The evidence is overwhelming: according to the experts, we can reduce our risk of certain types of cancer by changing our diets. Medical journalist Patsy Westcott reports on the latest advice on the foods that could help save our lives.
Food vs cancer
While new drugs offer hope in the fight against cancer, many new medicines take years to become available on the market. But one anti-cancer strategy costs next to nothing and is as close as your nearest shops – yes, it’s the food you eat.
"About a third of all cancers are linked to diet, particularly colorectal (bowel), breast and prostate cancers, which are among the top four cancers (the fourth is lung)," says Professor Karol Sikora, former head of the World Health Organisation’s Cancer Programme and Medical Director of Cancer Partners UK, an organisation set up to bring high-quality cancer care closer to patients. Almost 300,000 of us in the UK will be diagnosed with cancer in the next year. But could this figure be reduced if we paid more attention to what we put in our supermarket trolley?
Sadly, it isn’t that simple. Professor Sikora points out that the food-cancer connection is not a simple equation like smoking and lung cancer.
"The dietary picture is much more complex – it’s about what we eat, what we don’t eat, how we cook it and the rest of our lifestyle – things like how much we weigh, whether we exercise and whether we drink alcohol," he says. And sadly, if you are unlucky enough to develop cancer, changing your diet "probably has very little effect, although it may make you feel better."
So what are the magic ingredients in food that can help protect against cancer? "We don’t know exactly which compounds have an anti-cancer effect," admits Professor Sikora. "But the main message is that fruit and vegetables are rich sources of antioxidant compounds that protect against cancer." The best bet is to eat plenty of fibre, reduce our intake of animal fat and eat more fruit and vegetables. Which food should we be eating more of – and which should we avoid?
Cabbage, cauliflower and broccoli, brussels sprouts, pak choi and kale
Brassicas have been found to protect against bladder, breast, colon, lung and skin cancers. They are rich in plant chemicals which are thought to have a protective effect. Scientists at Norwich’s Institute of Food Research recently found that one of these allyl isothiocyanates (AITCs), released when certain brassicas are chopped, chewed, cooked, processed and digested, put a brake on uncontrolled cell division in colon cancer cells. AITC is, in turn, a breakdown product of sinigrin, a phytochemical found in mustard, cabbage, horseradish, cauliflower, sprouts, swede, kale and wasabi.
Tuck into fibre-rich foods such as fresh fruit and vegetables, wholegrain bread, pasta and brown rice and pulses such as chickpeas, lentils and kidney beans.
A high fibre intake seems to help protect against bowel cancer and even counteract the potentially harmful effects of a meaty diet (see below). It’s thought that this is because fibre speeds the passage of foods through the gut so that potentially harmful cancer-causing compounds formed when you eat red meat spend less time in contact with cells lining the bowel walls.
Eating a portion of fish (80g) at least every other day may help protect you against bowel cancer, especially if you eat a lot of meat. Test tube and animal studies suggest that Omega 3 fatty acids found in oily fish could also help inhibit breast cancer.
Tomatoes and tomato products such as ketchup, tinned tomatoes and tomato paste contain the antioxidant lycopene.
May protect against prostate cancer, although studies have had mixed results. At the very least, though, eating plenty of tomatoes will contribute to your overall fruit and vegetable intake.
Soya products, such as tofu, soy milk or miso may lower the risk of breast, prostate and bowel cancer.
As yet, though, the action of soya on cells is not conclusive.
Green tea may reduce the risk of several cancers, thanks to the presence of high levels of plant chemicals called ‘catechins’. As yet, though, large-scale studies are needed to confirm this.
Keep your red meat intake down. Consuming more than two 80g portions of red meat such as beef, pork, lamb or veal and/or processed forms such as ham, salami and bacon a day – equivalent to a bacon sandwich and a fillet steak can up the risk of bowel cancer.
Certain proteins in red and processed meat trigger a process called nitrosation in the gut, which can lead to the formation of cancer-causing compounds. Pre-menopausal women who eat more than one and a half daily servings of red meat such as lamb, beef or pork have almost double the risk of hormone-fuelled breast cancer, compared with women who eat three or fewer servings per week.
Keep an eye on your intake of saturated (animal) fats, which are found in full-fat milk, meat and products such as biscuits and cakes. Research has shown that having more than 90g of saturated fat a day can double the risk of breast cancer, so if you’re a woman you should aim to keep your intake below 40g a day.
What you drink can have a significant effect on your risk of developing cancer. In one study reported in 2003, Cancer Research UK estimated that alcohol accounted for around four per cent of breast cancers in the developed world and around 2,000 cases each year in the UK. They calculated that the risk of breast cancer rose by six per cent for each extra alcoholic drink consumed a day. It is thought that alcohol pushes up levels of the sex hormone oestrogen in the blood, higher levels of which are linked to a greater risk of breast cancer.
According to the EPIC study, which is examining the dietary habits of more than 500,000 people across Europe over 10 years, obesity is a major risk factor for several cancers, including post-menopausal breast cancer and kidney cancer, although doctors still don’t know why. Making sure you’re the correct weight for your height by taking regular exercise and cutting down on fatty, sugary foods could help lower your risk of a number of cancers. Researchers are now trying to discover exactly why obesity may increase cancer risk in order to understand how better to prevent or treat cancer.