Dishing up on cancer

Is your diet carcinogenic?
 
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01 .Introduction

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About one-third of cancers are estimated to be caused by diet, body weight and physical inactivity – all modifiable lifestyle choices. Keeping a healthy body weight and exercising for 30 minutes a day are pretty straightforward ways to offset cancer, but it can be hard to keep track of the latest advice regarding food, especially when apparently contradictory information floods the media from one week to the next.

In this article we take you through what’s known to increase the risk of cancer, what’s known to reduce the risk and those tricky ones in between – sometimes cause and sometimes prevent cancer.

For more information on General health, see Food and health.


What increases your risk of cancer?

Acrylamide

Frying, toasting and baking some starchy foods to the point where they go dark brown can cause the formation of acrylamides, which have been found to cause cancer in animals – though not humans as yet. The International Agency for Research on Cancer (IARC), an international agency that’s part of the World Health Organization, lists acrylamide as a class 2A carcinogen – that is, it’s probably carcinogenic to humans. The main culprits are potato chips and other fried and baked forms of potatoes, as well as toast and biscuits. When you cook these foods, keeping them light brown rather than dark or burnt can reduce acrylamide formation. It’s also found in coffee.

Sugar

It’s popularly believed that sugar feeds cancer. Therefore, proponents argue, eliminating all refined sugars and other sources of sugar and carbohydrates such as bread, pasta, fruit and sweet foods and drinks can prevent or halt the progression of cancer. All cells, including cancer cells, use sugar for energy. But if they don’t get it from food, they get it from breaking down protein and fat, so starving yourself of sugar won’t help stop cancer. Furthermore, cancer sufferers need excellent nutrition to counteract the effects of treatment, and depriving yourself of entire food groups such as carbohydrates is counterproductive.

Nonetheless, that doesn’t mean a lot of sugar is okay. Emerging research suggests that excess insulin – which occurs with fast, high peaks of glucose in the bloodstream – can drive the growth of cancer cells. Also, excess sugar can lead to weight gain, and obesity is a risk factor for cancer. So it makes sense to eat a low glycaemic diet and to avoid the sugar peaks associated with excess insulin.

Artificial sweeteners, which had been shown to cause cancer in animals at extremely high doses, are considered safe for humans.

Red and processed meats

There’s convincing evidence that red meat (beef, pork, lamb and goat) and processed meat (meats preserved by smoking, curing, salting or chemical preservatives, such as hot dogs, ham, bacon and salami) increase the risk of colorectal cancer. Experts from the World Cancer Research Fund recommend limiting red meat to less than 500 grams per week, and avoiding processed meats. They also recommend that children should not be given processed meats at all.

Salt

Salt and salted foods damage the lining of the stomach, and high-salt diets are linked with stomach cancer.

Alcohol

There is convincing evidence that alcohol, even in small amounts, increases the risk of cancer of the mouth, pharynx, larynx, oesophagus and breast, as well as colorectal cancer in men. It may also increase the risk of colorectal cancer and liver cancer in women. Alcohol in mouthwash is also linked with oral cancer. In recognising the potential cardiovascular benefits of small amounts, authorities recommend limiting alcohol to less than one drink per day for women and two for men.

But it seems not all alcohol is created equal – see The Red Wine Paradox for more.


Myth busting: acidic foods and cancer

Some people maintain that eating acidic foods or foods that otherwise make the body more acidic enhance cancer cell growth and should thus be avoided in favour of ‘alkalinising’ foods.

Fact: The body’s acid-base balance is tightly regulated by the respiratory system and kidneys, and is virtually impossible to change – even a slight change in pH can be life-threatening .

 
 

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Some foods are blamed for causing as well as preventing cancer. So should you eat them or not?

Coffee

The IARC 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

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.

Milk

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.

Grapefruit

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

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.

Antioxidant supplements

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).

More information

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.



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