Eating a healthy, balanced diet can help you keep a healthy body weight. Keeping a healthy weight is important, because obesity is the second biggest preventable cause of cancer after smoking. Visit How being overweight causes cancer to find out more.
Diet can also directly affect cancer risk. Some foods, such as processed and red meat and salt-preserved foods, can increase the risk of developing cancer. While others, such as fruits, vegetables and foods high in fibre, can reduce the risk of cancer.
For tips on ways to include foods in your diet that help keep a healthy weight and reduce the risk of cancer visit How to enjoy a healthy diet.
Which cancers are affected?
Diet has been linked with several different types of cancer:
- Mouth cancer
- Upper throat cancer
- Larynx cancer
- Lung cancer
- Stomach cancer
- Bowel cancer
How do we know which foods lower or raise the risk of cancer?
Scientists need to do very large studies to see which specific foods may reduce the risk of cancer, and which could raise the risk. Many of these studies are underway, including the EPIC study (European Prospective Investigation into Cancer and Nutrition) which was part funded by Cancer Research UK. The EPIC study is the largest study into diet and cancer to date, and it involves over 500,000 people from 10 European countries who are being followed for many years.
This section will tell you about foods that are linked to cancer risk by strong scientific evidence. For more information on the research behind this information, visit the Facts and Evidence page.
How can fruit and vegetables reduce the risk of cancer?
Eating lots of fruits and vegetables has been linked to a lower risk of mouth, throat and lung cancer.
Fruit and vegetables are an important part of a healthy diet and are an excellent source of many vitamins and minerals, as well as fibre. Fruits and vegetables can also help you keep a healthy weight as they are relatively low in calories.
How can processed and red meat increase the risk of cancer?
Processed meat includes ham, bacon, salami and sausages. Red meat includes all fresh, minced and frozen beef, pork and lamb. Fresh white meat (such as chicken) and fish are not linked with an increased risk of cancer.
Scientists think there are a number of ways in which processed and red meat can increase the risk of cancer – they involve the chemicals found in these meats. Some chemicals are a natural part of the meat, and others are made when the meat is preserved or cooked at high temperatures.
Red meat (including processed red meat) contains a naturally occurring red pigment called haem. Haem could irritate or damage cells in the body or fuel the production of harmful chemicals by bacteria, which could lead to a higher risk of cancer. Almost all red meats contain much greater amounts of haem than white meats. This may partly explain why red meats increase cancer risk while fresh white meats don’t.
Chemicals called nitrates and nitrites are often used to preserve processed meat. In the body nitrites can be converted into cancer-causing chemicals called N-nitroso compounds (NOCs). The presence of these chemicals may explain why many studies have found that processed meat increases the risk of cancer more than red meat.
Cooking meat at high temperatures such as grilling or barbecuing can produce cancer-causing chemicals called heterocyclic amines (HCAs) and polycyclic amines (PCAs).
How can foods high in fibre reduce the risk of cancer?
Many studies show that foods high in fibre reduce the risk of bowel cancer. Foods high in fibre include fruits, vegetables, pulses and wholegrain foods, but the strongest evidence is for wholegrains. While the reasons for this aren’t fully understood, dietary fibre could help protect against bowel cancer in a number of ways.
Fibre increases the size of poos, dilutes their contents, and helps people poo more frequently. This reduces the amount of time harmful chemicals in the poo stay in contact with the bowel. Fibre may also help gut bacteria produce helpful chemicals that change the conditions in the bowel. All these things could help to reduce the risk of cancer.
How can salt-preserved foods increase the risk of cancer?
Salt-preserved foods could increase the risk of stomach cancer. Salt-preserved foods include some pickled vegetables, salted fish and cured meats.
Salt could increase stomach cancer risk by damaging the stomach lining, which causes inflammation, or by making the stomach lining more sensitive to cancer-causing chemicals. Salt could also interact with a stomach bug called Helicobacter pylori that is linked to both stomach ulcers and stomach cancer.
The strongest evidence is for salt-preserved foods and mainly those commonly eaten in East Asia. The evidence linking total added salt in the diet and stomach cancer is less clear, although we cannot rule out a link.
This article was first published in the Cancer Council UK