Colorectal cancer prevention: the importance of diet

Colorectal cancer is a type of cancer that affects a person's rectum, colon, or both. This is also known as the large intestine.

This type of cancer is more likely to appear in older individuals, but there are many other risk factors associated with its emergence, such as genetic and lifestyle factors. Of the latter, one of the most cited risk factors is diet — referring specifically to poor dietary habits that often also lead to obesity.

Prevention: What to avoid

Numerous studies have indicated that a diet too rich in red meat is associated with a heightened risk of colorectal cancer. "Red meat" is defined by the World Health Organization (WHO) as "all mammalian muscle meat, including beef, veal, pork, lamb, mutton, horse, and goat."

A review of the evidence supporting this link notes that "consumption of red meat might be related directly to the incidence of [colorectal cancer] or indirectly because a diet high in meat tends to be low in vegetables, fruit, and fiber."

A study of North Italian populations showed that individuals who eat red meat alongside eggs, cheese, and other fatty foods — as well as refined starches — on a frequent basis had an almost twice higher risk of developing rectal or colon cancer than their peers who favored a plant-based diet.

More recent research also revealed that "a daily increase of 100 [grams] of all meat or red meat is associated with a significant 12–17 percent increased risk of colorectal cancer."

In 2015, a report published by the International Agency for Research on Cancer made the news by pointing out that every 50-gram portion of processed meat, such as bacon or salami, eaten every day increases a person's risk of developing colorectal cancer by 18 percent.

This evidence led the WHO to classify processed meats as "carcinogenic to humans."

The damage caused by unwholesome diets made the headlines again in early 2018, when a study published in The BMJ reported that "ultra-processed foods" might increase the risk of developing various types of cancer.

Prevention: What to eat

So, if a high intake of red meat and processed foods contributes to the risk of colorectal cancer, what should be eaten to protect our bodies from this outcome?

According to the ACS, a diet high in fruits, vegetables, and fibers could help to minimize the risk, and many existing studies seem to support this advice.

A study from the Loma Linda University in California found that vegetarian-style diets are linked to a decreased risk of colorectal cancer. The researchers studied four types of plant-based diet. These were:

- vegan, or strictly no products of animal origin
- lacto-ovo vegetarian, which includes dairy and eggs but no meat
- pescovegetarian, which includes fish but no meat
- semivegetarian, which includes meat and fish infrequently

All four of these plant-based diets were deemed to be less likely to lead to cancer than non-vegetarian diets.

One study from last year also suggests that the more colorful your meal the better, and that individuals should focus on integrating a rainbow of fruit and vegetables into their diets.

More specifically, their experiments on the pig model — which provides the closest resemblance to the human body in terms of metabolic processes — indicated that purple potatoes might protect against colon cancer.

That may be because these root vegetables contain compounds that reduce levels of certain pro-inflammatory proteins in the body, and inflammation is known to contribute to colon cancer risk.

Recently, researchers have also isolated a number of elements typical of Mediterranean-style diets that could help to prevent the onset of colorectal cancer.

People with a low risk of developing this condition ate plenty of fruits, vegetables, nuts, and whole grains, as well as fish and poultry, rather than red meat, and they drank little alcohol and soft drinks.

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