has a protective role against cancer (Krajcovicova- Kudlackova, 2005). So a vegetarian diet is a healthier option, not just because it excludes meat and other animal foods but because of the range of beneficial, protective factors present. Vegetarian diets contain less saturated fats and more of the good fats (omega-3 and omega-6 unsaturated fatty acids), more complex carbohydrates, more fibre and more vitamins, minerals and antioxidants. These factors help to explain the reduced risk of cancer in vegetarians.
Increasing your fruit and vegetable consumption is considered the second most effective strategy to reduce the risk of cancer (after stopping smoking). Indeed, one of the most important messages of modern nutrition research is that a diet rich in fruits and vegetables protects not only against cancer, but against many other diseases too including heart disease and diabetes (Donaldson, 2004). In 2003 the UK Department of Health launched its 5-a-day campaign, encouraging people to eat more fruit and vegetables. The campaign is based on advice from the World Health Organization, which recommends eating a minimum of 400g of fruit and vegetables a day to lower the risk of serious health problems, such as heart disease, stroke, type 2 diabetes and obesity. In 2012 the National Diet and Nutrition Survey showed that despite the campaign, adults are still only eating four portions a day and children are eating just three or less.
Further to this, there is an increasing body of evidence linking the consumption of cow’s milk to certain cancers. One of the reasons for this may be the increasing levels of hormones and other bioactive compounds present in the milk that result from intensive farming practices (taking milk from pregnant cows). In other words, in an effort to increase milk production, the dairy industry has intensified farming techniques to such a high level that between 75 per cent and 90 per cent of marketed milk and milk products are derived from pregnant cows (Danby, 2005). (See The undesirable components of milk and dairy products).
There are a number of other important factors that can contribute to the development of cancer, including obesity (breast and endometrial cancer), alcohol (mouth, throat, liver and breast cancer), sunlight (skin cancer), radon (lung cancer) and physical activity can protect against some cancers (colorectal).
There are more than 200 different types of cancer, but just four of them (breast, lung, colorectal and prostate) account for over half (54 per cent) of all new cases (Cancer Research UK, 2012). The role of cow’s milk and dairy products in breast, colorectal, ovarian and prostate cancer is discussed in more detail.