Cancer

Summary

In the UK, one in two people born after 1960 will be diagnosed with cancer during their lifetime. Just four types of cancer (breast, prostate, lung and bowel) make up more than half of all cancers. Migrant studies show that lifestyle and diet play a much larger role than genes. After smoking, poor diet is the most important avoidable cause and people who eat meat have a higher risk.

The US NIH-AARP Diet and Health Study found people who eat the most red meat had a 20-60 per cent higher risk for oesophageal, bowel, liver and lung cancer. Those eating the most processed meat had a 16-20 per cent higher risk for bowel and lung cancer.

Vegetarians and vegans have a lower risk of cancer than meat-eaters. In the UK, vegetarians have an 11 per cent lower risk and vegans 19 per cent lower. The AHS-2 had similar results; vegetarians had an eight per cent lower risk and vegans 16 per cent lower. Vegan women had 34 per cent fewer female-specific cancers.

A study of cancer in 157 countries found high intakes of animal products linked to higher rates of cancers of the breast, kidney, pancreas, prostate and thyroid. Another study found that people eating high levels of animal (but not plant) protein are over four times more likely to die of cancer.

Chicken is not a healthy option; modern supermarket chickens contain more fat than protein, much of it saturated.  High-saturated fat intake increases the risk of breast, prostate and bowel cancer as well as heart disease and diabetes while animal protein increases IGF-1 levels linked to bowel and lung cancer. Haem iron from meat generates free radicals and induces oxidative stress. Chicken also contains higher levels than red meat of the carcinogenic compound PhIP.

In 2015, the WHO announced that processed meat does cause cancer and that red meat probably does too. Just 50g of processed meat (less than two slices of bacon) a day increases the risk of bowel cancer by 18 per cent. Current guidelines need to be amended to reflect the now indisputable link between meat and cancer. Cigarettes carry government health warnings, why shouldn’t bacon and chicken nuggets? 

Every year, there are more than 10 million new cases of cancer around the world; they are not spread evenly across the globe (Cross et al., 2007). In 2012, the age-standardised incidence rate (how many out of every 100,000 people will have the disease in a given year) for all cancers for men and women across the globe was 182 people per 100,000. In the UK, the figure was 273 per 100,000 (GLOBOCAN, 2012). For men, the rate varied almost seven-fold from 57 per 100,000 in Niger in Western Africa to 374 per 100,000 in Australia, where prostate cancer represents a significant proportion. Variation among women was nearly five-fold, from 70 per 100,000 in the Gambia to 328 per 100,000 in Denmark, where high rates of breast cancer occur. Denmark has been called the cancer capital as the highest cancer rate for men and women together occurs there with 338 people per 100,000 diagnosed in 2012.    

Type of cancer Percentage of total cancers
Breast* 15.6
Prostate 13.4
Lung 12.6
Bowel 11.5
Other 46.9

Table 1.0 Types of cancer registered in the UK in 2014.

Source: Office for National Statistics, 2014.

*46,085 cases in females and 332 in males.

In the UK, one in every two people born after 1960 will be diagnosed with some form of cancer during their lifetime (Ahmad et al., 2015). Although there are more than 200 different types of cancer, the four most common (breast, prostate, lung and bowel cancers) account for more than half of all cancers (NHS Choices, 2014a). Table 1.0 shows the percentages of total cancers these four most common cancers make up. 

Figure 1.0 Most common cancers in England in 2013 for women and men by percentage.

Source: Bate and Baker, 2015. 

Figure 1.0 shows that three most common cancers account for over half of all cancers in women and men. Lung and bowel cancer make up nearly a quarter of cancers in both genders, while breast and prostate cancer comprise over a quarter of cancers in women and men respectively.

Smoking is the most important preventable cause of cancer; responsible for one in four UK cancer deaths and nearly a fifth of all cancer cases (Public Health England, 2016a). Nearly half of all smokers will eventually die from smoking-related diseases. After smoking, poor diet is the most important avoidable cause of cancer.  

Countries with relatively high intakes of meat and other animal foods have higher rates of bowel, breast and prostate cancer (Key et al., 2014). Indeed, meat consumption has been recognised as a risk factor for cancer since the early 1900s. A study of cancer rates in different ethnic groups in Chicago from 1900-1907 found that heavy meat-eaters (Germans, Irish and Scandinavians) had higher rates of cancer mortality than pasta-consuming Italians and rice-eating Chinese (Grant, 2014).  

Professor T. Colin Campbell, Jacob Gould Schurman Professor Emeritus of Nutritional Biochemistry at Cornell University in the US, is the author of over 300 research papers and co-author of The China Study (Campbell and Campbell, 2005), one of America’s best-selling books about the impact of diet on our health. His legacy, the China Project, is the most comprehensive study of health and nutrition ever conducted.

The China Project was conceived in 1980-1981 when Dr Chen Junshi (Deputy Director of the Institute of Nutrition and Food Hygiene at the Chinese Academy of Preventive Medicine) visited Campbell’s laboratory at the Division of Nutritional Sciences at Cornell University in Ithaca, New York in the US. They were later joined by Professor Richard Peto from the University of Oxford in the UK and Dr. Li Junyao from the China Cancer Institute at the Chinese Academy of Medical Sciences in China. The project demonstrated important relationships between dietary patterns and cancer risk across different countries (Campbell and Junshi, 1994). It involved 65 Chinese counties and focused on their diets and health. 

Campbell and Junshi found that several major diseases including a number of different cancers as well as CVD and diabetes were all associated with affluent diets. In other words, these diseases were directly associated with the intake of meat, milk, eggs, animal fat and animal protein whilst diets high in fibre, antioxidants (mainly from fruit and vegetables) and pulses had a preventative effect. 

It had previously been suggested that animal protein increases the risk of cancer. The extensive China Study found a direct link between dietary protein intake and cancer; the more protein in the diet, the higher the risk of cancer. But this did not apply to all protein, just animal protein.   

Figure 2.0 A comparison of animal protein intake in the US, UK and rural China.

Source: Campbell and Campbell, 2005; Henderson et al., 2003.

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 animal protein and these cancers. Figure 2.0 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, migrant studies have shown that as people move from a low-cancer risk area to a high-cancer risk area, they assume an increased risk within two generations (WCRF/AICR, 2007). 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 wholegrain plant-based diet including fibre and antioxidants is linked to lower rates of cancer (Campbell and Campbell, 2005).   

Campbell has extensively pursued, for many years, the hypothesis that dietary protein enhances tumour development. Several mechanisms have been proposed including how diets rich in animal protein (meat and dairy) drive the synthesis of the growth factor insulin-like growth factor 1 (IGF-1) in the liver, which increases the risk of a range of cancers. A 2006 a study published in the American Journal of Clinical Nutrition found that compared to a typical Western diet, a low-protein, low-calorie diet was associated with significantly lower IGF-1 levels (Fontana et al., 2006). Campbell acknowledged the importance of this finding but said in his opinion the links between animal protein and IGF-1 production are only one of these countless and highly interdependent cause and effect relations that occur in human nutrition (Campbell, 2007).

Other studies have focused directly on meat. The NIH-AARP Diet and Health Study presents information on the impact of diet and lifestyle factors on risk of cancer. In 1995-1996, nearly half a million US men and women, aged 50-71, none of whom had had cancer, joined the study. They completed a questionnaire about their dietary habits with personal information such as age, weight and smoking history. During an average of seven years follow-up, 53,396 cases of cancer were reported. This information was used to identify links between the amount of meat they ate and the incidence of various cancers (Cross et al., 2007).

Results showed that those who ate the most red meat had a 20-60 per cent higher risk for oesophageal, bowel, liver and lung cancer compared to those eating the least. Those who ate the most processed meat had a 20-16 per cent higher risk for bowel and lung cancer respectively. The authors discussed different mechanisms linking meat to cancer; saturated fat, haem iron, NOCs, HCAs and PAHs. They suggested that the link between saturated fat and cancer is likely to be related to energy balance; this means too many calories. A diet high in saturated fat, leading to obesity, increases the risk of breast, prostate and bowel cancer as well as heart disease and diabetes. The increased risk of the hormone-related cancers (breast and prostate) may result from increased levels of hormones synthesised in adipose (fat) stores in the body (Gerber and Corpet, 1999).

We know that diets rich in animal protein (meat and dairy) increase IGF-1 which increases the risk of a range of cancers, including bowel and lung cancer. Iron is also thought to contribute to an increased cancer risk by generating free radicals and inducing oxidative stress (see figure 3.0). The authors of the NIH-AARP Diet and Health Study also pointed out how exposure to NOCs occurs from eating nitrite-preserved meats as well as endogenous formation in the gut, which is directly related to the haem iron content of meat. They concluded that reducing meat intake to match the lowest intake in the study group could reduce the incidence of cancer at multiple sites. As stated previously, people in the NIH-AARP study eating 53g of red meat per day could still be classed in the lowest intake group. Avoiding meat entirely would be even more effective in preventing cancer.

A UK study from the University of Oxford, looking at how different diets affects cancer risk, revealed that people who don’t eat meat have a much lower risk of getting the disease. The 15-year study was a pooled analysis of two prospective studies including 61,647 British men and women (32,491 meat-eaters, 8,612 fish-eaters, 18,298 vegetarians and 2,246 vegans) among whom there were 4,998 cases of cancer (Key et al., 2014). Results showed that compared with meat-eaters, cancer incidence was 12 per cent lower in fish-eaters, 11 per cent lower in vegetarians and 19 per cent lower in vegans. This adds to a huge body of evidence showing how meat increases the risk of cancer and other diseases (Key et al., 2014).  

The results of the US Adventist Health Study II (AHS-2) were similar, with total cancer risk significantly lower in vegetarians and vegans than in meat-eaters (Tantamango-Bartley et al., 2013). This study examined the association between diet and cancer incidence among 69,120 people among whom 2,939 cancer cases were identified during an average of four years follow-up. In this typically low-risk population, avoiding meat clearly conferred protection against cancer. Vegetarians had an eight per cent lower risk of cancer and vegans had a 16 per cent lower risk. In addition to this, vegan women experienced 34 per cent fewer female-specific cancers. The authors pointed out that the meat-eaters in AHS-2 consume much less meat than the average American. So people eating diets mainly based on meat and dairy are likely to have an even higher risk of cancer than the meat-eaters in AHS-2.

Two key studies found vegetarians have an 8-11 per cent lower risk of cancer and vegans a 16-19 per cent lower risk.

An international study comparing rates of 21 different cancers in 157 countries (reported in 87 studies in 2008), found that people who ate the most animal products had the highest rate of cancers of the breast, kidney, pancreas, prostate and thyroid (Grant, 2014). An interesting feature of this study was the time lag observed between increasing cancer rates and national dietary changes as countries adopt a more Western diet, rich in meat and dairy. Results revealed a 15-30 year lag between diet and cancer mortality; 15-27 years for bowel cancer and 20-31 years for breast cancer in Japan and 10 years for mortality rates for a number of different cancers in several Southeast Asian countries. The author said this study reiterates that animal products are an important risk factor for many types of cancer. Mechanisms discussed, linking animal products to cancer, included increased production of insulin, IGF-1 and sex hormones as well as haem iron giving rise to free radicals, oxidative stress and DNA damage. The author concluded that eating animal products is as important as smoking for increasing the incidence of all cancer types apart from lung cancer.

Even moderate intakes of animal protein are linked to a higher risk of cancer. A large cross-sectional study from the US looked at protein intake and cancer rates in 6,381 people over 18 years. Results showed those reporting a high animal protein intake had a 75 per cent higher chance of dying from all-causes during the follow-up period than people eating much less animal protein. The high-protein group were more than four times more likely to die of cancer than those in the low-protein group (Levine et al., 2014). These associations were either abolished or weakened if the source of protein was plant-based. The authors concluded that taken together, these results indicate that people aged 50-65 consuming moderate to high levels of animal protein display a major increase in their risk for cancer which could be reduced if the protein did not come from an animal source. They suggested high levels of animal protein increasing IGF-1 and possibly insulin may be responsible for the links between animal protein and cancer. These results are in agreement with recent findings on the association between meat consumption and death from all-cause, CVD and cancer (Fung et al., 2010; Pan et al., 2012).

Red and processed meat intake has long-been associated with increased risks of bowel cancer as well as several other cancers (WCRF/AICR, 2007). Several compounds either found in meat or created in it by high-temperature cooking are now known as being potential carcinogens including: NOCs, HCAs and PAHs. Haem iron and iron overload can also increase cancer risk through a range of processes including the promotion of NOC formation, increased colonic cytotoxicity and epithelial proliferation, increased oxidative stress and iron-induced hypoxia signalling (Pan et al., 2012). In other words, it contributes to compounds that can damage the cells in the colon and lead to cancer.  

Chicken and PhIPs

Poultry is a source of haem iron too and is a source of potential carcinogens particularly when cooked at high temperatures. Grilling or barbecuing meat results in the formation of HCAs and PAHs, which are potent carcinogens. PhIP is the most abundant HCA detected in the human diet. The IARC has classified PhIP as possibly carcinogenic to humans. PhIP is formed at high temperatures in a reaction between substances found in meats and sugar and depends on the method of cooking and the variety of meat and increases with the temperature and duration of cooking. Research shows that high levels of PhIP have been found in chicken that was pan-fried, oven-grilled or barbecued. In these samples, PhIP levels were much higher than amounts reported previously in red meats (Sinha et al., 1995).

WHO says meat does cause cancer

Viva!Health have been warning people about the links between meat and cancer for years and in 2015, just ahead of World Vegan Day on November 1, the World Health Organisation (WHO), one of the most-respected authorities on health, published a press release stating that processed meat does cause cancer and that red meat probably does too (WHO/IARC, 2015). This was significant because the meat industry has dismissed previous claims linking meat to cancer as ‘unscientific’ or ‘simplistic’. They are still arguing the toss but even they must now realise that they have lost the argument and are clearly trying to defend the indefensible.  

The International Agency for Research on Cancer (IARC) is the specialised cancer agency of the WHO. In October 2015, 22 scientists from ten countries met at the IARC in Lyon, France, to evaluate the carcinogenicity of the consumption of red and processed meat to decide if red and processed meats cause cancer. Their findings, published in The Lancet Oncology, hit the headlines around the world. They said that eating just 50 grams of processed meat (less than two slices of bacon) a day increases the risk of bowel cancer by 18 per cent. 

Here are three main findings from their report:

  • Overall, the Working Group classified consumption of processed meat as “carcinogenic to humans” on the basis of sufficient evidence for bowel cancer. Additionally, a positive association with the consumption of processed meat was found for stomach cancer.
  • The Working Group classified consumption of red meat as “probably carcinogenic to humans”.
  • In making this evaluation, the Working Group took into consideration all the relevant data, including the substantial epidemiological data showing a positive association between consumption of red meat and bowel cancer and the strong mechanistic evidence. Consumption of red meat was also positively associated with pancreatic and with prostate cancer.

Source: Bouvard et al., 2015.

Current guidelines need to be amended to reflect the now indisputable link between meat and cancer. Cigarettes carry government health warnings, why shouldn’t bacon? The government acknowledge the link between eating a lot of red meat and bowel cancer but they should now go further and warn people sufficiently about the risks associated with eating meat. Although much of the battle against cancer emphasises early detection and treatment, the burden of cancer in terms of both personal suffering and the financial strain on health services, will remain high unless the primary risk factors are understood and addressed.