What happens to your poop if you don't eat enough fibre?

October 31, 2025 •

2 min read

Over 90% of US adults do not get enough fiber daily, which can have significant consequences for digestive health. If you don't eat enough fibre, the physical properties of your stool will change, often resulting in harder, smaller, and more difficult-to-pass bowel movements. This deficiency can cause immediate and long-term problems for your gut and overall well-being.

Quick Summary

A diet lacking in fiber often leads to smaller, harder, and infrequent stools, a condition known as constipation. This is because fiber adds bulk and holds water, which is essential for smooth passage through the intestines. A low-fiber diet also starves beneficial gut bacteria, leading to dysbiosis and potential inflammation. Over time, this can raise the risk of developing more serious gastrointestinal conditions.

Key Points

Constipation and Straining: Insufficient fiber leads to hard, dry stools that are difficult and painful to pass, often causing constipation.
Smaller, Less Bulky Stools: Fiber adds bulk and absorbs water, so a low-fiber diet results in smaller, more compact, and less satisfying bowel movements.
An Unhealthy Gut Microbiome: Without fiber to feed on, beneficial gut bacteria die off, causing an imbalance (dysbiosis) that can lead to inflammation.
Weakened Intestinal Barrier: The starving gut microbiome may resort to feeding on the intestinal mucus layer, weakening this protective barrier and increasing disease susceptibility.
Increased Risk of Chronic Diseases: Long-term fiber deficiency is linked to a higher risk of serious conditions, including colorectal cancer, heart disease, and type 2 diabetes.
Gas, Bloating, and Discomfort: A sluggish digestive system from low fiber often results in uncomfortable bloating and gas.
Hemorrhoids and Fissures: Chronic straining from constipation can cause painful hemorrhoids and anal fissures.

The role of fiber in a healthy digestive system

Fiber is an indigestible carbohydrate from plants that passes through your body mostly unchanged. It is categorized into two main types crucial for bowel function: soluble and insoluble fiber. Soluble fiber dissolves in water, forming a gel that helps soften stool and regulate digestion, blood sugar, and cholesterol. Insoluble fiber adds bulk and helps move waste through the intestines. Without sufficient amounts of both, your poop can change significantly.

Immediate consequences for your poop

Insufficient fiber intake quickly affects bowel movements, most commonly resulting in constipation. Stools become hard and small due to lack of water and bulk, making them difficult to pass. This leads to less frequent movements and increased straining, potentially causing hemorrhoids and anal fissures over time.

Long-term health implications beyond your poop

A low-fiber diet has effects beyond the immediate changes in stool. It harms the gut microbiome by starving beneficial bacteria that feed on fiber, leading to an imbalance called dysbiosis. This can weaken the intestinal barrier, increasing inflammation and susceptibility to infections. Chronic inflammation linked to a low-fiber diet is associated with a higher risk of heart disease, type 2 diabetes, and certain cancers.

Comparison of high-fiber vs. low-fiber poop

Here is a comparison of how fiber intake affects bowel movements:


Characteristic	High-Fiber Diet	Low-Fiber Diet
Consistency	Soft, formed, and easy to pass	Hard, dry, and difficult to pass
Frequency	Regular, at least one bowel movement daily	Irregular and infrequent, sometimes less than three times per week
Bulk/Size	Bulky, well-formed stools	Small, pebble-like stools
Color/Appearance	Varies depending on diet, often includes visible plant fibers	Can be dark and compact; lacks fibrous material
Effort	Little to no straining needed	Requires straining, potentially causing hemorrhoids or fissures
Smell	Usually less pungent due to healthier bacterial fermentation	Stronger and more foul odor due to putrefaction in the colon

How to get your poop back on track

To improve poop problems caused by low fiber, gradually increase fiber intake from food. Introduce high-fiber foods slowly to avoid gas and bloating. Drink plenty of water, as it's needed for fiber to work effectively. Focus on whole plant foods like fruits with skin, vegetables, whole grains, legumes, and nuts and seeds.

Conclusion

The condition of your poop is a key indicator of your dietary fiber intake. Insufficient fiber leads to uncomfortable, hard, and infrequent bowel movements. Furthermore, a long-term low-fiber diet negatively impacts gut bacteria, weakens the intestinal lining, and contributes to chronic inflammation linked to serious diseases. By gradually increasing fiber from whole plant foods and staying hydrated, you can improve digestive health. A high-fiber diet supports a healthy gut microbiome, comfortable elimination, and overall well-being. Consult a healthcare professional for personalized dietary advice. You can find more information about dietary fiber and gut health on reputable medical websites.

Frequently Asked Questions

The effects of low fiber can be noticed quite quickly, often within a few days of reduced intake. Your bowel movements may become less frequent, and your stools may feel harder and more difficult to pass.

Yes, while constipation is the more common symptom, low fiber can cause diarrhea. Certain types of fiber help form bulk and solidify stools. If undigested food moves through the system too quickly due to a lack of fibrous bulk, diarrhea can occur.

Yes, it is possible to eat too much fiber, especially if you increase your intake too quickly. This can lead to gas, bloating, and cramping. It's best to increase fiber gradually over several weeks to allow your digestive system to adapt.

Yes, drinking plenty of water is crucial, especially when increasing fiber intake. Fiber absorbs water to add bulk and soften stool, so without adequate fluid, constipation can worsen.

Excellent sources of fiber include whole grains like oats and brown rice, legumes such as beans and lentils, fruits (especially with the skin), vegetables, nuts, and seeds. Prioritizing a variety of these whole plant foods is the best strategy.

Fiber supplements, such as psyllium, can help, but it's generally best to get fiber from whole foods. Supplements lack the vitamins, minerals, and other nutrients found in natural food sources. Always consult a healthcare professional before starting supplements.

A low-fiber diet can starve the beneficial bacteria in your gut that use fiber for energy. This can lead to an imbalance in the microbiome (dysbiosis) and weaken the protective mucus barrier of your intestines.