Prostate cancer

Summary

Like breast cancer, prostate cancer rates are rising and one in eight men in the UK will get prostate cancer at some point in their lives. Rates vary widely around the world but as the Western diet spreads, so does prostate cancer.

Meat (particularly red, processed and well-done meat), is linked to a higher risk of prostate cancer. A US study found that during a week, three servings of red meat, one and a half servings of processed meat, one serving of grilled red meat or one serving of well-done red meat were each associated with a 50 per cent increased risk of advanced prostate cancer. 

There is a link with poultry too, especially chicken and turkey with skin as well as hot dogs and sandwiches made with chicken and turkey. In the CaPSURE study, men eating the most poultry with skin had more than double the risk of prostate cancer progression than those eating the least. The PCRM found that diets high in saturated fat are associated with a threefold risk of cancer progression and death. Disease progression was slower in men who ate flaxseed and lycopene-containing foods like tomatoes.   

The Prostate Cancer Lifestyle Trial showed that men with early-stage prostate cancer might be able to avoid or delay conventional treatment by adopting a low-fat, vegan diet. This sort of dietary advice on how a vegan diet, high in fibre and phytonutrients and low in fat and saturated fat, may prevent and slow prostate cancer, could provide men with a focus for action and a means of regaining control. 

Prostate cancer is the most common cancer in men. Across the UK, over 47,000 men are diagnosed with it every year – 130 men every day. Prostate cancer incidence rates have increased by 155 per cent in men in the UK since the late 1970s. Some of this may be down to increased testing but the fact remains that in the UK, about one in eight men will get prostate cancer at some point in their lives. 

Prostate cancer incidence varies more than 25-fold worldwide; the pattern is similar to that of breast cancer incidence with the highest rates seen in Australia, New Zealand, North America, Western and Northern Europe, where the age-standardised rate is around 100 men per 100,000 (GLOBOCAN, 2012).  Incidence rates are also relatively high in some less affluent regions such as the Caribbean (79.8), Southern Africa (61.8) and South America (60.1), but remain low in Asian populations with estimated rates of 10.5 in Eastern Asia and 4.5 in South-Central Asia.

This leading cause of cancer death in most developed countries is now emerging as a major public health problem in developing countries too (Jemal et al., 2011). Prostate cancer incidence rates have been rapidly increasing in China, Korea, Japan and Singapore during the last few decades (Zhang et al., 2012). This increase is thought to be caused by the gradual change towards the Westernised diet with high intakes of energy, animal fat and meat and a low intake of fibre (Gathirua-Mwangi and Zhang, 2014).

Migrant studies provide further evidence that diet plays a role in prostate cancer as remarkable increases in this disease have been observed among men who move from East Asia to North America (Gathirua-Mwangi and Zhang, 2014). High consumption of meat (particularly red, processed and well-done meat), is associated with an increased risk of prostate cancer (John et al., 2011). A review of 46 studies found that saturated fat, well-done meat and calcium are all consistently linked to an increased risk for advanced prostate cancer (Gathiru-Mwang and Zhang, 2014). Interestingly, calcium from dairy products, but not calcium from other foods was associated with the risk of prostate cancer (Allen et al., 2008).  

In a US study of men from the Greater San Francisco Bay Area, weekly consumption of three or more servings of red meat, one and a half or more servings of processed meat, one or more serving of grilled red meat and one or more serving of well-done red meat were each associated with a 50 per cent increased risk of developing advanced prostate cancer (John et al., 2011).

In this study of men from the Greater San Francisco Bay Area, although the increased prostate cancer risk was associated with grilled and well-done red meat, they found no consistent associations with HCAs (except for a possible link with advanced disease and PhIP). However, more than 15 different HCAs are known to accumulate in cooked meat, yet usually only three (PhIP, MeIQx and DiMeIQx) are measured and compounds formed at lower concentrations, which are not measured or not-yet identified, may play a role in prostate cancer (Joshi et al., 2012). While this study also found no consistent association with BaP (the most abundant PAH) the authors said that they couldn’t exclude the possibility that other PAHs formed during cooking may underlie the link between grilled red meat and prostate cancer. 

Another study, looking at 2,770 cases of prostate cancer among 26,030 men did find a positive association between PhIP from red meat and prostate cancer, particularly high-grade (fast-growing) and possibly also advanced prostate cancer (Rohrmann et al., 2015). However, they noted that while PhIP intake from red but not from white meat was linked with prostate cancer, PhIP intake from white meat is twice as high as that from red meat. This, they said, argues against PhIP (or HCAs in general) as the factor responsible for the link between meat and prostate cancer and suggests that some other mutagenic compounds arising from meat may be the causal factor. More research is required to fully-elucidate the underlying mechanisms.

The research on how diet may affect progression of prostate cancer after diagnosis is of great interest given the large numbers of men diagnosed with this disease. Researchers from the Physicians Committee for Responsible Medicine (PCRM) reviewed eight observational studies and 17 intervention studies on the effect of diet on prostate cancer and found that diets high in saturated fat are associated with a threefold higher risk of cancer progression and death, compared with a diet low in saturated fat (Berkow et al., 2007). This review revealed a slowing of disease progression in prostate cancer patients consuming flaxseed and lycopene-containing foods (tomatoes are a rich source of lycopene). The authors concluded that plant-based diets – high in fibre and phytonutrients and low in fat and saturated fat – favourably influence health outcomes for prostate cancer patients.

Another study looking at how diet may affect disease progression found that two and a half eggs per week increased the risk of lethal prostate cancer by 81 per cent compared to less than half an egg per week (Richman et al., 2011). They also found a link between poultry and processed meat and progression to lethal prostate cancer, but these associations were of borderline statistical significance. The association with poultry appeared to be driven by poultry and poultry products with skin (chicken or turkey with skin, chicken or turkey hot dogs and chicken or turkey sandwiches). The authors said they had limited power to examine individual poultry items due to low consumption of these foods in their study population. Those eating three and a half servings a week of poultry products were put in the highest consumer group; many people eat a lot more chicken than that. Also, the men who ate the most poultry in this study engaged in more vigorous activity, were less likely to be smokers and consumed less red meat, dairy and coffee than men who ate the least poultry. These factors may have contributed somewhat to masking the harmful effects of poultry in this relatively healthier-living group of low-consumers.  

The relationship between eating poultry with skin after diagnosis and clinical outcomes (or disease progression) in men with prostate cancer has been examined before. In the CaPSURE study, men who ate the most poultry with skin had more than double the risk of prostate cancer progression compared with men who ate the least (Richman et al., 2010).

The Prostate Cancer Lifestyle Trial was a one-year randomised controlled clinical trial of 93 patients with early-stage prostate cancer who had chosen not to undergo conventional treatment (Ornish et al., 2005). This was a unique opportunity to observe the effects of diet and lifestyle changes without the confounding effects of radiation or surgery. The patients in the experimental group followed a vegan diet consisting of fruits, vegetables, wholegrains and pulses including soya. They also exercised, practised stress management and attended group support sessions. The control patients received the usual care. After one year, none of the vegan group had required conventional treatment but six control patients had because their disease had progressed. Prostate-specific antigen (PSA) fell four per cent in the vegan group but went up six per cent in the control group. Although the size of these changes was modest, the direction of change is important as an increase in PSA indicates disease progression. In a second test, prostate cancer cells in vitro were exposed to blood serum from both groups to see if it stimulated or decreased prostate cancer cell growth. Serum from the vegan group inhibited growth almost eight times more than serum from the control group (70 versus nine per cent), suggesting that comprehensive lifestyle changes could affect tumour growth.

In a subsequent study, after two years, just two (five per cent) of the 43 vegan patients had undergone conventional treatment but 13 (almost a third) of the 49 control patients had. Dr Dean Ornish, clinical professor of medicine and founder and president of the Preventive Medicine Research Institute, concluded that patients with early-stage prostate cancer might be able to avoid or delay conventional treatment for at least two years by making changes in their diet and lifestyle (Frattaroli et al., 2008).

Taken together, this research provides further evidence that poultry, red and processed meat are associated with increased risk of prostate cancer. While the exact mechanism underlying the links between meat and prostate cancer remain unclear, the association remains firmly established. Research shows that if health professionals can offer qualified, general advice about diet, this may provide men with a focus for action and a means of regaining control (Kassianos et al., 2015).

The links between meat and cancer explained

Several explanations have been suggested for the link between red meat and prostate cancer. HCAs formed when meat is cooked at high temperatures may account for the link between poultry after diagnosis and risk of lethal prostate cancer (Richman et al., 2010). HCAs form DNA adducts (this is when DNA becomes bound to a cancer-causing chemical) and so increase the occurrence of numerous cancers including prostate cancer (Richman et al., 2011). Chicken is a primary source of HCAs in the typical Western diet and fried, roast and grilled chicken can contain particularly high amounts of HCAs.

Another obvious culprit is the saturated fat in meat, which has long been proposed as a risk factor. Total and saturated fat intake have both been positively associated with PSA levels (this is a protein produced by the prostate gland used to assess disease progression), increased risk of prostate cancer and aggressive prostate cancer, while saturated fat intake has been associated with fatal prostate cancer (Bishop et al., 2015).

However, results of some studies of dietary fat and prostate cancer are inconsistent, some having a link with red meat but not fat. Other explanations include the presence of haem iron in red meat, which may catalyse oxidative reactions. Finally, an association between prostate cancer and meat intake may be due to potent chemical carcinogens generated during cooking and processing of red meat and poultry, such as NOCs, HCAs and PAHs. The prostate gland is able to metabolise these chemicals into activated carcinogens (Joshi et al., 2012).

The telomere study

In a later study, Ornish focussed on telomeres, stretches of DNA that protect the ends of our chromosomes rather like the plastic caps that prevent shoelaces from unravelling (Ornish et al., 2013). Every time a cell divides, telomeres become shorter. Once they reach a critically short length, the cell stops dividing and dies. As more body cells are lost, signs of ageing begin to appear, which may be followed by age-related diseases such as cancer, stroke, heart disease, vascular dementia, obesity, osteoporosis and diabetes.

Dr Ornish worked alongside Elizabeth Blackburn, who won the 2009 Nobel Prize in Physiology or Medicine for her discovery of telomerase, the enzyme that replenishes telomeres. In this study, as before, one group followed Ornish’s lifestyle changes, the other group carried on as usual. They measured telomere length at the beginning of their study and again after five years. Among the men with low-risk prostate cancer who made comprehensive lifestyle changes (vegan diet, exercise, stress management and support group), telomere length increased significantly by an average of 10 per cent. Telomere length decreased by an average of three per cent in the control group.

This study suggests yet another possible mechanism by which lifestyle changes, avoiding meat and dairy, might help combat prostate cancer and other age-related diseases. Ornish said: “The implications of this relatively small pilot study may go beyond men with prostate cancer. If validated by large-scale randomised controlled trials, these comprehensive lifestyle changes may significantly reduce the risk of a wide variety of diseases and premature mortality”.

Despite all this evidence, advice from the NHS on the links between diet and prostate cancer remains sparse.

The data linking the consumption of poultry, red and processed meat to prostate cancer provides a convincing argument for eliminating meat (and all animal foods) from the diet while increasing the intake of wholegrain foods, pulses (including soya), fruit and vegetables, nuts and seeds.