What Is the Link Between Obesity and Colorectal Cancer?

March 7, 2023

People affected by obesity have a greater risk for developing colorectal cancer. What are the possible connections, and what can people do to reduce their risk?


Obesity is a global epidemic. The condition and its causes are well known, yet obesity rates worldwide have nearly tripled since the 1970s. And they continue to climb. In the United States, the adult obesity rate increased in 17 states between 2020 and 2021

The World Health Organization defines overweight and obesity as “abnormal or excessive fat accumulation that may impair health.” Excess weight can put people at risk for adverse conditions like diabetes, hypertension, and cardiovascular disease.

Obesity has also been linked to the development of certain cancers, including colorectal cancer. According to the National Cancer Institute, colorectal cancer is 1.3 times as likely in people with obesity.

What Is Colorectal Cancer?

Colorectal cancer is cancer that forms in the colon or rectum. It is the third most diagnosed cancer among men and women in the United States. Rates of colorectal cancer have declined over the past few decades. This is largely because more people are getting routine colorectal cancer screenings. During some of these screening tests, like colonoscopies, doctors can remove polyps before they become cancer. 

Generally, the risk of colorectal cancer increases with age. However, cases of colorectal cancer have steadily been increasing among adults younger than 50 in the United States and in other countries, including Canada, New Zealand, and Australia. 

In 2021, the U.S. Preventive Services Task Force updated its guidelines to recommend that people at average risk for colorectal cancer start screening at age 45. Previously, the recommended age to start screening was 50. 

Read More About Colorectal Cancer Screening Guidelines

At this time, little is known about the reasons for the increase in early-onset colorectal cancer. So, it is not clear if and how obesity may be associated with the increase. However, obesity is a known risk factor for colorectal cancer.

How Are Obesity & Colorectal Cancer Linked?

There are several possible reasons why obesity may increase the risk for colorectal cancer. Researchers have been exploring the potential connections. Studies include the ways obesity can impact the function of essential hormones and other processes in the body. 

Possible connections include:

Chronic inflammation: Excess fat can create a low-oxygen environment, leading to inflammation, which can increase people’s risk of cancer.1 Obesity-related inflammation has been linked to colorectal carcinogenesis (when normal cells become cancer cells).2 However, more research is needed to identify specific factors that may connect inflammation and cancer, including colorectal cancer.3

Insulin: People with obesity are at risk for developing insulin resistance.4 With insulin resistance, the body becomes resistant to processing glucose and, thus, more insulin (a hormone that regulates blood sugar) is created. High levels of insulin and insulin-like growth factor 1 may promote the growth of colon cancer and certain other cancers.5,6

Leptin: People affected by obesity have increased levels of leptin, a hormone mainly produced by fat cells.6 One of leptin's primary roles is to help people feel sated, or full, when eating. It also has been shown to contribute to growth in colonic epithelial cells and may play a role in the development of colorectal cancer tumors.2,6,7

Gut microbiome imbalance: The gut microbiome refers to the many different microorganisms that live in our gastrointestinal tract. The gut microbiome helps with important processes in the body like nutrient absorption.8 Researchers are exploring the ways an imbalance in these microbes (dysbiosis) may be linked to the development of cancer,5 including colorectal cancer.8 For example, obesity during childhood and infancy has been shown to cause a gut microbiome imbalance and inflammation, which may lead to early-onset colorectal cancer.8

How Can a Healthy Diet and Exercise Help?

Some risk factors for obesity can’t be changed, such as certain health conditions and genetics. But other risk factors, like an unhealthy diet and lack of physical activity, are lifestyle behaviors that can be changed. 

View Risk Factors for Colorectal Cancer 

By eating a healthy diet and getting regular exercise, people can lower their risk of developing obesity. These are also effective methods to treat obesity. In addition, a healthy diet and lifestyle may reduce people’s risk of developing colorectal cancer. Daily exercise and nutritious foods like whole grains, fruits, and vegetables can help support good colon health.

Watch this short video showing you how to make a colorful lentil soup in one pot. It's packed with nutrients & fiber to strengthen the immune system and promote regular bowel movements. Search our Kitchen for more healthy cooking videos to help with specific eating challenges.

The American Cancer Society offers tips to maintain a healthy diet and weight

  • For adults, get at least 150-300 minutes of moderate exercise each week (for children and teens, 1 hour of moderate to vigorous activity per day is recommended)
  • Limit sedentary activities, such as sitting and watching TV 
  • Limit or avoid highly processed foods, red and processed meats, and sugar-sweetened drinks
  • Eat fruits and vegetables in a variety of colors
  • Choose whole grains over refined grain products

For people with obesity, education and support resources are available through organizations like the Obesity Action Coalition. The OAC works to elevate and empower those affected by obesity through education, advocacy, and support. 

Eating Well & Staying Active After a Colorectal Cancer Diagnosis

Establishing a healthy diet and exercise routine can have physical and mental health benefits for people who are navigating a cancer diagnosis or life post-treatment.

Eating well and staying active during cancer treatment can help minimize adverse side effects like weight loss and lack of appetite. It can also help patients:

  • Maintain a healthy body weight and muscle mass
  • Gain more energy
  • Improve their response to treatment

Always be sure to consult with your doctor or primary care provider before making any lifestyle changes that may impact your cancer treatment. 

Maintaining a healthy diet and lifestyle after treatment ends can help cancer survivors reduce the risk of a future cancer diagnosis. It can also help survivors:

  • Recover and heal
  • Regain strength
  • Maintain a healthy weight
  • Manage any ongoing side effects

Discover a Dietitian's Tips to Eat Well With Cancer



1. Underferth, D. 2017. How Does Obesity Cause Cancer? MDAnderson.org.

2. Ye, P, Xi, Y, Huang, Z, Xu, P. 2020. Linking obesity with colorectal cancer: Epidemiology and mechanistic insights. Cancers. 

3. Stone, T, McPherson, M, Darlington, LG. 2018. Obesity and cancer: existing and new hypotheses for a causal connection. EBioMedicine. 

4. Wu, H, Ballantyne, CM. 2020. Metabolic inflammation and insulin resistance in obesity. Circulation Research. 

5. Obesity and Cancer. National Cancer Institute. Cancer.gov. 

6. Gribovskaja-Rupp, I, Kosinski, L, Ludwig, KA. 2011. Obesity and colorectal cancer. Clinics in Colon and Rectal Surgery. 

7. Chun, KA, Kocarnik, JM, Hardikar SS, et al. 2018. Leptin gene variants and colorectal cancer risk: sex-specific associations. PLoS One. 

8. Rebersek, M. 2021. Gut microbiome and its role in colorectal cancer. BMC Cancer.