Some foods are blamed for causing as well as preventing cancer. So should you eat them or not?
has classified coffee as a 2B carcinogen for bladder cancer, meaning it possibly causes bladder cancer. However, ongoing epidemiological research has found only a weak link, and it may be due to other lifestyle habits such as smoking (which may be more prevalent among coffee-drinkers than non-drinkers). A recent meta-analysis of epidemiological evidence found coffee, which contains antioxidants, appears to be protective against colorectal and other cancers, with growing evidence it protects against skin cancer.
Soy contains phytoestrogens – plant chemicals that have a weak hormonal effect on the body. It’s been suggested that it may increase the risk of hormonally related cancers such as breast cancer and prostate cancer. In fact, research suggests it may decrease the risk of prostate cancer, due to its inhibiting effect on the testosterone-induced growth of the prostate. Its role with breast cancer is less clear, and while it appears to be protective, women with oestrogen-dependent breast cancers are recommended to limit soy foods and avoid soy isoflavone supplements.
There is good evidence that milk protects against colorectal cancer. Conversely, diets high in calcium – which is found in milk and cheese, as well as non-dairy sources – have been linked with prostate cancer, as has milk specifically. However, the amount of calcium linked with increased risk of prostate cancer is high – 2000mg or more per day , the equivalent of consuming about 1.5L of milk every day – and up to twice the recommended daily intake. And some studies have found no link between prostate cancer and calcium, with one recent large US study finding high calcium intake reduced prostate cancer in black men but not white men.
While largely promoted for its cancer-protective antioxidants, a large, well-publicised study in 2007 found grapefruit consumption was linked with an increased risk of breast cancer. Grapefruit contains chemicals that interfere with the metabolism of oestrogen, and it’s thought that increased levels of oestrogen may have been responsible. However, subsequent larger studies have found no link between grapefruit and breast cancer, and other studies have shown grapefruit or grapefruit juice may protect against prostate cancer, pancreatic cancer and oral cancer.
Chilli contains high levels of capsaicin, which has been shown to slow the growth of tumours. However, among populations where chilli consumption is high, rates of stomach cancer are also higher . This could be because chilli may be used to disguise spoilt food, and data may be confounded by Helicobacter pylori infection (which causes stomach ulcers and cancer), lack of refrigeration or socioeconomic status.
Foods rich in antioxidants can help reduce the risk of cancer. However, high-dose supplements of some antioxidants may cause cancer: beta-carotene and retinol supplements have been found to cause lung cancer in smokers. Also, paradoxically, free radicals may be necessary to kill off tumour cells, so high doses of antioxidants may be counterproductive.
The red wine paradox
Researchers and their PR teams regularly pump out good-news stories about the cardiovascular and cancer-fighting benefits of red wine. Rich in antioxidants including resveratrol and catechins from the skin and seeds of grapes, the alcohol helps release them into the wine .
Equally, stories of alcohol – including red wine - causing cancer have been regularly thrown into the mix. Confused? Well, why wouldn’t you be?
Plugging 'red wine' and 'cancer' into the Google News search engine returned many headlines about red wine and cancer from the past 20 years, and we learned red wine fights all cancer, fights lung cancer, causes breast cancer, fights bowel cancer, causes all cancer, fights all cancer (again), fights prostate cancer, causes mouth cancer, fights breast cancer, causes breast cancer (again)…
While this might be good for continuation of research grants, it’s enough to turn us poor punters to drink!
Reduce your risk
Plant foods including fruit, non-starchy vegetables, herbs, spices, olive oil, wholegrains, nuts, seeds and legumes contain various phytochemicals known to prevent cancer, and a diet that includes a wide variety of plant foods is associated with a reduced risk of cancer.
The WHO and cancer
The International Agency for Research on Cancer (IARC) is an intergovernmental agency that’s part of the World Health Organisation (WHO). Its role is to conduct and coordinate research into carcinogens and cancer. The agency regularly reviews evidence from animal and human studies to categorise the carcinogenic potential of products and processes to humans into one of five categories:
Group 1: carcinogenic to humans (includes Helicobact pylori infection, plutonium, solar radiation, tobacco smoking)
Group 2A: probably carcinogenic to humans (includes anabolic steroids, emissions from indoor fires, diesel engine exhaust)
Group 2B: possibly carcinogenic to humans (includes DDT, lead, naphthalene)
Group 3: not classifiable as to carcinogenicity in humans.
Group 4: probably not carcinogenic to humans.
In addition to the food and drink products already mentioned on these pages, the IARC lists the following food-related products and processes as potential carcinogens: Cantonese-style salted fish (Class 1), Emissions from high temperature (>230C) frying (2A); and Asian-style pickled vegetables (Class 2B).
Food, Nutrition, Physical Activity, and the Prevention of Cancer: A global perspective is a comprehensive review of the clinical research and epidemiological studies on lifestyle factors related to cancer compiled by the World Cancer Research Fund and the American Institute for Cancer Research.
Cancer Council Australia is a national non-government cancer control organisation with the aim of facilitating prevention, research, support, and care.