However, there is little proof of the relative benefits and risks of eating different amounts of specific foods, and no single factor is known to either cause or prevent the disease. More information on diet and prostate cancer will be provided by the European Prospective Investigation into Cancer and Nutrition (EPIC), a major study that has been monitoring more than 130,000 men since 1993. In the meantime, it makes sense to follow basic healthy eating guidelines; some simple advice is listed below.
- Eat plenty of fruit and vegetables (at least 5 portions a day)
- Eat plenty of cereal foods, ideally unprocessed
- Maintain ideal body weight (body mass index 20–25 kg/m2)
- Limit fatty foods
- Eat red meat and processed meat in moderation
- Avoid high doses of vitamin supplements
- Consume alcohol in moderation
- Avoid highly salted, burnt, and mouldy foods
Prostate cancer is one of the most common cancers in Western countries yet no one knows precisely what causes it. From studying the characteristics of men with prostate cancer, researchers have pinpointed a number of factors that may increase a man’s likelihood of developing the disease, one of which is diet. While not as significant a risk factor as age (half of all cases of prostate cancers are diagnosed in men aged 75 years and older), there is evidence that certain foods may increase the risk of developing prostate cancer, while other foods may protect against the disease. There is also growing interest in using diet to treat prostate cancer, with preliminary research suggesting that specific foods may help slow the growth and spread of tumours. The links between various dietary factors and prostate cancer are discussed below.
Several lines of evidence suggest that eating a high-fat diet raises the risk of prostate cancer. Research indicates that a country’s prostate cancer mortality rate is related to the average total calories consumed by the population. In addition, many studies have identified dietary fat intake as a common distinguishing factor between men with and without prostate cancer. Fat of animal origin appears to carry the highest risk, although polyunsaturated vegetable fats have also been linked to prostate cancer.
A large US study found that individuals who ate a lot of animal fat, particularly from red meat, were at increased risk of developing advanced prostate cancer (where the cancer has spread to other areas of the body). Yet another study found that men with prostate cancer who ate a low-fat diet had tumours that grew and spread more slowly than comparable men who ate a high-fat diet. “As more and more men are diagnosed with early-stage disease, it becomes increasingly important to consider how dietary or lifestyle changes could decrease their risk of cancer recurrence,” commented Dr. Alan Kristal, who led the research.
Although the evidence is not entirely consistent, there are some plausible biological explanations for a link between dietary fat and prostate cancer. For instance, dietary fat may increase levels of hormones called androgens, which are known to promote the development of prostate cancer. Alternatively, certain types of fatty acids may initiate or encourage prostate tumour growth, although the evidence for this is conflicting. An interesting observation in animals is that the male offspring of rats who ate a high-fat diet while pregnant are more likely to develop prostate cancer than rats whose mothers ate a low-fat diet.
Some experts believe that a high calcium intake can increase the risk of prostate cancer. For instance, a study conducted in Seattle found that men who consumed more than around 1200 mg/day of calcium were twice as likely to be diagnosed with advanced prostate cancer as those who took less than 500 mg/day. In addition, the Harvard-based Physician's Health Study indicated that higher levels of calcium may increase the risk of prostate cancer, but only by 20–30%. Other researchers have concluded that moderate levels of calcium intake appear to have little or no impact on cancer risk. The issue is further complicated because vitamin D, which is often found in the same foods as calcium, helps to lower the risk of prostate cancer. Some scientists believe that high calcium intake suppresses vitamin D levels, thereby losing the protection afforded by this vitamin.
In 1998 a major study conducted in Finland found that male smokers who took vitamin E supplements were markedly less likely to develop prostate cancer or die from the disease than men who did not take the supplements. A separate trial, conducted in 1996, found that men who took supplements of a substance called selenium were protected against developing prostate cancer. Both vitamin E and selenium are antioxidants, a type of molecule that is thought to control cell damage that can lead to cancer.
To substantiate the findings from these two earlier trials, a major study called SELECT is now underway. It aims to recruit more than 32,000 healthy middle-aged men who will be randomly assigned to take supplements of selenium, vitamin E, selenium plus vitamin E, or an inactive placebo. Neither the men nor the researchers will know who is taking what supplement, and the trial will continue until around 2013. At this point the researchers will “unblind” the results and compare rates of prostate cancer among the groups to determine whether either, or both, of the supplements has a beneficial effect.
Interest in soy, a bean-derived protein, was triggered by the observation that prostate cancer is rare in Asian men, whose diets are rich in soy, but common in Americans, who eat few soy-based foods. Interestingly, studies of immigrants from Japan show that native Japanese men have the lowest risk of prostate cancer, first-generation Japanese-Americans have an intermediate risk, while subsequent generations have a risk comparable to the US population. This supports the hypothesis that an outside influence, such as diet, can modulate cancer risk.
Furthermore, there are biological reasons why soy might protect against prostate cancer, since it contains hormone-like substances, called isoflavones. Research suggests that men with early-stage prostate cancer can prevent their disease from becoming worse by taking a soy isoflavone supplement every day. In this study the beneficial effect was noticed after just 12 weeks, raising the possibility that soy might be useful for preventing or slowing the development of prostate cancer.
Like soybeans, tomatoes contain a vast array of compounds with potential health benefits. One of these so-called phytochemicals is lycopene, an antioxidant that may help prevent cell damage and thus protect against cancer. Studies show that men who consistently eat at least five servings of tomatoes or tomato products each week are less likely to develop prostate cancer than men who eat smaller amounts. In addition, higher levels of lycopene in the blood have been linked with a lower risk of prostate cancer. Although lycopene can be taken as a dietary supplement, some believe that the best protection against prostate cancer comes when lycopene is combined with other phytochemicals found in tomatoes.
There is growing evidence that high-fibre diets – particularly those high in soluble fibre such as oat bran and legumes – may protect against prostate cancer. A study by Canadian researchers found that men who ate a diet rich in soluble fibre for four months had lower levels of prostate-specific antigen – a substance that indicates prostate cancer risk – than men who ate lots of insoluble fibre. The reasons for this effect are not entirely clear, however, and it is not known whether following a high-fibre diet would help prevent prostate cancer.
There is evidence to suggest that a more healthy diet can play an important role in reducing the risk of prostate cancer. Epidemiological evidence suggests that isoflavones, vitamins, minerals and antioxidants could all be beneficial in reducing the incidence of the disease. The results of ongoing studies should provide more conclusive evidence on the effect of diet on prostate cancer.
SELECT
http://www.cancer.gov/select
EPIC
http://www.iarc.fr/EPIC/
American Cancer Society
http://www.cancer.org
American Urological Association
http://www.auanet.org/
Cancer Research UK
http://www.cancerresearchuk.org
CancerBACUP
http://www.cancerbacup.org.uk
Centers for Disease Control and Prevention
http://www.cdc.gov/
National Comprehensive Cancer Network
http://www.nccn.org/
National Cancer Institute
http://www.nci.nih.gov/
References:
Armstrong B, Doll R. Environmental factors and cancer incidence and mortality in different countries, with special reference to dietary practices. Int J Cancer 1975;: 617–631.
Boileau TW, Liao Z, Kim S, et al. Prostate carcinogenesis in N-methyl-N-nitrosourea (NMU)-testosterone-treated rats fed tomato powder, lycopene, or energy-restricted diets. J Natl Cancer Inst 2003; 95: 1578–1586.
Clark LC, Dalkin B, Krongrad A, et al. Decreased incidence of prostate cancer with selenium supplementation: results of a double-blind cancer prevention trial. Br J Urol 1998; 81: 730–734.
Cummings JH, Bingham SA. Diet and the prevention of cancer. BMJ 1998; 317: 1636–1640.
Giovannucci E, Rimm EB, Colditz GA, et al. A prospective study of dietary fat and risk of prostate cancer. J Natl Cancer Inst 1993; 85: 1571–1579.
Heinonen OP, Albanes D, Virtamo J, et al. Prostate cancer and supplementation with alpha-tocopherol and beta-carotene: incidence and mortality in a controlled trial. J Natl Cancer Inst 1998; 90: 440–406.
Henderson BE, Bernstein L, Ross RK, et al. The early in utero oestrogen and testosterone environment of blacks and whites: potential effects on male offspring. Br J Cancer 1988; 57: 216–218.
Klein EA, Thompson IM, Lippman SM, et al. SELECT: the next prostate cancer prevention trial. Selenium and Vitamin E Cancer Prevention Trial. J Urol 2001; 166: 1311–1315.
Kolonel LN, Yoshizawa CN, Hankin JH. Diet and prostatic cancer: a case-control study in Hawaii. Am J Epidemiol 1988; 127: 999–1012.
Kondo Y, Homma Y, Aso Y, et al. Promotional effect of two-generation exposure to a high-fat diet on prostate carcinogenesis in ACI/Seg rats. Cancer Res 1994; 54: 6129–6132.
Kristal AR, Cohen JH, Qu P, et al. Associations of energy, fat, calcium, and vitamin D with prostate cancer risk. Cancer Epidemiol Biomarkers Pre. 2002; 11: 719–725.
Kumar NB, Cantor A, Allen K, et al. The specific role of isoflavones in reducing prostate cancer risk. Prostate 2004;59: 141–147.
Leppala JM, Virtamo J, Fogelholm R, et al. Controlled trial of alpha-tocopherol and beta-carotene supplements on stroke incidence and mortality in male smokers. Arterioscler Thromb Vasc Biol 2000; 20: 230–235.
Rose DP, Connolly JM. Dietary fat, fatty acids and prostate cancer. Lipids 1992; 27: 798–803.
Satia-Abouta J, Patterson RE, Schiller RN, et al. Energy from fat is associated with obesity in U.S. men: results from the Prostate Cancer Prevention Trial. Prev Med 2002; 34: 493-501.
Shimizu H, Ross RK, Bernstein L, et al. Cancers of the prostate and breast among Japanese and white immigrants in Los Angeles County. Br J Cancer 1991; 63: 963–966.
Tariq N, Jenkins DJ, Vidgen E, et al. Effect of soluble and insoluble fiber diets on serum prostate specific antigen in men. J Urol 2000;163: 114–118.