Colorectal cancer's characteristic tumors are spurred on by chronic inflammation, and new research shows this might be linked to a diet of ultra-processed foods high in unhealthy oils.
WHO stats show colorectal cancer is the third most common cancer worldwide and the second leading cause of cancer deaths. People over the age of 50 make up the majority of cases, but recent studies show diagnoses in younger people are on the rise.
In colorectal cancer, the body's inflammation and resolving processes – the alarm bells that recruit the body's cells to battle, or tell them when to stand down – are thrown off balance, leading to a suppressed immune system and kicking cell formation into overdrive.
When the body is fighting a tumor that won't quit, it makes sense not to add more fuel to the fire in the form of ultra-processed foods that inflame even tumor-free guts.
"It is well known that patients with unhealthy diets have increased inflammation in their bodies. We now see this inflammation in the colon tumors themselves, and cancer is like a chronic wound that won't heal," says surgery professor Timothy Yeatman from the University of South Florida (USF).
"If your body is living off of daily ultra-processed foods, its ability to heal that wound decreases due to the inflammation and suppression of the immune system that ultimately allows the cancer to grow."
Many unprocessed food sources contain a balance of fats that our bodies can use to mount an inflammatory response, and wind it down afterwards. The omega-3 in avocados, for instance, metabolizes into bioactive lipid compounds that actively resolve inflammation.
"Bioactive lipids are very small molecules derived from the foods that we eat… If the molecules are coming from processed food products, they directly imbalance the immune system and drive chronic inflammation," says USF pharmacologist Ganesh Halade.
Highly processed foods, common in a Western diet, are stripped of the lipids and fiber that would balance out the remaining excess of omega-6 fatty acids.
An example is the linolenic acid in vegetable oils (sunflower, rapeseed, canola, corn, etc), which metabolizes into arachidonic acid (AA), an important player in the pathway to inflammation. Diets high in omega-6 fatty acids have strong links to chronic inflammation and colorectal cancer, and this new study brings us closer to understanding why.
The researchers used liquid chromatography with tandem mass spectrometry (LC-MS/MS) to assess the lipids found within the colon tumors of 81 people, and in the normal mucosa of 81 matched healthy people.
The cancerous tumors were filled with molecules that promote inflammation – especially those derived from AA – and had nowhere near enough of the mediators that resolve it and promote healing.
The lipids tasked with switching between these processes were either inadequate or ineffective in the tumors, contributing to the cancer's development.
"A human's immune system can be extremely powerful and drastically impact the tumor microenvironment, which is great if harnessed correctly for health and wellness," Yeatman says. "But not if it's suppressed by inflammatory lipids from processed foods."
Restoring that balance by encouraging patients to eat healthy, unprocessed foods rich with omega-3 fatty acids and derivatives of fish oil called 'specialized pro-resolving mediators' may give their bodies much-needed relief from the chronic inflammation fueling their tumors.
The immune potential of this tumor microenvironment could be used to treat colorectal cancer, and with further research, this may prove to be the case for other tumor types, too.
This research was published in the journal Gut.