How Obesity Increases Your Risk of Colon Cancer

Understanding Colon Cancer

Colorectal cancer, commonly called colon cancer, is the third most common cancer in the U.S. In 2020 alone, there were approximately 150,000 new cases. 

It can occur when abnormal cells in the colon (large intestine) or rectum grow uncontrollably and form polyps, or non-cancerous tumors. If left untreated, some polyps may become cancerous and spread to other parts of the body. 

Risk Factors

Several factors can increase your risk of developing colon cancer. While it can be diagnosed at any age, it’s more common in people 50 years of age and older, and African Americans may be at higher risk.

Other risk factors for colon cancer are:

• Personal or family history of polyps or cancer
• Heavy alcohol use
• Smoking
• Inflammatory bowel disease such as Crohn's disease or irritable bowel syndrome
• Inactive lifestyle
• Poor diet
• ~High intake of saturated fats (add link to examples), red meat, and processed meat
• ~Low fiber intake

Symptoms

Symptoms of colon cancer may include: 

• Changes in bowel movements  (diarrhea or constipation)
• Changes in stool consistency (narrow stools)
• Blood in stool (dark brown or black stool)
• Bright red bleeding from rectum 
• Bloating
• Continued urge to defecate despite passing stools
• Weakness or fatigue

Weight loss and abdominal pain can occur in later stages of colon cancer.

Obesity and Colon Cancer Connection

Being overweight or having obesity has been linked to a higher risk of certain cancers including ovarian, pancreatic, and breast cancers.

Obesity is caused by excess adipose tissue (body fat) and can lead to insulin resistance, hormonal changes, and chronic inflammation. These factors have been linked to increased risk of colon cancer.

Insulin Resistance

Elevated insulin is common in people with obesity. Excess abdominal fat combined with high insulin levels can lead to insulin resistance and higher risk of colon cancer.

Increased insulin also increases the production of insulin-like growth factor 1 (IGF-1), a hormone that manages the effects of growth hormones in your body. High levels of IGF-1 can have various effects on cancer cells, and may lead to tumor growth.  

Type 2 diabetes is associated with obesity, elevated insulin levels, and insulin resistance and should also be considered a moderate risk factor for colorectal cancer.

Hormonal Changes

Fat cells produce excess estrogen in people with obesity. While increased estrogen seems to be protective in postmenopausal women, it is associated with a higher risk of colorectal cancer in men and premenopausal women with a high BMI (body mass index).

Other hormones, called adipokines, are also produced by fat cells. As body fat increases, leptin increases and adiponectin decreases. If you have obesity, these hormonal changes have been linked to the development and progression of certain cancers. 

Chronic Inflammation

Fat tissue can secrete molecules (adipocytokines) that cause inflammation and promote insulin resistance. Obesity can also lead to a sedentary (inactive) lifestyle, which may further contribute to inflammation.

Preventive Measures

While more research is needed to assess the impact of weight loss on colon cancer risk, studies have been conducted to determine the potential benefits of weight loss in individuals who have undergone bariatric surgery. One study showed a 27% decrease in colorectal cancer risk in people experiencing weight loss as a result of bariatric surgery. Thus, weight loss could play an important role in risk reduction, though there may be other factors contributing as well.

Maintaining a healthy lifestyle can also reduce your risk of colorectal cancer. In addition to regular screenings, the following lifestyle changes may help prevent colon cancer:

• Limit alcohol use
• Quit smoking
• Increase physical activity
• Adopt a balanced diet
• ~Eat more fruits, vegetables, and whole grains
• ~Increase fiber intake
• ~Reduce intake of processed foods and red meats
• ~Reduce intake of saturated fats

Screening and Early Detection

Routine screening is recommended to detect colon cancer before symptoms develop. 

The American Cancer Society recommends regular screening starting at age 45 if you do not have:

• A personal history of:
• ~Colorectal cancer or certain types of polyps
• ~Inflammatory bowel disease 
• ~Hereditary colorectal cancer syndrome such as familial adenomatous polyposis or Lynch syndrome
• ~Radiation to the abdomen or pelvic areas to treat other types of cancer

• A family history of colorectal cancer

 If you do have risk factors for colorectal cancer, including obesity, talk to your healthcare provider to determine if screening should begin sooner or occur more often. 

Several screening tests, including stool (feces) sampling and visual exams such as colonoscopies, are available. Screening frequency will depend on the option you select, and if convenience is a concern, stool testing can often be done at home. Read the risks and benefits of each screening test here. Your healthcare provider can also help you determine which test is best for you. 

Keep in mind that any abnormal screening test result should be followed up with a colonoscopy if your initial testing was performed using another option.

Conclusion

Obesity can lead to insulin resistance, hormonal changes, and chronic inflammation that contribute to cell and tumor growth. 

Because many people do not experience symptoms until colon cancer has progressed, routine screening is recommended for early detection and treatment. Your healthcare provider can review your options for colon cancer screening and help you select the best option based on your age and other risk factors. 

Lifestyle changes such as diet and exercise can reduce your risk for colon cancer, and although more research is needed, weight loss may also help. 

If you are overweight or have obesity, there are medications that can help with weight loss. Talk to your healthcare provider to learn more about these options.