Can your diet prevent bowel cancer?

29th March 2022

Bowel cancer is one of the most common types of cancer worldwide. Eating a balanced diet is important for many aspects of health, but how much does what you eat affect your risk of bowel cancer? Can you prevent it by changing your diet? What should you avoid eating or drinking, or cut down on? And what should you eat enough of to decrease your risk?

Bowel cancer is a term for cancers that start in the colon, rectum, and anus, and can also be called colorectal cancer. It is the third most common type of cancer worldwide, with almost 2 million bowel cancer cases estimated in 2020, and the second leading cause of cancer death worldwide, second only to lung cancer.

Thanks to cancer research, we now have a good understanding of some of the key risk factors for bowel cancer. Some of these factors are out of our control, such as age and genetics. However, certain lifestyle factors that are within our control have been found to affect your risk of developing bowel cancer, such as physical exercise, maintaining a healthy weight, and eating a balanced diet.

But what food and drink should we be eating more of, or avoiding? What does the science say?​

Red meat and processed meat

Several studies have found that eating too much red meat or processed meat on a regular basis can increase your risk of developing bowel cancer. Red meat includes any meat that comes from a mammal, such as beef, pork, and lamb. Processed meat is anything that has been salted, cured, fermented, smoked, or transformed in some way to enhance the flavour or preserve it.

It is estimated that 13% of bowel cancer cases in the UK are linked to eating too much red or processed meat. To reduce your risk of developing bowel cancer, you should try to cut down on the amount of red and processed meat that you eat – no more than 500g of cooked meat each week is advised.

Fibre and bowel cancer

Eating enough fibre every day is important for overall gut health. It helps keep food moving through your bowel properly and prevents common health issues like diarrhoea and constipation, however a lack of fibre is also linked to a higher risk of developing bowel cancer.

An estimated 30% of all bowel cancer cases in the UK may be associated with low dietary fibre, so it is important to include good sources of fibre in your diet. Types of food that are high in fibre include wholegrains, nuts and seeds, beans, lentils, and fruits and vegetables.

Some studies looking at the link between fibre intake and bowel cancer could not find a clear link once other dietary factors were taken into account that may also affect the risk. However, it is still important for overall health to eat enough fibre, and a high fibre diet can help you feel full for longer. This may help to maintain a healthy body weight, which is another important risk factor for many types of cancer.

Alcohol and bowel cancer

Drinking too much alcohol is linked to an increased risk of many types of cancer, most significantly for liver cancer, but it can also increase your risk of developing bowel cancer. The human body turns alcohol into a chemical called acetaldehyde, which damages cells and prevents them from repairing that damage. This increases the chances of a cancer cell occurring.

The type of alcohol you drink and your pattern of drinking (regular versus binge drinking) do not affect your risk of bowel cancer, it is the amount of alcohol consumed that matters. Reducing the amount that you drink can lower your risk of developing bowel cancer but also many other cancers and other health problems caused by excess drinking.

Vitamin D and bowel cancer

Vitamin D is created by the body when skin is exposed to sunlight but can also be found naturally in certain foods such as oily fish. Some types of food like bread and milk can be fortified and have vitamin D added to them, and daily supplements for vitamin D are widely available. This is because it is very important for overall health to have enough vitamin D. Low levels have been associated with many health conditions and poor immune system function, and it may also affect the risk of bowel cancer.

Some studies have found that having health levels of vitamin D is protective against bowel cancer. One example found that higher levels of vitamin D in the blood decreased this risk by up to 26%, although others found this effect to be true for women but not men, and some did not find a clear link. More research may make this relationship clearer, however getting enough vitamin D is still important for many aspects of health.

Will eating bacon sandwiches give me bowel cancer?

No, although some foods like bacon tend to pop up online as ‘cancer causing foods’, there is no single item of food that will give you bowel cancer. However, there are categories of food that, if eaten regularly over a long period of time, could increase your risk. Bacon is a processed food, which research as shown can increase your risk of bowel cancer. This means that, while it’s OK to enjoy the occasional bacon sandwich, you shouldn’t enjoy them too often.

Can I cure bowel cancer by changing my diet?

No, you cannot cure bowel cancer by eating certain foods or changing what you eat. Sometimes, people diagnosed with bowel cancer may be advised to change their diet, however this is often to alleviate symptoms or because they may have had treatments that make it difficult to digest certain foods. A balanced diet, alongside regular exercise and maintaining a healthy weight, can reduce your risk of many types of cancer, however once cancer has developed other medical interventions are needed.

How do scientists study the link between diet and cancer?

How is data on diet and cancer collected?

When scientist want to gather information on the link between diet and cancer, they often rely on people self-reporting what they have been eating over a set period of time. This could mean finding a group of people and following them over time, checking in with them and asking what they’ve been eating, or it could mean retrospectively asking them to describe what types of food they have been eating over the last few years. The scientists will also collect information on anyone who has been diagnosed with any type of cancer during the period of time covered by the study.

Usually, they will also collect information on other factors associated with cancer, such as family history, bodyweight, and occupation, so that they can account for the influence of these factors when looking for links between diet and cancer.

What makes studying diet and cancer difficult?

There are many things that make it hard to study the link between diet and cancer. Studies often take a long time to run, especially those that follow a group of people over time, and so can be very time-consuming and expensive. These studies also need to include a large enough group of people that any link discovered is robust.

Scientists try to account for other factors like bodyweight and smoking by collecting this information, but diet is tied to so many other factors, and can change a lot over the course of our lives, that it can be hard to show any clear links. Importantly, these studies rely on people to give a truthful, accurate account of their diet.

As it is not possible to carefully control the diets of several thousand people over many years of their lives, scientists must do what they can to make their studies as accurate as possible while accounting for many other factors.

Further reading

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