What You Should Know About Fiber and Cancer Risk
Published: January 7, 2026
Written by: Maddi Langweil
Medical review by: Christina Conte, RDN, LDN
Do you feel constipated? Your diet may not contain enough fiber.
Apples are a good source of both soluble and insoluble fiber, and they contain a wide variety of antioxidants and phytonutrients such as phenols and flavonoids.
High-fiber diets are a key component in preventing and reducing constipation, and they may also help keep the intestines healthy.
Fiber-rich diets offer many health benefits, from reducing the impact of chronic diseases such as diabetes to lowering the risk of certain cancers, including colorectal cancer.
Fiber is an indigestible nutrient that passes through the body when fruits, vegetables, whole grains, and other plant-based foods are consumed.
Because fiber is not digested by the body in the same way that other nutrients such as proteins, fats, and carbohydrates are absorbed, it can help increase stool bulk and reduce intestinal transit time, which supports digestive health.
“The term ‘gut health’ refers to the health of our digestive system, which is affected by our food choices.
We can improve gut health by choosing fiber-rich foods such as beans, whole grains, fruits, and vegetables.
By doing so, we help maintain a balance between good and bad bacteria in the gut, which can support immune function and reduce inflammation, among other benefits,” says Dietitian Christina Conte, who works at the Zakim Center for Integrative Therapies and Healthy Living at the Dana-Farber Cancer Institute.
“That’s why gut health is so important.”
In addition, there is a strong connection between the gut and the brain. Strengthen the mind-gut connection by maintaining a daily fiber intake.
How does fiber work and who needs it?
When the body consumes fiber, it passes through the digestive tract and is eventually eliminated by the body.
For fiber to work properly, it requires plenty of water. It is recommended to drink approximately 2–3 liters of water per day, although it is best to consult your primary care physician to determine your specific needs.
Dietitian Conte points out that a lack of water in a high-fiber diet can actually cause constipation.
“Be sure to gradually increase the amount of water you drink as you increase the amount of fiber in your diet,” says Conte. “Generally, you should drink 8 glasses or 64 ounces of water daily unless your medical team advises otherwise.”
The two main types of fiber are soluble fiber and insoluble fiber.
Soluble fiber dissolves in water to form a thick, gel-like substance during digestion and is found in foods such as oats, beans, apples, and barley.
Insoluble fiber helps move food through the digestive system and adds bulk to stool.
Nuts, beans, and potatoes are good sources of insoluble fiber.
On average, according to the American Institute for Cancer Research, people should aim to consume a total of 30 grams of fiber per day.
For every additional 10 grams of fiber consumed daily, the risk of colorectal cancer decreases by 7%.
“Most people in the United States do not consume enough fiber,” Conte notes. “Typically, we only consume about half of what we need.”
Some individuals may need to limit fiber and/or fluid intake at certain times depending on their medical history. Be sure to consult your doctor to determine what is best for you.
What are the benefits of a high-fiber diet?
Consuming fiber offers several benefits. By doing so, you may:
- Treat constipation and diarrhea by using soluble and insoluble fiber for constipation and soluble fiber for diarrhea.
- Reduce the risk of hemorrhoids, a condition that occurs when veins in the lower rectum become swollen.
- Lower cholesterol levels and blood pressure.
- Help manage blood sugar levels.
- Promote a healthy weight: fiber can prolong digestion, helping you feel full longer.
- Reduce the risk of diseases such as heart disease and diabetes.
- Help lower the risk of cancers such as colon cancer because fiber can reduce digestive transit time and help produce substances in the gut such as butyrate, which may help protect against cancer.
Is there a connection between fiber and colon cancer?
Consuming fiber is important because it helps the body eliminate waste.
There is probable evidence that consuming whole grains and fiber-containing foods protects against colorectal cancer.
In addition, limited evidence suggests that low consumption of non-starchy vegetables and fruits increases the risk of colorectal cancer.
“Current research from the American Institute for Cancer Research shows a strong connection between consuming fiber-rich foods and a reduced risk of colorectal cancer,” says Conte.
Conte also highlights that although there is evidence that a low-fiber diet increases colorectal cancer risk, the strongest evidence shows that incorporating more whole grains and natural fiber sources has a protective effect.
How can I add more fiber to my diet?
Eating more fiber may seem difficult, especially if you are already tired of tracking macronutrients. If possible, you can try:
- Choosing foods such as whole-grain cereals that contain at least 5 grams of fiber.
- Adding more fruits, vegetables, and legumes to your meals.
- Eating smaller, more frequent meals that contain fiber.
- Adding more whole grains to your diet, such as whole wheat pasta and quinoa.
Some snacks, such as nuts and dried fruits, can help increase fiber intake, but they are high in calories.
Be sure to consume these foods as part of a balanced diet rather than as meal replacements.
Are there people who should not add more fiber to their diet?
For people with a history of Crohn’s disease, ulcerative colitis, diarrhea, or recent intestinal surgery, increasing fiber intake may not be recommended.
Be sure to consult your healthcare team to determine whether increasing fiber intake is right for you.
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