Foods that fend off cancer

We can do things to reduce our risk, says Professor Martyn Caplin, consultant gastroenterologist

Recent reports have highlighted that our lifetime chance of developing cancer is almost one in two. Around one in 12 women will develop breast cancer and one in 14 men will develop cancer of the prostate. Many people believe that cancer is primarily a genetic disease and that nothing can be done to prevent it. This could not be further from the truth. There is little doubt that some people are born with an inherited vulnerability to certain cancers. But for most of these individuals, this susceptibility only translates into cancer when driven by external forces. The World Cancer Research Fund and the American Institute for Cancer Research have gone as far as to suggest that most cancer is preventable, through a combination of avoiding smoking, appropriate diet, regular physical activity and maintaining a healthy body weight. But how many people really understand this? And how far are we willing to go to reduce our cancer risk?

Diet, healthy eating and cancer

A healthy diet contributes enormously to a healthy body and we know there is a strong link between diet and cancer, although the link is complex and difficult to trace because our diets are made up of so many different foods and nutrients. Experts believe that almost one in ten cases of cancer in the UK are linked to a less healthy diet and this risk is even greater if you are obese. Eating a healthy balanced diet that is high in fibre, fruit and vegetables and low in red and processed meat and salt can reduce cancer risk. A healthy body weight will significantly reduce the risk of many cancers.

‘Superfoods’ with anti-cancer properties have hit the headlines on many occasions and, while there may be some evidence that the chemicals in these foods have positive health benefits, most of the studies have been conducted in a laboratory and there simply isn’t enough evidence from large-scale studies in humans to support health benefit claims. So what do we know about the anti-cancer properties of the foods we eat?

Scientists at the World Health Organisation (WHO) set up one of the largest studies of its kind to look at the relationship between diet, lifestyle and environmental factors and the risk of cancer and other diseases. The EPIC study, as it is called, involves more than half a million people in ten European countries who are being followed for almost 15 years. The study has already helped us learn much more about the impact of different diets on cancer risk. For example, it has found strong evidence that higher levels of vitamin D in the blood are associated with a reduced risk of colorectal cancer and better survival outcomes; that dietary fibre protects against colon cancer; that high intake of fat predisposes to breast cancer; that diets high in flavonoids (anti-oxidant chemicals derived from foods such as green tea, parsley, blueberries) can reduce the risk of primary liver cancer and bladder cancer; and many more similar conclusions related to vitamin levels, diet and cancer.

pow

Tomatoes, turmeric and green tea

Other smaller studies point to the potential anti-cancer properties of a variety of diet-derived chemicals including lycopene (from tomatoes), curcumin (from turmeric) and catechins (from green tea). Lycopene is a powerful antioxidant that has been linked to a reduced risk of prostate cancer, breast cancer and liver disease/cancer. Lycopene is found in all forms of tomato and tomato products. However, most of the studies linking high levels of lycopene to a reduced cancer risk have used large doses of purified lycopene that could not be consumed in a normal diet.

Curcumin, which is extracted from the Indian spice turmeric, is a particularly interesting dietary component. Curcumin has been used as a food preservative for 4,000 years and has widespread medicinal uses in Asia. Studies suggest that curcumin inhibits many of mechanisms responsible for the development of cancer and may reduce the risk of a range of different cancers, including those of the breast, bowel, pancreas and liver. There are clinical trials of curcumin being added to chemotherapy in the treatment of bowel cancer, as previous experimental studies had shown the benefit of the combination over chemotherapy alone.

Green tea contains high levels of catechins, which have been shown in the laboratory to prevent the activation of cancer-causing chemicals and block the growth of tumour cells. Consumption of green tea has been linked with a reduction in the risk of bowel, prostate and pancreatic cancers.

Caution

Not all vitamins are good for you. For example, selenium, which may be good for pancreatic conditions, can be bad for you in combination with vitamin E if you have advanced prostate cancer. Some supplements can enhance toxicity of chemotherapy: check with your doctor, especially if you are undergoing cancer treatment.

Can we supplement our diet to reduce our cancer risk?

People who understand the importance of good nutrition in reducing their cancer risk often seek to augment their diets by eating specific foods or taking vitamins or supplements.

There is no ‘one size fits all’ combination of supplements for general health and prevention of cancerous conditions. Different organs are more at risk from certain vitamin deficiencies and, conversely, benefit from different vitamin and supplement combinations. One might consider for example, if there was a risk for bowel cancer, that specific dietary measures should be considered to optimise vitamin D and include turmeric (curcumin) and green tea.

Many individuals may not be able to take sufficient quantity of turmeric or green tea in their diet and prefer to take a supplement — making it important to choose the appropriate supplement with the best evidence base. The scope is much broader for other non-cancerous conditions; for instance, studies have shown the benefit of curcumin and green tea in reducing the relapse rate of ulcerative colitis. Research also suggests the benefit of vitamin E, curcumin and green tea in patients with hepatitis, as well as having potential benefit in primary liver cancer.

If you are interested in reducing your cancer risk, as well as thinking about your diet, you should stop smoking, aim to maintain a healthy weight, be physically active as part of everyday life and limit your intake of alcoholic drinks. Most cancer is preventable — we just need to understand the right way to go about preventing it. For more information visit www.dietandcancer.co.uk.