Behind the Headlines

Thursday September 10 2009

Tomatoes probably reduce the risk of prostate cancer

Several newspapers have reported today on a cookbook of recipes to help prevent prostate cancer. Healthy Eating: The Prostate Care Cookbook was published in June in association with the Prostate Cancer Research Foundation. The authors are reported to have called it the first example of “evidence-based cooking” and cite the growing evidence that diets rich in certain foods can help prevent prostate cancer and its spread.

Any book that promotes healthy eating should be welcomed and there is strong evidence that diet influences the risk of many cancers, including prostate cancer. However, the exact causes of prostate cancer are not well known at present. It is thought that age, ethnicity and a close family history of prostate cancer can affect risk.

Of the things that individuals can change for themselves, the World Cancer Research Fund says the best evidence shows that eating foods high in lycopenes, such as tomatoes, probably reduces risk. There is limited suggestive evidence that processed meat and dairy products can increase risk.

A press release about the book says that “a controlled diet can provide the most effective form of treatment”. This claim needs to be treated with caution. There are some effective forms of treatment for prostate cancer symptoms, including drugs, radiotherapy and surgery. The relative effectiveness of these treatments when compared to diet has not been tested by the researchers.

 

Where did the story come from?

The story is based on a presentation at the British Science Festival regarding a book entitled Healthy Eating: The Prostate Care Cookbook, published in June 2009. It was produced in association with the Prostate Cancer Research Foundation and written by Margaret Rayman, Professor of Nutritional Medicine at the University of Surrey, as well as researchers Kay Gibbons and Kay Dilley. The book reportedly includes recipes from celebrity chefs Raymond Blanc and Antony Worrall Thompson.

 

What is in the book?

The 176-page book begins with a foreword by the Prostate Cancer Research Foundation. An introduction of over 50 pages describes the scientific principles on which the choice of ingredients and recipe are based.

Featured foods include vegetables, fish, legumes and nutrients such as polyphenols, lycopene (from tomatoes), selenium, vitamin E and vitamin D. The rest of the book contains more than 100 recipes.

 

What does the University of Surrey press release say about this book?

Prostate cancer kills one man every hour in the UK. Tt is the second most common cancer globally after lung cancer, with over 670,000 diagnoses made each year. The researchers say there is scientific evidence of a link between prostate cancer and diet and a “growing awareness that eating the right foods can make all the difference”.

The press release claims that for those living with the condition “a controlled diet can provide the most effective form of treatment”. It discusses the best sources of polyphenols, selenium, vitamins D and E and why dairy products and certain fats can be detrimental to a person’s health.

Examples of recipes include Apricot and Brazil nut breakfast bars, and meat, fish and vegetarian dishes such as Caribbean pepper pot, Chilled tomato bisque, and Brazil nut, tomato and onion bread. Desserts include Pomegranate upside-down cake. The recipes state the key ingredients and the amount of saturated fat contained in each portion.

 

What does Cancer Research UK say about the evidence that foods can prevent prostate cancer?

CancerHelp UK, the patient information website provided by Cancer Research UK, says there has been a lot of interest in the prevention of prostate cancer in the past 10 years. The main points are that:

  • Countries that have a low fat and high vegetable intake in the diet have lower rates of prostate cancer. However, it is not certain whether this is directly due to fat intake. Studies are ongoing.
  • Lycopenes are chemicals found in tomatoes and may help to prevent prostate cancer. They are antioxidants and so may help to stop cell damage in the same way as antioxidant vitamins. All forms of tomatoes, including ketchup, contain lycopenes although the body may absorb lycopenes better if the tomatoes are processed or cooked. Some studies of lycopenes and prostate cancer have shown a reduction in risk but others have not.
  • Countries that have a high intake of soy in their diet tend to have much lower rates of prostate cancer (and other types of cancers) compared to countries where soy intake is low. This may be because of chemicals found in soy called phyto-oestrogens. Prostate cancer is less common in men in countries such as China and Japan where people eat much less fat, less red meat and have a soy-rich diet. However, because there are many other differences between Western and Chinese or Japanese populations, these findings do not conclusively prove that cutting down on fat or eating more soy lowers the risk of prostate cancer.
  • Selenium and vitamin E are antioxidant vitamins and minerals that may help to prevent cancer as part of a healthy, balanced diet. In theory, antioxidants help prevent body cells from being damaged by oxygen particles called free radicals. The damage can lead to the cells becoming cancerous. This theory was tested by a trial called the SELECT trial. However, the trial was stopped early because preliminary results showed that neither selenium nor vitamin E, taken alone or together, helped to prevent prostate cancer.
  • Stronger evidence is needed to prove that green tea helps to prevent cancer in humans.

 

What does the NHS Knowledge Service make of this book?

Any book that promotes healthy eating should be welcomed and there is strong evidence that diet influences the risk of many cancers, including prostate cancer. Unfortunately, the exact causes of prostate cancer are not well known at present. It is thought that age, ethnicity and a close family history of prostate cancer can affect your risk.

Of the things that individuals can change themselves, the World Cancer Research Fund says that the best evidence shows that eating foods high in lycopenes, such tomatoes, probably reduces risk and there is limited suggestive evidence that processed meat and dairy products can increase risk.

However, the claim that “a controlled diet can provide the most effective form of treatment” should be treated with some caution. There are some very effective treatments for the symptoms of prostate cancer including drugs, radiotherapy and surgery, which can all help prevent the spread of this disease. The relative effectiveness of these treatments when compared to diet has not been tested by the researchers.

The strength of the evidence presented in the book will need separate evaluation. Generally, observational studies showing a link between food and prostate cancer risk in healthy people provide weaker evidence than randomised controlled trials. There does not seem to be any good reason why a trial could not be designed to see if specific vitamins or foods do reduce complication rates in people who have the disease or not.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Scientists and chefs claim their recipes can help tackle prostate cancer. The Times, September 10 2009

New recipes to counter cancer. Daily Express, September 10 2009

Recipe book aims to ward off prostate cancer. The Guardian, September 10 2009

Scientists and chefs claim their recipes can help tackle prostate cancer. The Times, September 10 2009

Nutritionists' cookbook to halt prostate cancer is revealed. Daily Mail, September 10 2009

Chefs write for cancer cookbook. Daily Mirror, September 10 2009

Broccoli and tomato ketchup could prevent prostate cancer. The Daily Telegraph, September 10 2009

The recipe to beat prostate cancer. The Independent, September 10 2009

Links to the science

Eating for prostate health: The Prostate Care Cookbook by Professor Margaret Rayman, Kay Gibbons and Kay Dilley

Further reading

Boehm K, Borrelli F, Ernst E, et alGreen tea (Camellia sinensis) for the prevention of cancer. Cochrane Database of Systematic Reviews 2009, Issue 3

Dennert G, Horneber M. Selenium for alleviating the side effects of chemotherapy, radiotherapy and surgery in cancer patients. Cochrane Database of Systematic Reviews 2006, Issue 3

Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database of Systematic Reviews 2008, Issue 2

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