CRC — which occurs when tumors form in the lining of the large intestine — is the third most common type of cancer in the world, and the second leading cause of cancer-related death.^[1] Like other digestive cancers, the risk of developing CRC is higher in people who smoke, drink alcohol, are sedentary, or have obesity. Other risk factors include old age, a family history of CRC, a personal history of CRC or high-risk adenomas (polyps made of abnormal cells), or having inflammatory bowel disease. The prognosis for CRC depends on the patient’s general health, whether the cancer has spread to other parts of the body or blocked the colon, and whether cancerous cells remain after treatment.^[2]

Common signs and symptoms of CRC include a change in bowel habits (such as bloody stool, unusually narrow stool, diarrhea, or constipation), bloating, gas pains, fatigue, vomiting, and unexplained weight loss. However, CRC may not cause symptoms, which is why colorectal cancer screening is recommended for everyone over the age of 45.^[2]

A variety of tests are used to examine the intestinal lining and stool samples. During a colonoscopy or sigmoidoscopy, a thin tube with a camera is inserted into the rectum to allow the doctor to see the intestinal lining and collect biopsies for testing. Fecal occult blood tests are used to detect blood in the stool (which may not be visible to the naked eye). DNA stool tests detect changes in the genetic material of intestinal cells, which can also be a sign of CRC. If a patient is diagnosed with CRC, other tests like x-rays and CAT scans are performed to determine whether the cancer may have spread to other areas.^[2]

Surgery is the most common form of treatment, and can often cure CRC if the cancer is caught early enough. Cancerous cells and tissue can also be destroyed with heat via radiofrequency ablation, extreme cold via cryosurgery, or x-rays via radiation therapy. Chemotherapy drugs can be taken orally or intravenously, and can be more systemic (affecting the entire body) or regional (affecting one area) depending on the location of the cancer. Finally, immunotherapy can change the activity of the patient’s immune system, causing it to attack and destroy cancer cells.^[2]

A small body of evidence suggests that berberine supplementation may reduce the recurrence rate of colorectal adenomas, which commonly evolve into CRC over time.^[1] When added to chemotherapy treatment, some studies showed that some herbs used in Traditional Chinese medicine could improve quality of life, reduce some chemotherapy side effects, and enhance the tumor response to certain treatments (but the quality of evidence was low and results were inconsistent.)^[3][4][5] Probiotics and synbiotics could reduce infections and complications after CRC surgery.^[6] Vitamin D supplementation has also been studied, but conflicting study results prevent any conclusions about its ability to protect against CRC.^[7][8]

A person’s diet has a significant impact on their risk of CRC. Prudent dietary patterns — such as the Dietary Approaches To Stop Hypertension Diet (DASH) diet — have been associated with a roughly 20% reduction in the risk of CRC.^[9][10] These diets are high in fiber-rich whole grains, fruits, vegetables, and legumes, but low in red or processed meat and refined sugar.^[11][12]

Vegetarian and pescatarian diets are also associated with a lower risk of CRC compared to diets that include red meat.^[13] Garlic, cheese, and yogurt may also reduce the risk of developing CRC.^[14][15]

With the exception of wine, drinking more than one alcoholic beverage per day is associated with increased CRC risk.^[16][17]

Mediterranean-style diets and diets high in dairy or nuts are associated with lower mortality and a better prognosis in people with CRC.^[18][19][20] Diets high in processed meat, sugar, and soft drinks are associated with a worse prognosis.^[18]

Though exercise isn’t considered a treatment for CRC, engaging in at least three hours of moderate physical activity per week can increase survival rates in patients with non-metastatic CRC (cancer that hasn’t spread to other areas).^[21] Cognitive interventions — such as cognitive behavioral therapy or relaxation techniques — can improve cancer-related fatigue and both short- and long-term quality of life, while social support groups can improve short-term quality of life.^[22] Immunonutrition combines enteral or parenteral nutrition formulas with additional arginine, glutamine, and omega-3 fatty acids, and could improve post-operative recovery compared to the plain formulas.^[23]

The exact cause of CRC is unknown, but it likely results from an interaction between lifestyle and genetic factors that causes unregulated intestinal cell division. When the process of cell division isn’t controlled properly, the cells can form a tumor. Some evidence suggests that oxidative stress damages cellular DNA, proteins, and lipids, causing mutations that lead to unregulated growth.^[24] Finally, Lynch syndrome is an inheritable genetic mutation that significantly increases the risk of developing CRC.