Diet facts and evidence

Read the key facts about diet and cancer risk, and find the supporting evidence from academic research and scientific studies to see why we say what we do.

People with less healthy diets are more likely to develop cancer. Many studies have been conducted looking at the association between diet and cancer, and experts agree that the food we eat can affect our risk of cancer [1, 2].

This page tells you about aspects of our diet that are linked to cancer by the current scientific evidence. Only foods which are supported by a body of good-quality evidence are included here.

For the many other foods which have been studied, the current evidence is not good enough to say for definite whether there is a link. For foods that are often linked to cancer in the media but do not have strong evidence, go to our Food Controversies page.

References

1. World Cancer Research Fund / American Institute for Cancer Research. Second Expert Report: Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective.; 2007.

2. Schuz J, Espina C, Villain P, et al. European code against cancer 4th edition: 12 ways to reduce your cancer risk. Cancer Epidemiol. 2015;39:S1-S10. View Summary on PubMed

A healthy diet can help keep a healthy weight. Being overweight increases the risk of 13 types of cancer, so a healthy diet can indirectly reduce cancer risk through weight management and prevention of obesity.  

Increasing evidence shows that an eating pattern that includes vegetables, fruits, wholegrain foods, pulses, and limits sugary drinks, processed and red meats and other high calorie foods such as fast foods is likely to prevent weight gain [1, 2].

The Government’s EatWell Guide shows how much of what we eat overall should come from each food group to achieve a healthy, balanced diet over a day or even a week. A simple way recommended by dietitians to achieve this balance at one meal is to fill half your plate with non-starchy colourful vegetables/salad, ¼ with healthy protein foods like fish or beans and ¼ with wholegrain foods like brown rice or other starchy foods [3].

Diets that are high in fruits, vegetables, wholegrain foods and pulses and low in sugary drinks, processed and red meat and fast food could prevent weight gain through increasing the feeling of fullness, reducing overall food intake and reducing calorie intake [2].

Some of the same dietary components that could impact on weight, can also affect cancer risk independently of weight. High fibre foods like wholegrains, pulses, fruit and vegetables, that help keep a healthy weight, have also been shown to reduce the risk of some cancers. Processed and red meat, that increase the risk of weight gain, also increase the risk of bowel cancer. Read more about this evidence in the sections below.

References

1. NICE. Preventing excess weight gain. Nice Guid. 2015;(March). https://www.nice.org.uk/guidance/ng7. Accessed October 24, 2016.

2. Swinburn BA, Caterson I, Seidell JC, James WPT. Diet, nutrition and the prevention of excess weight gain and obesity. Public Health Nutr. 2004;7(1A):123-146. View Summary on PubMed

3. Brown A. Weight loss food fact sheet, British Dietetic Association. https://www.bda.uk.com/foodfacts/Want2LoseWeight.pdf. Accessed October 24, 2016.

Research has suggested that eating fruit and vegetables could reduce the risk of mouth, upper throat, larynx and lung cancers [1-4].

Fruit and vegetables contain a wide variety of different nutrients with properties that could make it more difficult for cancer to develop. These nutrients include carotenoids, folate, vitamin C, vitamin E, selenium, flavonoids and various other phytochemicals (chemicals found in plants) [5].

Fruit and vegetables are also a very good source of natural fibre [6] and there is strong evidence that eating foods high in fibre reduces the risk of bowel cancer [7].

There is strong evidence that the nutrients in fruit and vegetables do not reduce the risk of cancer when they are taken as supplements. High doses of supplements could even have harmful effects [8, 9].To find out more about vitamins and mineral supplements, go to our Food Controversies page.

In the UK, most of us do not eat the recommended amounts of fruit and vegetables [10].

References

1. Vieira AR, Abar L, Vingeliene S, et al. Fruits, vegetables and lung cancer risk: a systematic review and meta-analysis. Ann Oncol. 2016;27(1):81-96. View Summary on PubMed

2. Wang M, Qin S, Zhang T, Song X, Zhang S. The effect of fruit and vegetable intake on the development of lung cancer: a meta-analysis of 32 publications and 20 414 cases. Eur J Clin Nutr. 2015;69(11):1184-1192. View Summary on PubMed

3. Liu J, Wang J, Leng Y, Lv C. Intake of fruit and vegetables and risk of esophageal squamous cell carcinoma: a meta-analysis of observational studies. Int J Cancer. 2013;133(2):473-485. View Summary on PubMed

4. Maasland DHE, Van Den Brandt PA, Kremer B, Goldbohm RA, Schouten LJ. Consumption of vegetables and fruits and risk of subtypes of head-neck cancer in the Netherlands Cohort Study. Int J Cancer. 2015;136(5):E396-E409. View Summary on PubMed

5. World Cancer Research Fund / American Institute for Cancer Research. Second Expert Report: Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective.; 2007.

6. British Nutrition Foundation. Dietary Fibre. https://www.nutrition.org.uk/healthyliving/basics/fibre.html. Accessed October 24, 2016.

7. World Cancer Research Fund / American Institute for Cancer Research. Continuous Update Project Report: Food, Nutrition, Physical Activity, and the Prevention of Colorectal Cancer. 2011;50(2):167-178.

8. Martínez ME, Jacobs ET, Baron JA, Marshall JR, Byers T. Dietary supplements and cancer prevention: Balancing potential benefits against proven harms. J Natl Cancer Inst. 2012;104(10):732-739. View Summary on PubMed

9. Bjelakovic G, Nikolova D, Ll G, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. 2012;(3):3-5. View Summary on PubMed

10. Public Health England, Food Standards Agency. National Diet and Nutrition Survey Results from Years 5 and 6 (Combined) of the Rolling Programme 2012 / 2013 – About Public Health England. Vol 6.; 2016.

People have been advised to increase to eat more fruit and vegetables since the 1990s. Since then, many expert reports on diet and cancer prevention have supported eating at least five portions of fruit and vegetables a day [1-3]. In 2005 the Department of Health made a concerted effort to promote their 5 a day programme [4].

Eating plenty of fruit and vegetables can also help you keep a healthy body weight. There is strong evidence that obesity increases the risk of 13 types of cancer, including bowel and breast (post-menopausal). Eating plenty of fruit and vegetables can also reduce the risk of other diseases including heart disease [5].

1. World Cancer Research Fund / American Institute for Cancer Research. Second Expert Report: Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective.; 2007.

2. IARC Handbooks of Cancer Prevention. Fruit and Vegetables. Lyon. 2003;8.

3. WHO. Diet, nutrition and the prevention of chronic diseases. World Health Organ Tech Rep Ser. 2003;916: 1-149. View Summary on PubMed

4. Department of Health. Choosing a Better Diet : A Food and Health Action Plan.; 2005.

5. Gan Y, Tong X, Li L, Cao S, Yin X. Consumption of fruit and vegetable and risk of coronary heart disease: a meta-analysis of prospective cohort studies. Int J Cardiol. 2015;183:129-137. View Summary on PubMed

Eating a diet high in processed and red meat can increase the risk of bowel cancer [1-3].Red meat includes all fresh, minced and frozen beef, pork and lamb. Processed meat includes ham, bacon, salami and sausages [1].

The International Agency for Research on Cancer classifies processed meat as a cause of cancer, and red meat as a probable cause of cancer [4]. Scientists estimate around a quarter of bowel cancer cases in men, and around a sixth in women, are linked to eating red or processed meat [5]. Bowel cancer risk increases by nearly a fifth (17%) for every 100g of red meat eaten per day, and by a similar amount (18%) for every 50g of processed meat eaten per day [6].

There is also some evidence linking red meat to pancreatic cancer and prostate cancer, and processed meat to stomach cancer, however this is still uncertain [4, 7-10]. 

There is no strong evidence that eating fresh white meat, such as chicken, or fish increases the risk of cancer [11].

In the UK, the Government advises that people who eat more than 90g (cooked weight) of red and processed meat a day should cut down to 70g or less [12]. 

Processed and red meat contains chemicals that could cause cancer

There are a few different ways red and processed meat could increase the risk of cancer. The biological reasons for the link between red and processed meat and cancer are still unclear, but it is likely that chemicals found in red and processed meat play a part [6, 8, 13].

Haem

Red and processed red meat contains a red pigment called haem. Haem could irritate or damage the cells in the body. The cells divide much more than normal to compensate for this damage. This increases the chance that one of these cells could acquire changes that set it down the road to cancer [14].                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         Haem could stimulate the bacteria in our guts to produce chemicals called N-nitroso compounds, or NOCs. Many of these are known to cause cancer [4, 6, 13].  Almost all red and processed meats contain more haem than white meats. This may explain why red and processed meats increase cancer risk while fresh white meats do not.

Nitrites and nitrates

Nitrites and nitrates are used to preserve processed meat and may explain why studies find that processed meat increases the risk of cancer to a greater extent than red meat [6, 8]. Nitrite and nitrates can be converted into N-nitroso compounds during the curing process and in the body. Several N-nitroso compounds can cause cancer [4, 6, 13]. In the UK, the addition of nitrates to our food is tightly regulated by the Food Standards Agency. They aim to keep the level of nitrates and nitrites added to our food as low as possible [15].

Heterocyclic amines & polycyclic aromatic hydrocarbons

Cooking meat at high temperatures can produce chemicals which may cause cancer [16]. Heterocyclic aromatic amines (HAAs) are formed in larger amounts when meats are cooked at very high temperatures, such as by frying and grilling. Polycyclic aromatic hydrocarbons (PAHs) are formed when the meat is smoked or cooked over direct heat, such as barbecuing [4, 13].

References

1. Chan DSM, Lau R, Aune D, et al. Red and processed meat and colorectal cancer incidence: Meta-analysis of prospective studies. PLoS One. 2011;6(6). View Summary on PubMed

2. Larsson SC, Wolk A. Meat consumption and risk of colorectal cancer: A meta-analysis of prospective studies. Int J Cancer. 2006;119(11):2657-2664. View Summary on PubMed

3. Norat T, Bingham S, Ferrari P, et al. Meat, fish, and colorectal cancer risk: The European Prospective Investigation into Cancer and Nutrition. J Natl Cancer Inst. 2005;97(12):906-916. View Summary on PubMed

4. Bouvard V, Loomis D, Guyton KZ, et al. Carcinogenicity of consumption of red and processed meat. Lancet Oncol. 2015;16(16):1599-1600. View Summary on PubMed

5. Parkin D. 15. Cancers attributable to reproductive factors in the UK in 2010: Meat consumption. Br J Cancer. 2011;105(10):73-76. View Summary on PubMed

6. World Cancer Research Fund / American Institute for Cancer Research. Continuous Update Project Report: Food, Nutrition, Physical Activity, and the Prevention of Colorectal Cancer. 2011;50(2):167-178.

7. Larsson S, Wolk A. Red and processed meat consumption and risk of pancreatic cancer: A dose-response meta-analysis of prospective studies. Br J Cancer. 2012;106(3):603-607. View Summary on PubMed

8. World Cancer Research Fund / American Institute for Cancer Research. Diet, Nutrition, Physical Activity and Stomach Cancer.; 2016. http://www.wcrf.org/sites/default/files/Stomach-Cancer-2016-Report.pdf. Accessed October 24, 2016.

9. Zhu H, Yang X, Zhang C, et al. Red and Processed Meat Intake Is Associated with Higher Gastric Cancer Risk: A Meta-Analysis of Epidemiological Observational Studies. PLoS One. 2013;8(8).

10. Bylsma LC, Alexander DD. A review and meta-analysis of prospective studies of red and processed meat, meat cooking methods, heme iron, heterocyclic amines and prostate cancer. Nutr J. 2015;14:125. View Summary on PubMed

11. Carr PR, Walter V, Brenner H, Hoffmeister M. Meat subtypes and their association with colorectal cancer: Systematic review and meta-analysis. Int J Cancer. 2016;138(2):293-302. View Summary on PubMed

12. Scientific Advisory Committee on Nutrition. Iron and health. 2010:1-347. http://eprints.soton.ac.uk/339200/. Accessed October 24, 2016.

13. World Cancer Research Fund / American Institute for Cancer Research. Second Expert Report: Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective.; 2007.

14. Cross AJ, Pollock JR a, Bingham SA. Haem, not Protein or Inorganic Iron, Is Responsible for Endogenous Intestinal N -Nitrosation Arising from Red Meat. Cancer Res. 2003;(63):2358-2360.

15. Food Standards Agency. Food Additives Legislation Guidance to Compliance. 2015;(October 2015). http://www.food.gov.uk/sites/default/files/multimedia/pdfs/guidance/food-additives-legislation-guidance-to-compliance.pdf. Accessed October 24, 2016.

16. Sinha R, Peters U, Cross AJ, et al. Meat, meat cooking methods and preservation, and risk for colorectal adenoma. Cancer Res. 2005;65(17):8034-8041. doi:10.1158/0008-5472.CAN-04-3429. View Summary on PubMed

Eating foods high in fibre can reduce the risk of bowel cancer. Foods high in fibre include wholegrain foods (e.g. brown bread, brown rice, rolled oats), fruit and vegetables, and pulses (e.g. beans and lentils). Scientists estimate that more than one in ten (12%) bowel cancers are linked to a low fibre diet [1]. A review of all studies on the topic has shown eating 10g of fibre per day can reduce the risk of bowel cancer by around 10% [2]. Cereal fibre seems to have the most effect on reducing bowel cancer risk [2].

While the reasons for this aren’t fully understood, dietary fibre could help protect against bowel cancer in a number of ways.

Fibre dilutes the contents of poo, and increases their bulk and the frequency of bowel movements.  All of this reduces the contact time between the bowel and harmful chemicals in poo [3].

Bacteria in the bowel interact with fibre to produce several chemicals including butyrate. Butyrate changes the conditions in the bowel, so that tumours are less likely to develop [3].

 In the UK, our average fibre intake is below the recommended level [4].

References

1. Parkin D, Boyd L. 15. Cancers attributable to dietary factors in the UK in 2010: Low consumption of fibre. Br J Cancer. 2011;105(10):73-76. View Summary on PubMed

2. Aune D, Chan DSM, Lau R, et al. Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies. BMJ. 2011;343:d6617-d6617. View Summary on PubMed

3. World Cancer Research Fund / American Institute for Cancer Research. Continuous Update Project Report: Food, Nutrition, Physical Activity, and the Prevention of Colorectal Cancer. 2011;50(2):167-178. View Summary on PubMed

4. Public Health England, Food Standards Agency. National Diet and Nutrition Survey Results from Years 5 and 6 (Combined) of the Rolling Programme 2012 / 2013 – About Public Health England. Vol 6.; 2016.

There is some evidence that eating foods that have been preserved with salt could increase the risk of stomach cancer. But most evidence comes from foods eaten in countries other than the UK, like Japan [1-3].

Salt could affect the risk of stomach cancer by damaging the lining of the stomach and causing inflammation, or by making the stomach lining more sensitive to carcinogens such as nitrates. Salt could also interact with a stomach bug called Helicobacter pylori that cause both stomach ulcers and stomach cancer [3].

The link between total salt and cancer is less clear, however we cannot rule out a link. And too much salt can increase blood pressure [4] which increases the risk of heart disease and stroke [5].

In the UK, we typically eat much more than the recommended less than 6g of salt per day [6].

References

1. Fang X, Wei J, He X, et al. Landscape of dietary factors associated with risk of gastric cancer: A systematic review and dose-response meta-analysis of prospective cohort studies. Eur J Cancer. 2015;51(18):2820-2832. View Summary on PubMed

2. D’Elia L, Rossi G, Ippolito R, Cappuccio FP, Strazzullo P. Habitual salt intake and risk of gastric cancer: A meta-analysis of prospective studies. Clin Nutr. 2012;31(4):489-498. View Summary on PubMed

3. World Cancer Research Fund / American Institute for Cancer Research. Diet, Nutrition, Physical Activity and Stomach Cancer.; 2016. http://www.wcrf.org/sites/default/files/Stomach-Cancer-2016-Report.pdf. Accessed October 24, 2016.

4. Scientific Advisory Committee on Nutrition. Salt and health. Nutr Bull. 2003:134. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/338782/SACN_Salt_and_Health_report.pdf. Accessed October 24, 2016. 

5. Lewington S, Clarke R, Qizilbash N, Peto R, Collins R. Age-Specific Relevance Of Usual Blood Pressure To Vascular Mortality: A Meta-Analysis Of Individual Data For One Million Adults In 61 Prospective Studies. Lancet. 2002;360(9349):1903-1913. View Summary on PubMed

6. Sadler K, Nicholson S, Steer T, et al. A survey carried out on behalf of the Department of Health National Diet and Nutrition Survey -Assessment of dietary sodium in adults (aged 19 to 64 years) in England, 2011. 2011.

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