Diet, lifestyle and prostate cancer
Introduction
The prostate is a walnut-sized gland that sits behind the bladder and in front of the rectum and secretes fluid into semen. Prostate cancer (PC) is the most common cancer in men in the UK. There are different stages of PC, all arising from a precancerous stage, which then progresses to localised cancer (within the prostate) followed by advanced cancer (outside the prostate). PC can be tracked in the blood by measuring a protein secreted by the prostate called prostate-specific antigen (PSA).
About two thirds of all PC cases occur in high income countries with a 25-fold difference in incidence between countries with high and low rates of this cancer. Individuals who migrate from low incidence countries acquire the risk of their new country. This provides us with suggestive evidence that environmental and lifestyle factors contribute to PC risk, with dietary factors also being implicated.
Dietary patterns and prostate cancer risk
In general, it is most useful to consider dietary patterns rather than individual foods when assessing cancer risk. The Western diet pattern, high in meat, refined grains and ultra-processed foods, whilst being insufficient in healthy fibre-rich plant foods is associated with a significantly higher risk of PC (around 34% higher risk) with a dose effect being apparent. In contrast, diets high in healthy plant foods are associated with a significantly lower risk of PC when compared with animal-based diets. When considering the plant-based dietary index, men who adhere to a healthy plant-based dietwith a focus on fruit, vegetables, whole grains, beans, nuts and seeds, have a significantly lower risk of PC (14% reduction) with a greater reduction (44%) for the risk of aggressive prostate cancer.
With regards to specific therapeutic diet patterns, although the Mediterranean diet is considered healthy, there does not seem to be a specific benefit for reducing prostate cancer risk. However, when specifically assessing the impact of plant-based diets, including vegetarian and vegan, there does appear to be a significant benefit for PC risk, with vegan diets consistently associated with a lower risk (up to 35% reduction). Plant-based diets are thought to be beneficial because they are higher in health promoting nutrients such as in fibre, antioxidants and anti-inflammatory compounds and low in harmful nutrients such as saturated fat, haem iron and other cancer-causing compounds.
Specific foods implicated in the development of prostate cancer
Dairy
Dairy from cows has consistently been associated with a higher risk of PC. In an analysis from the Adventist Health Study-2, which includes participants following a variety of diet patterns from omnivorous to vegan, men consuming 430g/d of dairy compared to those consuming 20.2g/d had a 27% increased risk of developing PC. The major rise in risk of PC was seen to occur between the zero intake category and second quintile of the dairy users, with the risk then remaining high but plateauing. Compared to participants consuming zero dairy, those consuming the most had a 60% increased risk. These data are supported by meta-analyses that have demonstrated a dose-dependent increase in PC risk with dairy consumption.
Why might this be? One important factor is that dairy and indeed diets high in animal products, result in higher blood levels of IGF-1. This growth factor stimulates cells to grow and is associated with an increased risk of cancer in general. Higher blood levels of IGF-1 have been associated with an increased risk of PC and other cancer. We know that the levels of IGF-1 in people that don’t consume animal products (vegans) are significantly lower than in those that do and the risk of cancer in general is lower in those following a vegan diet.
Meat
Red and processed meat consumption has been associated with an increased risk of PC in some but not all studies. One study of more than 175,000 men showed that the those consuming the most red meat had a 30% increased risk of developing advanced PC, compared with those who consumed the least. Processed red meat also increased the risk, with a 10% increase for every 10g consumed. In a meta-analysis that included nearly 2 million participants, processed red meat consumption was associated with a dose-dependent increase in PC risk.
Don’t forget that in 2015, the World Health Organisation issued a report stating that processed red meat is a group 1 carcinogen (it’s consumption causes cancer) and red meat a group 2 carcinogen (probably causes cancer). Although the strength of association is strongest for colorectal cancer, the risk of a number of other cancers is also increased by consuming processed and red meat.
There are several mechanisms by which processed and red meat can cause cancer. The strongest evidence is for the role of nitrites and nitrates, present in processed meat, which are converted in the gut to N-nitroso compounds — known cancer-causing compounds. Haem iron in red meat is also implicated in cancer development. When meat (any meat) is cooked at high temperatures, there is formation of cancer-causing chemicals such as heterocyclic amines and polycyclic aromatic hydrocarbons.
Eggs
Some but not all studies have found an association between the consumption eggs and an increased risk of lethal prostate cancer. The main component of eggs that is implicated is choline. In a study of 47,896 men followed for 22 years, those with the highest intake of choline had a 70% increased risk of lethal prostate cancer. The exact mechanism for this potential association is not clear and there is certainly insufficient data to suggest egg consumptionhas a causal effect. However, there is a suggestion that the gut microbiomemay be implicated with metabolites formed from the consumption of animal foods resulting in an increased risk of PC.
Which foods help prevent prostate cancer?
Cruciferous vegetables
Cruciferous vegetables such as broccoli, cauliflower, Brussel sprouts and kale stand out when it comes to cancer prevention, including prostate cancer. After consumption there is generation of compounds such as sulforaphane and indole-3-carbinol that have been shown to have anti-cancer properties. Cruciferous sprouts have up to 100 times higher levels of sulforaphane and thus may be a way of maximising the health benefits of these vegetables. Cruciferous vegetables are likely to be beneficial even after a diagnosis of PC, with one study showing that men with PC who ate the most cruciferous vegetables (around one portion a day) had a 50% less chance of the cancer progressing compared to those men who ate the least.
Tomatoes and lycopene
Several studies have shown that the consumption of lycopene, the antioxidant in fruits and vegetables that gives them a red colour, is associated with a lower risk of PC. Lycopene is found in tomatoes, red peppers, watermelon, papaya, grapefruit to name a few. Tomato consumption in particular may have a protective effect, although the association is strongest for cooked rather than raw tomatoes, likely due to higher bioavailability of lycopene in cooked tomatoes. Additionally, most studies show that the protective effect occurs when there is a high level of consumption. One study reporting data from the Adventist Health Study-2, including 27934 participants and 1226 cases of PC, suggested higher intake — 5 or more times/week vs. rarely/never — of canned/cooked tomatoes (but not raw tomatoes) was associated with a 28% reduction in the risk of PC. The consumption of approximately 64g of tomatoes per day was associated with a 14% reduction in risk of PC.
Soya foods and milk
One reason suggested for the lower incidence of PC in South-East Asia is thought to be the high intake of soya products. Consumption of soya foods has been associated with a lower risk of PC in a number of studies. In fact,soya milk has been associated with a lower risk of PC, so if you are looking to swap out your dairy milk, then soya would be a good option for prostate health.
If you already have a diagnosis of PC, adding soya to the diet could also help. One study examined the impact of soya intake on PC progression. Men awaiting prostate surgery were randomly assigned to either eating a diet high in soya or not. In the soya group there was a significant decrease in the PSA level when compared to the control group.
Soya consumption is associated with a numerous health benefits, including lower cholesterol levels and better heart, kidney and bone health.
Flaxseeds
Flaxseeds are an excellent addition to any diet with a number of health benefits. The active components include alpha-linolenic acid (ALA), lignans and fibre. Although firm conclusions cannot be drawn, there is certainly interest in their role in cancer prevention, including for PC. There may also be some benefit for those with established PC. For example, a study investigating the impact of flaxseed intake on PC progression randomly assigned men awaiting surgery to having either 3 tablespoons of flaxseeds a day or not for an average of 30 days prior to surgery. At the time of surgery those that had been consuming the flaxseeds had lower levels of PC cell proliferation when compared to the control group.
Healthy drinks
Coffee consumption has been associated with a reduced risk of PC but the effect size is small with a 1% reduction in risk for each increment of one cup of coffee per day. Whereas, tea consumption in general does not appear to have a significant protective effect. The exception being that higher consumption of green tea (more than 7 cups day) may have a beneficial impact. I think overall, if you enjoy drinking tea and coffee then there is no reason to stop. However, if you do not or caffeine results in side-effects, then there are in general more impactful ways of reducing the risk of PC.
Physical activity
Meeting physical activity and exercise recommendation is key for preventing a number of chronic conditions, including cancer. The guidance for adults is for 150 minutes of moderately vigorous or 75 minutes of vigorous activity per week alongside resistance/strength exercise twice a week. Any physical activity is better than none when it comes to cancer with as little as 3–5 minutes a day reducing the risk. Therefore it seems rather counter-intuitive that the evidence for physical activity for PC prevention is not very strong. In contrast there is more robust evidence supporting physical activity interventions for those with an established diagnosis of prostate cancer, with improvements in metabolic health, fatigue, mental health and quality of life and a significant reduction in death from all causes. A randomised 12-week study of high-intensity exercise 3 times a week for 20 minutes was shown to improve cardiorespiratory fitness in men with PC and slowed progression based on PSA measurements.
Other lifestyle factors
All pillars of lifestyle medicine remain important for cancer prevention and living well after a diagnosis of cancer. Avoiding alcohol consumption and tobacco smoking and maintaining a healthy weight will support better health in general and better outcomes from PC. Although sleep disorders increase the risk of cancer and are in common in people with cancer, there are few studies specifically in PC. Maintaining health relationships and having adequate social support are also important for improving survival after a cancer diagnosis.
Diet and lifestyle factors after a diagnosis of prostate cancer
Dr Dean Ornish, American Physician and pioneer of lifestyle medicine, provided us with key evidence for the role of healthy diet and lifestyle interventions for people with a diagnosis of PC, demonstrating that it is never too late to benefit. His study of 93 men with early stages of prostate cancer randomised half to a plant-based diet, regular exercise, stress management and social support. The other group continued their usual diet and lifestyle practices. After 1 year, the intervention group had a significant reduction in the PSA level, whereas the control group had a rise in PSA level. After 2 years, 27% of the control group had to go on and have conventional treatment (surgery or radiation) compared to only 5% in the intervention group.
In separate studies the mechanism by which these lifestyle interventions might be controlling PC growth was investigated. The same lifestyle interventions in men with PC were found to increase the activity of the enzyme telomerase in blood cells, which acts to maintain the length of telomeres, and favourably alter gene expression in the prostate cells themselves. In fact, a more recent study demonstrated how a compound in cruciferous vegetables can activate genes that are implicated in suppressing the growth of PC cells.
Increased consumption of healthy plant foods has more recently been shown to improve quality of life in men living with PC. After treatment for prostate cancer, men consuming the most fruit, vegetables, whole grains, beans, nuts and seeds reported better sexual, urinary and bowel function. Plant-based diets may also improve cancer outcomes such as remission duration and survival.
Summary
Although more robust data would be beneficial when it comes to diet, lifestyle and PC, there is sufficient evidence to use lifestyle medicine interventions to reduce PC risk and improve outcomes after a diagnosis. A plant-based diet has the strongest evidence for improving cancer-related outcomes, which includes avoiding red and processed meat, dairy and alcohol. However, all pillars of lifestyle medicine remain important. Lifestyle medicine interventions can support better cardiometabolic health, mental health and well-being and quality of lifestyle for men living with a PC diagnosis.
You can find more information on a plant-based diet in our Plant-Based Eatwell Guide, adapted from the UK dietary guidelines.
