Overview

Research has shown that certain types of food have carcinogenic potential, meaning they have the ability to cause cancer. To understand what carcinogens are, it is important to first grasp how mutations arise and contribute to cancer formation.

What is cancer?

Deoxyribonucleic acid, or DNA, is a long chain of molecules that is safely stored in the nucleus of our cells.¹ It is often referred to as an instruction manual because it contains several important genetic codes that direct our cells to produce proteins.¹ This function is vital, as proteins regulate several cellular processes, including cell division, which is necessary for repair and growth.¹

So, what happens if there is a mutation (i.e. change) in the genetic code of the DNA? It is possible for cancer to develop, but it would require a combination of mutations to occur.² This involves:

• Gain-of-function mutation: a genetic change that causes a gene-promoting cell division to become overactive
• Loss-of-function mutation: a genetic change that causes a gene-inhibiting cell division to become inactive

Together, these mutations act like a car with a jammed accelerator and failed brakes, leading to uncontrollable cell division.

Why do mutations form?

Aside from mutations inherited from our parents, most mutations occur randomly within our cells. This raises the question: why doesn’t everyone develop cancer? The reason is that our cells have DNA repair enzymes that detect and correct mutations.² Although this system is not perfect, it can significantly minimise the number of mutations occurring within our cells.² 

However, exposure to external factors known as carcinogens can increase the chance of mutations.³ This can overwhelm the repair mechanisms, as it is more likely for certain mutations to escape correction and, over time, raise the risk of cancer development.³ In this article, we will be focusing on why red meat and some processed foods are classified as carcinogens in our diet. 

Defining red meat and processed foods

Red meat

Red meat is the fresh meat of mammals, such as cattle, sheep and pigs.⁴ They are not processed and therefore include foods such as beef, veal, lamb, mutton and pork.⁴ They are typically redder in appearance in comparison to chicken, as they have more myoglobin.⁵ Interestingly, myoglobin is a protein located in muscles, which helps supply oxygen for cellular respiration, generating energy necessary for muscle contraction.⁵ 

Processed foods

Food processing refers to any method used to alter a raw food product to make it suitable for consumption and/or extend its shelf life.⁶ According to the NOVA classification, unprocessed food includes raw products such as fruits, vegetables, meat, fish, eggs, nuts, and seeds. Conversely, when food is frozen, cooked by methods such as boiling, steaming, baking, smoking and frying, or prepared by combining different ingredients, it is considered processed.^7,8 

Processed ingredients

​​Many ingredients we commonly use at home, such as oils, butter, sugar, and salt, are already processed. These ingredients are often used in the preparation of everyday meals, like roast vegetables, sandwiches, or even a simple cup of tea. 

Processed meat

Processed meat typically refers to beef or pork that has been altered through methods such as salting, curing, fermenting, or smoking.⁴ Examples include sausages, bacon, ham, salami, and canned meat.⁴ Nonetheless, other types of meat, such as poultry, can also be processed, leading to products like chicken nuggets commonly found in fast food restaurants.⁴ 

Carcinogen classification for red meat and processed meat

The International Agency for Research on Cancer (IARC) is a specialised agency of the World Health Organisation (WHO) that has developed a system, known as the IARC Monographs to assess environmental factors for their carcinogenic potential. These factors include chemicals, biological agents or physical factors that individuals encounter through their work or daily lifestyle.³ The IARC Monographs categorise evaluated factors into the following groups:

• Group 1: carcinogenic 
• Group 2A: likely to be a carcinogen 
• Group 2B: a possible carcinogen 
• Group 3: not classifiable 
• Group 4: not likely to be a carcinogen 

Since 2015, processed meat has been ranked as a Group 1 carcinogen and red meat as a Group 2A carcinogen. According to the WHO, processed meats have demonstrated a strong link to an increased likelihood of cancer and are therefore classified as having confirmed carcinogenic potential. While red meat has also been associated with an elevated cancer risk, it has not been ranked as a Group 1 carcinogen, as studies could not rule out the influence of other underlying causes. 

Biological mechanism: how do red meat and processed food cause cancer?

There are several different ways in which red meat and processed food in the diet can result in cancer development. 

Processed food

It is important to note that not all processed foods are carcinogenic, and some, like frozen fruits, can be healthy dietary choices.⁶ However, the following processed foods have different ways in which they can be carcinogenic and should be avoided. 

Smoked meat and fish

Smoking meat and fish is a method used to preserve food by removing moisture that would benefit bacterial growth, whilst also adding a flavour that many people enjoy.⁹ However, the smoking process can produce harmful chemicals, such as polycyclic aromatic hydrocarbons (PAHs), which are known to increase the risk of cancer. This is because they can interact with DNA directly by attaching to it or indirectly by inducing oxidative stress.¹⁰ Oxidative stress occurs when PAHs trigger the formation of reactive molecules, known as free radicals, which can then damage the DNA.¹⁰ If DNA repair mechanisms fail, these interactions can introduce mutations associated with the development of cancer. This explains why regular consumption of smoked meat and fish has been particularly linked to a higher risk of colorectal, stomach and even breast cancer.^9,11,12

High in salt

Processed foods are often high in salt, notably products like soy sauce and processed meats.¹³ Frequent high salt consumption can damage the lining of the stomach, making it more vulnerable to mutations. Additionally, high salt content can promote infection by Helicobacter pylori (H. pylori), which is a bacterium linked to the progression of stomach cancer.¹⁴ 

High in fat 

Processed foods are often high in fat. Frequent consumption of high-fat foods can be harmful, as it may alter the gut microbiota and trigger inflammation.¹⁵ This creates a toxic environment where immune cells release substances, such as reactive oxygen species (ROS), which can damage the DNA of surrounding cells and contribute to cancer development.¹⁵ 

Red meat

Although red meat is not classified as a Group 1 carcinogen, studies have observed a connection between its consumption and an increased risk of oesophageal, colorectal, and stomach cancers.^16,17 This may be due to the high levels of haem iron found in red meat.¹⁸ Iron is considered carcinogenic because it can interact with DNA, induce oxidative stress, and promote the formation of N-nitroso compounds, which can also damage the DNA, potentially introducing harmful mutations.¹⁶ 

Diet recommendations

The NHS recommends the following dietary guidelines for individuals looking to reduce their cancer risk or support their health during cancer treatment: 

• Avoid processed meat: classified as a group 1 carcinogen with strong evidence linking them to colorectal, stomach and breast cancer in humans 
• Limit consumption of red meat: classified as a group 2A carcinogen with association with oesophageal, colorectal, and stomach cancer 
• Eat plenty of fruits, vegetables and wholegrains: these foods are rich in antioxidants which help neutralise free radicals and reduce the chance of DNA mutations¹⁹
• Limit alcohol consumption: heavy drinking increases the risk of stomach, liver, pancreas and prostate cancer²⁰ 
• Reduce salt intake: excessive salt can damage the stomach lining, raising the likelihood of stomach cancer
• Maintain a healthy weight: excess body fat is a risk factor linked with cancer
• Be more physically active: regular exercise helps regulate body weight and supports the overall prevention of breast, colorectal, bladder, stomach, and kidney cancer²¹ 

FAQs

How often should we eat red meat and processed meat? 

The NHS recommends cutting down red meat and processed meat consumption to 70 grams or less per day. 

Which is the healthiest cuisine?

The healthiest cuisine is Mediterranean as it contains a high proportion of vegetables and fruits.²² 

What are the healthier meat options to eat every day?

The British Heart Foundation recommends chicken or turkey mince as a healthy alternative to beef or lamb mince, as they are high in protein but lower in haem iron. 

Summary

Consumption of red and processed meat should be limited, as they have been associated with an increased risk of cancer through several biological mechanisms. Smoking meat can produce harmful compounds which can bind to and damage DNA. Processed foods are often high in salt or fat, both of which can contribute to the development of mutations. Additionally, haem iron found in red meat can promote the formation of N-nitroso compounds in the gut, which are known carcinogens. To help reduce cancer risk, the NHS recommends limiting red meat intake, avoiding processed meats, increasing consumption of fruits, vegetables, and whole grains, and maintaining a healthy, balanced diet.