Colorectal Cancer Awareness Month: Diet’s Role in Cancer Risk & Survival
About Colorectal Cancer
March is Colorectal Cancer Awareness Month. Colorectal cancer is one of the most common cancers, and it is the third leading cause of cancer-related death for both men and women in the United States. In Minnesota, colorectal cancer is the third most commonly diagnosed cancer, and it is the second leading cause of cancer-related death. In 2023, it’s estimated that there will be more than 106,000 new colon cancer cases and more than 46,000 new rectal cancer cases in the United States.
Colorectal cancer starts in the colon or the rectum. These cancers are grouped together because they have much in common. The colon and the rectum make up the large intestine, which is part of the digestive system. Colorectal cancers often start as a growth, called a polyp, on the inner lining of the colon or rectum. Some polyps may develop into cancer, typically over many years. Other polyps will not turn into cancer. Polyps may grow and spread deeper into the other layers of the wall in the colon or rectum. They can also grow into blood vessels and lymph nodes and spread further in the body.
In Minnesota, American Indian populations have the highest rates of colorectal cancer cases and deaths. Colorectal cancer cases and deaths are also higher in rural areas compared to urban areas in Minnesota. These disparities may be due to lower screening rates, barriers to health care, and physician availability in rural areas.
Since the 1980s, colorectal cancer rates have declined overall in the United States, largely due to screening and prevention strategies. However, this is largely in people over the age of 50, who are most commonly affected by colorectal cancer. In people aged 20 to 49, colorectal cancer cases and mortality rates have increased. The reason for increases in younger populations is unknown.
Colorectal Cancer Risk Factors
Risk factors are things that increase your chances of developing cancer. Some risk factors you can change, while others you can’t. Some risk factors for colorectal cancer that you cannot change include aging, personal or family history of polyps or cancers, an inherited syndrome, having other conditions like inflammatory bowel disease and type 2 diabetes, and racial or ethnic background.
On the other hand, it is estimated that 55 percent of colorectal cancer cases could potentially be prevented by modifying risk factors and behaviors. Some of these risk factors include being overweight or obese, not being physically active, smoking, and alcohol consumption. One of the most significant risk factors for colorectal cancer is eating certain diets. Much of colorectal cancer research, especially around cancer prevention, has focused on diet and nutrition.
Colorectal Cancer Risk & Diet
One of the main dietary contributors to colorectal cancer risk is meat. Diets high in red meat, such as beef, lamb and pork, can increase the risk of developing colorectal cancer. This is also true for processed meats. These are meats that are smoked, salted, cured, or fermented, such as ham, bacon, deli meat, and sausage. Methods of cooking meat can also be a factor. For example, cooking meat at high temperatures through frying, grilling, boiling, or charring meat can create chemicals that increase risk of developing cancer. Diets low in fiber, fruits, and vegetables and high in fats have also been linked to colorectal cancer. Fiber and certain dairy products, particularly yogurt, are potentially protective against colorectal cancer. Vitamins and minerals like calcium, folate, and vitamin D may also be protective.
Prevention & Cancer Risk Research
Research helps us understand what lowers cancer risk and how we can prevent cancer. Many prevention studies are observational. This means that researchers observe exposures (like diet) and measure outcomes (like developing or not developing cancer) to see if relationships exist between the exposures and outcomes. Researchers don’t try to make one outcome occur or change the exposure, like giving a treatment. Instead, they observe processes and exposures already occurring organically without intervening.
Some prevention studies are interventional. Researchers intervene in these studies to observe a specific change, like an exposure or treatment. For example, researchers may assign one group of participants to take a vitamin, while the other group receives a placebo or a lower dose of the vitamin. Researchers then measure outcomes for both groups to see if the intervention, in this case a vitamin, is more effective than the alternative.
Learn more about prevention trials and what it’s like to participate on the MNCCTN blog.
What Colorectal Cancer Research Tells Us: Prevention
Some cancer prevention studies focus on colorectal cancer, cancer more broadly, or effects in the body known to increase risk for cancer, such as inflammation. Some colorectal cancer studies focus on specific foods or food groups, like red meat or brown rice, while others study dietary patterns and lifestyles, like a Western diet or a plant-based diet.
One observational colorectal cancer study compared a Western diet (a diet high in red and processed meats, high-fat dairy products, refined grains, and desserts) to a prudent diet (a diet high in vegetables, fruits, whole grains, and fish). Researchers wanted to examine overall dietary patterns instead of individual foods because they thought this better represented real-world situations. More than 137,000 study participants were followed for up to 32 years, and their dietary patterns, lifestyle behaviors, medication use, and diagnoses of colorectal cancer were tracked through regular questionnaires. Researchers found that people who consumed more of a Western diet had a 31 percent increased risk of developing colorectal cancer. On the other hand, people who consumed more of a prudent dietary patterns had a 14 percent decreased risk of developing colorectal cancer.
A 2021 review and analysis of 45 previous observational studies that assessed dietary patterns and colorectal cancer risk reaffirmed risk and protective factors. The review found that Western diets and higher intake of red meat and alcohol increased risk of developing colorectal cancer. It also found that higher fiber, calcium, and yogurt intake decreased risk of developing colorectal cancer.
What Colorectal Cancer Research Tells Us: Survival
Diet isn’t only linked to colorectal cancer prevention. Studies have shown that diet impacts colorectal cancer recurrence and survival as well. A 2007 observational study enrolled more than 1,000 patients with stage III colon cancer who received the same type of chemotherapy and followed them for 5 years. Participants’ dietary patterns and outcomes were measured. Western diets were categorized by higher intakes of red and processed meat, high-fat dairy, refined grains, and desserts. Prudent diets were categorized by higher intakes of fruit, vegetables, whole grains, legumes, and poultry. Researchers found that people who ate more of a Western diet were 2.9 times more likely to have a cancer recurrence compared to those who ate a prudent diet. People who consumed a more Western diet were also more likely to die from colorectal cancer.
Learn More about Colorectal Cancer and Cancer Prevention
If you have questions about colorectal cancer, diet, or prevention trials, reach out to your provider or contact the Masonic Cancer Center Nurse Navigator Line at 612-624-2620 or ccinfo@umn.edu.
Check out more colorectal cancer and cancer prevention articles and resources from MNCCTN and other cancer research organizations:
Cancer Prevention Month: Prevention Trials
Colorectal Cancer Awareness Month: Cancer Screening Advancements
Cancer Prevention Month: Role of Diet & Nutrition