Fact-Check: Do These Everyday Habits Really Raise Colon Cancer Risk?

The claims, and how we checked them

A list of five everyday habits said to raise colon cancer risk circulates widely: sitting for long stretches, eating too little fiber, drinking alcohol, smoking, and putting off screening.

We checked each claim against the National Cancer Institute, the FDA, the American Cancer Society, and the World Health Organization's cancer agency. The magazine article that spread this list now sits behind a paywall. So what follows tests the claims themselves.

The short answer: four of the five hold up. One is softer than it usually gets stated.

The scale of the problem

ACS estimates about 108,860 new colon cancers and 49,990 new rectal cancers in the United States in 2026. That is roughly 158,850 combined, with about 55,230 deaths.

Overall rates have fallen since the mid-1980s, by about 1 percent a year from 2013 to 2022. That drop is in older adults.

In people under 50, rates rose 2.9 percent per year over the same span. In adults aged 50 to 64, they rose 0.4 percent. Death rates in people under 55 have risen about 1 percent a year since the mid-2000s.

So "rising in younger adults" is right. It is why screening now starts at 45.

Claim 1: sitting too much. Supported.

NCI lists physical activity as a protective factor. A lifestyle with regular activity is linked to a lower risk of colorectal cancer.

NCI also lists obesity as a risk factor. It is linked both to getting colorectal cancer and to dying from it.

The claim is about a pattern over years, not one lazy afternoon. Our page on physical activity and cancer has the detail.

Claim 2: too little fiber. This is the soft one.

Fiber is good for you, and high-fiber foods belong in a sensible diet. But the claim that low fiber raises colon cancer risk is not what NCI says.

NCI's prevention summary puts diet in its "not clear" category. Its wording: it is not known if a diet low in fat and meat, and high in fiber, fruits, and vegetables lowers the risk of colorectal cancer. Some studies show a high-fat, high-meat diet raises risk. Others do not.

That is an unsettled question, stated plainly by the agency that reviews the evidence. Eating more fiber is sensible anyway. Saying it prevents colon cancer goes further than NCI will.

Claim 3: alcohol. Supported.

NCI states there is strong evidence that alcohol drinking can cause cancer. IARC classified alcohol as a Group 1 carcinogen in 1987.

For colorectal cancer, NCI puts the risk at 1.2 to 1.5 times as likely in moderate to heavy drinkers. Its prevention summary adds that three or more drinks a day raises the risk.

On mechanism, NCI describes the body breaking ethanol down into acetaldehyde. That is a toxic chemical and probable human carcinogen, and it can damage DNA and proteins. NCI also notes that even light drinkers face raised risk of some cancers. Our page on alcohol and cancer risk goes through the numbers.

Claim 4: smoking. Supported.

NCI states that cigarette smoking is linked to a higher risk of colorectal cancer and of death from it. Smoking is also linked to forming colorectal adenomas, the benign growths that can turn into cancer.

NCI adds one detail worth knowing. Smokers who have had adenomas removed are at higher risk of those adenomas returning.

Claim 5: delaying screening. Supported, with a caveat about blood tests.

ACS says people at average risk should start regular screening at 45. Those in good health, with a life expectancy over 10 years, continue through 75. From 76 to 85 the decision is individual. After 85, ACS says screening should stop.

ACS prefers annual FIT or gFOBT, stool DNA or RNA tests every 3 years, colonoscopy every 10 years, CT colonography every 5 years, or sigmoidoscopy every 5 years.

Blood-based tests are listed apart from those, and ACS is blunt. They are not preferred. Use one only if unwilling to have a stool test or a visual exam.

FDA's own numbers show why. It approved the Guardant Shield blood test in July 2024 for average-risk adults 45 and older. The agency noted the test finds 55 to 65 percent of stage I colorectal cancers, and misses 87 percent of precancerous lesions. A positive result still needs a colonoscopy.

So "some screening is better than none" is true. "All screening tests are the same" is not. Our page on colorectal cancer screening compares them.

A sixth claim: red and processed meat. Supported.

IARC classifies processed meat as a Group 1 carcinogen, on evidence linking it to colorectal cancer. Red meat is Group 2A, probably carcinogenic.

An analysis of ten studies estimated that each 50-gram daily portion of processed meat raises colorectal cancer risk by about 18 percent. For red meat, IARC says that if the link proved causal, the same studies suggest 17 percent per 100-gram daily portion.

IARC also puts this in proportion. It attributes about 34,000 cancer deaths a year worldwide to diets high in processed meat. Tobacco accounts for about 1 million.

When to get checked

Symptoms are not a screening question. NCI lists these as signs of colon cancer, and they warrant a doctor's visit at any age:

• Blood in the stool, either bright red or very dark
• A change in bowel habits, including diarrhea or constipation
• A feeling that the bowel does not empty completely
• Stools that are narrower or a different shape than usual
• Gas pains, bloating, fullness, or cramps
• Weight loss for no known reason
• Fatigue or vomiting

Cases are rising under 50. Being below the screening age is not a reason to wait. Our page on colorectal cancer symptoms covers what each sign can mean.

What this does not mean

These habits are not the only causes. NCI also lists age, family history, and personal history. It lists inherited syndromes such as familial adenomatous polyposis and Lynch syndrome, plus inflammatory bowel disease and race. Black individuals have a higher risk of colorectal cancer and of death from it.

Avoiding every habit on the list does not remove risk. Some people with none of them still get the disease.

And a checked claim is not a care plan. Which test, at what age, on what interval, depends on personal and family history.

Sources

• NCI PDQ, Colorectal Cancer Prevention (Patient Version) — https://www.cancer.gov/types/colorectal/patient/colorectal-prevention-pdq
• NCI PDQ, Colorectal Cancer Screening (Patient Version) — https://www.cancer.gov/types/colorectal/patient/colorectal-screening-pdq
• NCI, Alcohol and Cancer Risk Fact Sheet — https://www.cancer.gov/about-cancer/causes-prevention/risk/alcohol/alcohol-fact-sheet
• NCI PDQ, Colon Cancer Treatment (Patient Version) — https://www.cancer.gov/types/colorectal/patient/colon-treatment-pdq
• FDA Roundup, July 30, 2024 (Guardant Shield approval) — https://www.fda.gov/news-events/press-announcements/fda-roundup-july-30-2024
• American Cancer Society, Guideline for Colorectal Cancer Screening — https://www.cancer.org/cancer/types/colon-rectal-cancer/detection-diagnosis-staging/acs-recommendations.html
• American Cancer Society, Key Statistics for Colorectal Cancer — https://www.cancer.org/cancer/types/colon-rectal-cancer/about/key-statistics.html
• WHO/IARC, Carcinogenicity of the consumption of red meat and processed meat — https://www.who.int/news-room/questions-and-answers/item/cancer-carcinogenicity-of-the-consumption-of-red-meat-and-processed-meat

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

The National Cancer Information Foundation publishes Cancer Explained. This page is for learning. It is not medical advice and does not suggest a test or treatment.

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