Can Complex Carbs Cause Constipation? The Surprising Link to Gut Health

November 17, 2025 •

4 min read

Most Americans fail to consume the recommended daily amount of fiber, a key component of complex carbohydrates. This leads many to wonder: can complex carbs cause constipation? In reality, the issue isn't typically with complex carbs themselves, but with the type you choose and how you consume them.

Quick Summary

Complex carbohydrates, especially from whole-food sources, are rich in fiber that promotes healthy bowel function and prevents constipation. In contrast, refined carbs lack this crucial fiber and can slow digestion, contributing to irregularity. Proper hydration is essential when increasing fiber intake.

Key Points

Fiber is Key: The fiber in complex carbohydrates from whole foods is crucial for preventing constipation, not causing it.
Refined vs. Complex: Refined carbs, which lack fiber, are the more likely dietary culprit behind constipation due to slower digestion.
Hydration is Essential: Increasing your fiber intake from complex carbs requires a corresponding increase in water to prevent bloating and blockages.
Gradual Increase is Best: Introduce high-fiber complex carbs slowly into your diet to give your body time to adjust and avoid temporary digestive issues.
Resistant Starch Promotes Regularity: Specific starches in complex carbs like beans and oats feed healthy gut bacteria and add bulk to stool.
Check for Sensitivities: If constipation persists, consider potential intolerances like gluten sensitivity or conditions like IBS, which can be triggered by certain carbs.

The Truth About Complex Carbs and Digestion

Complex carbohydrates have a long and storied history in the world of nutrition. Once demonized, they have since been recognized as a cornerstone of a healthy diet, particularly for their role in providing sustained energy and—most importantly—for their positive impact on digestive health. However, confusion persists, especially for those experiencing bowel issues. The truth is, high-fiber complex carbohydrates are more likely to prevent constipation than cause it.

Complex vs. Refined Carbs: The Critical Difference

The key to understanding how carbs affect your bowel movements lies in distinguishing between complex and refined varieties. The processing of grains to create refined carbs, such as white flour and white rice, removes the bran and germ. These are the very components that contain the dietary fiber essential for healthy digestion. Complex carbs, conversely, are found in whole foods like vegetables, whole grains, and legumes, and they retain their natural fiber content.

When you consume refined carbs, you are essentially eating starchy foods with minimal fiber. This can cause digestion to slow down, potentially leading to constipation. Whole grains, on the other hand, provide a powerful combination of soluble and insoluble fiber that promotes regularity.

The Role of Fiber in Preventing Constipation

Fiber, a type of complex carbohydrate your body cannot digest, is the primary driver of healthy bowel function. It works in two main ways:

Insoluble Fiber: Often called 'roughage,' insoluble fiber adds bulk to your stool, which helps speed up its movement through your digestive tract. Good sources include whole wheat, nuts, and many vegetables.
Soluble Fiber: This type of fiber dissolves in water to form a gel-like substance that helps soften stool. It is found in oats, beans, apples, and peas. This softer stool is easier to pass, reducing straining and discomfort.

Working together, these two types of fiber create a powerful defense against constipation. A diet rich in a variety of complex carbs ensures you get both types of fiber, providing comprehensive support for your digestive system.

Resistant Starch and Gut Health

Another component of many complex carbs that benefits digestion is resistant starch. As the name suggests, resistant starch is a type of starch that resists digestion in the small intestine and instead ferments in the large intestine. This fermentation process feeds the beneficial bacteria in your gut, also known as your microbiome.

Benefits of Resistant Starch:
- Promotes the growth of good gut bacteria.
- Produces short-chain fatty acids that support colon health.
- Adds bulk to stool, helping to ease constipation.

Resistant starch is found in foods like lentils, beans, and oats. It can also be created by cooking and then cooling certain starchy foods, such as rice or potatoes.

Common Complex Carb Constipation Culprits and Solutions

While complex carbs are generally beneficial, there are scenarios where they can be associated with constipation. Understanding these can help you manage your digestive health effectively.


Cause of Constipation	Refined Carbs	Fiber-Rich Complex Carbs
Mechanism	Lack of fiber slows down digestion and can lead to hardened stool.	Usually beneficial. However, a rapid increase in fiber can cause bloating, gas, and temporary constipation if not accompanied by enough fluids.
Associated Foods	White bread, white pasta, white rice, sugary baked goods, processed snacks.	In some individuals, particularly those with conditions like IBS, high FODMAP (fermentable carbs) foods like certain whole grains or legumes can trigger symptoms.
Fluid Intake	Not a primary concern, but dehydration can worsen constipation regardless of diet.	High fiber intake requires increased fluid consumption. Without enough water, fiber can be less effective and even worsen constipation.
Underlying Issues	Can contribute to chronic constipation due to poor nutrient and fiber content.	Those with celiac disease or gluten sensitivity may experience constipation from gluten-containing grains like wheat and barley.

How to Avoid Constipation with Complex Carbs

Increase Fiber Gradually: If your diet has been low in fiber, introduce more complex carbs slowly to allow your digestive system to adjust. A sudden large increase can lead to temporary discomfort. Start by swapping out one refined grain per day for a whole-grain alternative.
Stay Hydrated: Water is essential for fiber to work effectively. Aim for at least 8-10 glasses of water per day, and increase your intake as you increase your fiber consumption.
Choose a Variety of Sources: Don't rely on a single source for your complex carbs. Incorporate a mix of whole grains (oats, brown rice, quinoa), legumes (beans, lentils), and vegetables (sweet potatoes, leafy greens) to ensure a balanced intake of different fibers.
Listen to Your Body: If you have known digestive conditions like Irritable Bowel Syndrome (IBS), some complex carb sources, like certain high-FODMAP foods, may exacerbate your symptoms. Pay attention to how your body reacts and consult a healthcare professional or dietitian if you suspect an intolerance.

Conclusion: A Healthy Gut Loves Whole-Food Carbs

The idea that complex carbs cause constipation is a common misconception. For most people, the opposite is true: the fiber-rich nature of whole-food complex carbohydrates is vital for preventing and relieving constipation. By favoring these nutritious sources over their refined counterparts and ensuring you drink enough water, you can promote a healthy and regular digestive system. If you suspect an underlying condition or experience persistent constipation, it is always wise to consult a healthcare provider.

For more information on balancing carbohydrates in your diet for optimal health, consult the American Heart Association's guide on carbohydrates.

Frequently Asked Questions

This can happen if you increase your fiber intake too quickly without also increasing your fluid consumption. High fiber draws water into the gut, and without enough water, it can cause stool to become dry and hard, leading to temporary constipation.

No, this is a myth. Complex carbohydrates, which are high in fiber, are beneficial for preventing constipation. It is typically refined carbs, stripped of their fiber, that contribute to constipation.

A variety is best. Good options include oats, legumes (beans, lentils), whole wheat products, quinoa, and many vegetables like sweet potatoes. Combining different sources provides a mix of soluble and insoluble fiber for optimal results.

For individuals with celiac disease or a gluten sensitivity, consuming gluten can damage the gut and lead to constipation. However, for most people, gluten-containing whole grains like whole wheat are excellent sources of fiber.

Yes, hydration is critically important. Water is needed for fiber to move through your digestive system effectively. Without sufficient fluid, the added bulk from fiber can have the opposite effect and worsen constipation.

Resistant starch is a type of complex carb that ferments in your large intestine, feeding beneficial gut bacteria. This process produces short-chain fatty acids and helps add bulk and softness to your stool, promoting regular bowel movements.

If you are prone to constipation, you should reduce your intake of foods like white bread, white rice, white pasta, and sugary baked goods, as these are low in fiber and can slow down digestion.