Diet, lifestyle and prostate cancer
By Dr Shireen Kassam, Director of Plant-Based Health Professionals UK
Prostate cancer affects men all around the world, with rising rates related to ageing, population growth and active screening. Black men have a significantly increased risk of prostate cancer, in part due to inherited genetic factors, and are more likely to be diagnosed at an advanced stage compared to other ethnic groups. Certain inherited genes can also be a driver of PC in White and other ethnicities. Other emerging risk factors include dairy products, deficiencies in vitamin E and selenium and occupational exposure to pesticides.
PC is not typically considered a cancer related to lifestyle behaviours, nonetheless, diet and lifestyle habits can still help to reduce the risk of developing PC and living well after a diagnosis of PC.
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-style dietary pattern, high in meat, refined grains and ultra-processed 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.
When considering the plant-based dietary index, men who adhere to a healthy plant-based diet with 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%) in risk for aggressive PC.
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 PC risk. However, when specifically assessing the impact of plant-based diets, including vegetarian and vegan, there appears to be a significant benefit for PC risk, with a vegan diet being 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. In addition, vegan and vegetarian diets improve the health of the gut microbiome. Given that obesity is a known risk factor for developing prostate cancer, a mostly or fully plant-based diet can also support a healthier body weight.
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. IGF-1 levels 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. Of note, previous studies had suggested that it was the calcium in dairy that increased the risk of PC. However, more recent analysis suggests it is dairy per se and not calcium given the lack of risk with supplemental or non-dairy sources of calcium.
Meat
Red and processed meat consumption has been associated with an increased risk of PC in some but not all studies. A large meta-analysis of studies including almost two million participants and 35,326 cases of PC found a small but significant increase in risk with the consumption of both red and processed meat. For processed meat there was a dose effect with every 50g per day consumed resulting in a 4% increase risk of PC.
Don’t forget that in 2015, the World Health Organisation issued a report stating that processed meat is a group 1 carcinogen (its 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.
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. Four to five portions of cruciferous vegetables a week seems to be the required intake for this beneficial impact.
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.
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
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 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 PCs. 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 a 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 and balance exercises 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 common in people with cancer, there are few studies specifically in PC. Maintaining healthy 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
Lifestyle interventions are important after a diagnosis of PC. Dr Dean Ornish, American physician and pioneer of lifestyle medicine, provided key evidence demonstrating that it is never too late to benefit. His study of 93 men with early stages of PC 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, Dr Ornish investigated the mechanisms by which these lifestyle interventions might be controlling PC growth. His lifestyle protocol was 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.
Further evidence supporting the role of nutrients found in plant-based foods and the potential impact of the gut microbiome comes from a randomised study in men with early stage PC. A whole food supplement of phytochemicals and lactobacillus was shown to delay progression of the disease and improve PC-specific symptoms.
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. Similarly, men consuming more plant foods and less animal-sourced foods may have improved cancer outcomes, including a reduced risk of cancer progression and improved remission duration and survival.
The STAMINA study is unique in being able to demonstrate how a diet and exercise program can be implemented into routine clinical care across the UK in people with PC. The study included men on anti-androgen therapy and was able to demonstrate that a healthy diet, inline with the UK’s dietary guidelines, and regular exercise improved quality of life, including fatigue.
Summary
There is sufficient evidence to use lifestyle medicine interventions to reduce PC risk and improve outcomes after diagnosis. A plant-based diet and exercise has the strongest evidence for improving cancer-related outcomes. However, all pillars of lifestyle medicine remain important. Lifestyle medicine interventions can support better cardiometabolic health, mental health and well-being and quality of life for men living with a PC diagnosis.
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