Evidence Based Summary:
Cancer was the second biggest cause of deaths globally in 2018 and approximately 9.6 million people died due to this disease i.e. 1 in 6 death globally .
Almost, half of the global cancer deaths could be prevented by making lifestyle choices such as avoiding tobacco, dietary changes, and immunizations against cancer-causing infections.
Cancer Quick Facts
Genes control our cells and the human body is made up of trillions of such cells. Cancer is the name given to a collection of diseases caused by changes to our genes and how they control cell function .
In business as usual scenario, when cells become old or are damaged, they are replaced by new cells. However, when cancer develops, it disrupts the above process i.e. old cells don’t die when they are supposed to, and new cells develop when they are not supposed to .
Furthermore, cancer cells keep dividing abruptly beyond their usual boundaries and can spread quickly to other body parts and may form a lump referred to as a tumour [3,4]. These cells can also invade the immune system and disrupt their normal functions .
More than 100 types of cancer have been identified to date. Risk factors include tobacco use, alcohol use, unhealthy diet, physical inactivity, UV radiation (including sun exposure) and cancer-causing infections [5,6].
The below map highlights the regional prevalence of known cancer incidents.
Cancer prevalence by type
While lung, prostate, colorectal, stomach and liver cancer are the most common among men, breast, colorectal, lung, cervix and thyroid cancer are the most common among women [5,7].
The World Health Organization estimates that cancer-related deaths would increase by 72% between 2018 – 2040 .
Red meat and cancer
Several studies have pointed out a strong correlation between consuming red meat (beef, pork, lamb and goat) and colorectal cancer, the second leading type .
Multiple types of research on red meat and colorectum cancer claim that almost 70-80 % of cases can be attributed to dietary patterns [12,13].
Processed meat (ham, salami, bacon, sausages) consumption has also been linked to the risk of bowel(colorectum) and stomach cancer, which is the third leading cause of cancer-related deaths [10,11].
Furthermore, consumption of foods preserved by salting (i.e. Salted fish, pickles, vegetables) also increases the risk of stomach and nasopharyngeal cancer [10, 11].
Having said that, there is also strong evidence that dairy products consumption can decrease the risk of colorectum cancer, however, it might increase the risk of prostate cancer due to high calcium content .
In a nutshell, different studies, including one from WHO claim that by adopting a plant-based diet, cancer-related mortality for certain types can be reduced globally [5,14,15].
Causes of Cancer
Although there are multiple risk factors for cancer, we will be only focussing on the risks associated with dietary patterns, especially meat, dairy and plant-based products consumption.
Our body needs iron but not all iron is good. Iron found in food can be classified as Haem and Non-Haem iron.
Haem iron is easily absorbed by the body and is usually found in meat, poultry and fish. However, red meat has higher concentrations of haem iron than white meat and is partially responsible for its dark colour .
Researchers have found that haem could damage the cells in the body, and as a result, they might divide more often and increase the probability of this disease.
Haem is also responsible for stimulating the bacteria in our guts to produce chemicals called N-nitroso compounds, or NOCs. Many of these are known to cause cancer [16,17].
Harmful chemicals in meat
Cooking red or processed meat at high temperatures can produce certain chemicals that can increase the risk [10,19]. A chemical called Heterocyclic aromatic amines (HAAs) is formed when meat is grilled or fried at very high temperatures [19,20].
Similarly, Polycyclic aromatic hydrocarbons (PAHs) are formed when meat is smoked or cooked over direct heat, such as barbecuing[19,20].
Both these chemicals are linked to colorectal cancer development in experimental studies based on understanding the correlation between red meat and cancer risk[10,19,20].
Nitrates – Salts
Sodium nitrate and sodium nitrite are the two common preservatives added in processed meat to enhance flavour or protect it from bacteria growing on it.
However, these salts can be converted to cancer-causing N-nitroso compounds during the curing or fermentation process [16, 21].
Salting is a traditional method of preserving raw fish as well as some vegetable pickles. There is limited evidence that Cantonese-style salted fish increases the risk of nasopharyngeal cancer .
Food preserved by salting can also increase the risk of stomach cancer by either damaging the lining of the stomach or by causing inflammation . Stomach cancer is the third leading cause of cancer-related deaths and was responsible for more than 782,000 deaths in 2018 .
Obesity is known to increase the risk of 13 types of cancer, according to Cancer Research UK. Fat cells in the body are active and can send out signals to other cells to divide more often, which can lead to this disease.
More details on the link between Obesity and Cancer in the Obesity-related article
Reducing Cancer Risk
Multiple studies have proven repeatedly that consuming a plant-based diet and reducing meat consumption reduces the risk of cancer. [23,27]. Research carried out over a period of 22 years with more than 120,000 participants concluded the following  –
One 85g serving of red meat a day increases the risk of death by 10% . One serving of processed meat (one hot dog or two slices of bacon) a day increases the risk of death by 16%.
On the contrary, research suggests that eating lots of fruit and vegetables can reduce the risk of many types of cancer as they contain a wide variety of different nutrients with properties that could make it more difficult for the disease to develop [27, 28].
Phytochemicals are naturally occurring plant chemicals that can have protective qualities for human health. There are more than 1000 types of known Phytochemicals and more are being discovered .
A few of the popular ones relevant from a dietary perspective are carotenoids, folate, vitamin C, vitamin E, selenium, flavonoids and various other naturally occurring plant substances .
Some phytochemicals and plant nutrients have the power to diffuse potential carcinogens (cancer-causing substances) and destroy them before they can cause DNA damage that may lead to cancer .
Other phytochemicals seem to make it easier for the body to make repairs at the cellular level, and the remaining may help stop the deadly cells from reproducing .
Antioxidants are chemical substances found naturally in many foods. Many Phytochemicals work as Anti-oxidants.
Some types of anti-oxidants are:
• vitamin A
• vitamin C
• vitamin E
They can prevent the body from oxidative damage which is a continuous process that can happen from the food we eat, the water we drink and the air we breathe .
Anti-oxidants also keep the ‘free radicals’ or the bad cells in check which are linked to a variety of chronic diseases .
Our body needs a continuous supply of these substances that can be ensured by regularly consuming a diet consisting of whole grains, legumes, nuts, seeds, and a variety of colourful fruits and vegetables .
Multiple studies have pointed out the link between high dietary fibre intake and a lower risk of colorectal cancer [16,21,23].
There has also been a strong correlation between consuming high fibre food like whole-grain foods (e.g. brown bread, brown rice, rolled oats), vegetables, legumes and decreased risk of bowel cancer [21,24].
A study from Cancer Research UK points out that consuming foods high in fibre can reduce the risk of bowel cancer .
Fibre-rich foods such as veggies, pulses and cereals may affect the colonic microbiota and host metabolism to alter disease risk in several ways .
Fibre is also known to dilute human faeces and at the same time increase the frequency and movements of bowels thereby reducing the time the harmful chemicals stay in the body.
A Chemical known as Butyrate is produced in the bowel when in contact with the fibre. This chemical reduces the probability of tumours developing in the bowel .
Less Saturated Fat
The below infographic from the cancer atlas summarises the risk factors related to the different types.