Stomach cancer

Summary

Stomach cancer is the fifth most common cancer worldwide. Processed meat is associated with an increased risk; just 30g a day (half an average serving) increases the risk by 15-27 per cent. People eating the most bacon have a 37 per cent higher risk than those eating the least.

In 2015, the WHO reported links between processed meat and stomach cancer. Then in 2016, the WCRF published a report saying that that there is now strong evidence that processed meat increases the risk of stomach cancer. They also said that some evidence suggests consuming grilled or barbecued meat and fish increases the risk of stomach cancer too. They blame high levels of salt, nitrite and nitrate (that can lead to the production of harmful NOCs) as well as carcinogenic and mutagenic PAHs, haem iron and salt.

So many factors may be at play, contributing to an increased risk of stomach cancer but avoiding meat (especially processed meat) is a simple choice you can make to protect yourself. 

Stomach cancer – also known as gastric cancer – is the fifth most common cancer worldwide. Around 7,000 people are diagnosed with it each year in the UK (NHS Choices, 2015c). Unfortunately, as stomach cancer isn’t often picked up until the later stages, the outlook isn’t as good as for some other cancers. In the UK, around 5,000 people die from stomach cancer each year.

We have known about the links between processed meat and stomach cancer for over a decade. Even small amounts increase the risk and the more you eat, the bigger the risk. A 2006 review of 15 studies (including 4,704 stomach cancer patients) found that consuming just 30g per day (half an average serving) of processed meat increased the risk of stomach cancer by 15-27 per cent (Larsson et al., 2006). Seven of the studies specifically looked at the effect of bacon and found those eating the most had a 37 per cent higher risk of stomach cancer compared to those eating the least. They concluded that increased consumption of processed meat is associated with an increased risk of stomach cancer.

In 2015, the WHO announced that red and processed meat increases the risk of bowel cancer. They also reported links between red meat, pancreatic cancer and prostate cancer and processed meat and stomach cancer (WHO/IARC, 2015a). Then in 2016, the WCRF published a report from their Continuous Update Project – the world’s largest source of scientific research on cancer prevention and survivorship through diet, weight and physical activity (WCRF/AICR, 2016). They analysed worldwide research on how certain lifestyle factors affect the risk of developing stomach cancer. The report included new studies as well as those included in their 2007 report (WCRF/AICR, 2007).

For the first time, drinking alcohol, eating processed meat and being overweight were linked to an increased risk of developing stomach cancer. They said that there is strong evidence that consuming processed meat increases the risk of stomach cancer. Processed meat was defined as meat having undergone salt-preservation, smoking or fermentation, including sausages, bacon, ham, meatballs, burgers, cold meats and hot dogs. The report also said that some evidence suggests consuming grilled or barbecued meat and fish increases the risk of stomach cancer too.

How meat might cause stomach cancer

Potential mechanisms discussed in the WCRF/IARC report included the high levels of salt, nitrite and nitrate that many processed meats contain. Nitrite and nitrate from processed meat may be involved in carcinogenesis, due to reactions they trigger in the body. In the stomach in particular, nitrite and nitrate from meat can react with the degradation products of amino acids from meat to later form NOCs in the gut which are known carcinogens. Smoked meat is also often salted or cured, meaning that it is likely to raise endogenous production of NOCs. Smoked meat may also contain carcinogenic and mutagenic PAHs, depending on the fuel burned to produce the smoke.

A further potential mechanism linking processed meat intake to stomach cancer described in the report was haem iron which, as already stated, contributes to endogenous formation of NOCs, causes oxidative stress and DNA damage. Dietary iron has been identified as a growth factor for the bacteria Helicobacter pylori, an established risk factor for ulcers, inflammation and stomach cancer (Ward et al., 2012). Finally, the salt included in cooking, processing and preserving meat can damage the gastric mucosa (the stomach lining) and lead to inflammation (WCRF/IARC, 2016).

 A study from Nebraska investigating the role of haem from meat in stomach cancer found the link with endogenous NOCs was present only among people infected with H. pylori and those with relatively low blood levels of vitamin C (Ward et al., 2012). The WCRF/IARC report found evidence that consuming little or no fruit increases the risk of stomach cancer and that consuming citrus fruit may decrease the risk of stomach cancer (WCRF/IARC, 2016). So it seems that many factors may work in combination contributing to an increased or decreased risk of stomach cancer but avoiding meat (especially processed meat) is a simple choice you can make to protect yourself.

 

To find out about the foods that fight cancer (fruit, vegetables, wholegrain foods, pulses, healthy fats in nuts and seeds) please see The Incredible Vegan Health Report at www.vivahealth.org.uk