What is not a digestible carbohydrate found in food?

December 28, 2025 •

4 min read

According to the U.S. National Academy of Medicine, most Americans consume less than 50% of the recommended daily amount of fiber, a key example of an indigestible carbohydrate. These carbohydrates pass through our digestive system largely intact, playing a vital and often overlooked role in human health.

Quick Summary

This article explains indigestible carbohydrates, such as dietary fiber and resistant starch, which are not broken down by human enzymes. It covers their sources, types, and crucial functions in promoting digestive health and nourishing gut bacteria.

Key Points

Dietary Fiber: The body lacks the enzymes to digest dietary fiber, which is a key non-digestible carbohydrate found in plants like whole grains and legumes.
Resistant Starch: Starches like those in uncooked potatoes and cooled pasta can resist digestion in the small intestine and function as a prebiotic in the colon.
Prebiotics: Many indigestible carbohydrates, including certain fibers and resistant starches, act as prebiotics, selectively feeding and promoting the growth of beneficial gut bacteria.
Two Main Types: Indigestible carbohydrates are primarily categorized as soluble fiber, which forms a gel, and insoluble fiber, which adds bulk to stool, with most plant foods containing a mix of both.
Health Benefits: Instead of providing calories, these carbs are fermented in the large intestine to produce short-chain fatty acids, supporting digestive health, mineral absorption, and overall wellness.
Different Digestion: Unlike digestible carbohydrates that break down into simple sugars and are absorbed, indigestible ones pass to the large intestine to be fermented by microbes.

Understanding Indigestible Carbohydrates

Indigestible carbohydrates are complex sugar polymers that the human body cannot break down using its own digestive enzymes. Instead of being absorbed and used for energy like other carbohydrates, they pass through the stomach and small intestine to the large intestine. Here, they are fermented by gut bacteria, where they provide several health benefits. The primary examples of these non-digestible carbohydrates are dietary fiber and resistant starch, though the broader category also includes prebiotics and certain sugar alcohols.

The Role and Types of Dietary Fiber

Dietary fiber is arguably the most well-known type of indigestible carbohydrate. It is derived from plant foods and is classified into two main types based on its solubility in water: soluble and insoluble fiber. Both types are essential for a healthy diet and perform different but complementary functions in the body.

Soluble Fiber: This type of fiber dissolves in water to form a gel-like substance. It helps slow down digestion, which can assist in controlling blood sugar levels and lowering cholesterol. Foods rich in soluble fiber include oats, barley, nuts, seeds, beans, lentils, peas, and some fruits like apples and blueberries.
Insoluble Fiber: Insoluble fiber does not dissolve in water. It adds bulk to stool and helps food pass more quickly through the digestive system, promoting regularity and preventing constipation. Good sources of insoluble fiber include whole wheat, wheat bran, brown rice, and vegetables such as cauliflower and green beans.

Resistant Starch: A Carb That Acts Like Fiber

Resistant starch is another category of carbohydrate that escapes digestion in the small intestine, functioning similarly to dietary fiber. It is fermented by gut bacteria in the large intestine, where it produces short-chain fatty acids (SCFAs), which provide energy for the colon cells and offer numerous health benefits. There are several types of resistant starch (RS):

RS Type 1: Physically inaccessible starch found in whole grains and seeds.
RS Type 2: Native granular starch found in raw potatoes and unripe bananas.
RS Type 3: Retrograded starch that forms when starchy foods like potatoes and pasta are cooked and then cooled.
RS Type 4: Chemically modified starch created for industrial purposes.

Prebiotics and the Gut Microbiome

Prebiotics are a type of fermentable, non-digestible carbohydrate that selectively nourishes beneficial bacteria in the gut. This process of feeding the gut flora is critical for maintaining a healthy and diverse microbiome, which has far-reaching effects on overall health, including immune function and nutrient absorption. Many types of fiber and resistant starch function as prebiotics. Foods rich in prebiotics include chicory root, garlic, onions, and asparagus.

The Importance of Indigestible Carbs for Health

Despite not providing direct caloric energy, indigestible carbohydrates are crucial for many aspects of human health. Their fermentation in the colon produces short-chain fatty acids (SCFAs) which are linked to a host of benefits, from reducing inflammation to improving mineral absorption. A diet rich in these compounds supports a balanced gut microbiome, which is associated with better digestive regularity, improved blood sugar control, and a reduced risk of chronic diseases like heart disease and certain cancers.

Comparison of Digestible and Indigestible Carbohydrates


Feature	Digestible Carbohydrates	Indigestible Carbohydrates
Primary Function	Energy source for the body	Promotes gut health, adds bulk to stool, and nourishes gut flora
Digestion	Broken down by human digestive enzymes (e.g., amylase) in the mouth and small intestine.	Passes largely intact through the small intestine; fermented by bacteria in the large intestine.
Absorption	Absorbed as simple sugars (monosaccharides) into the bloodstream.	Not absorbed; provides no direct calories but produces beneficial compounds like SCFAs.
Effect on Blood Sugar	Rapidly raises blood sugar levels, especially simple carbs.	Slows sugar absorption, which helps to stabilize blood glucose levels.
Sources	White bread, table sugar, sweets, potatoes, white rice, ripe bananas.	Whole grains, vegetables, fruits, legumes, unripe bananas, cooked and cooled pasta and potatoes.

Conclusion

In conclusion, while digestible carbohydrates like glucose and starch provide the body with essential energy, carbohydrates that are not digestible, such as dietary fiber and resistant starch, play a profoundly important and distinct role in maintaining overall health. These compounds, which include powerful prebiotics, serve as fuel for beneficial gut bacteria, facilitate regular digestion, and contribute to the prevention of chronic disease. Embracing a diet rich in a variety of plant-based foods, including whole grains, legumes, fruits, and vegetables, is the best way to ensure an adequate intake of these crucial nutrients, supporting not just digestive wellness but the entire body. For further reading, the National Institutes of Health provides extensive research on the health effects of indigestible carbohydrates.

Frequently Asked Questions

Indigestible carbohydrates are not broken down by the enzymes in the stomach or small intestine. They travel to the large intestine where they are fermented by beneficial bacteria, a process that produces short-chain fatty acids.

No, dietary fiber does not provide calories directly to the body. While fermentation in the large intestine produces some energy in the form of short-chain fatty acids, fiber itself is not a source of caloric energy in the same way as other carbs, proteins, or fats.

Yes, dietary fiber is, by definition, the indigestible part of plant foods. Both soluble and insoluble fiber pass through the human digestive system without being broken down by human enzymes.

Foods containing resistant starch include unripe bananas, legumes like beans and lentils, whole grains, and starchy foods like potatoes and pasta that have been cooked and then cooled.

Fermentation of these carbohydrates by gut bacteria is important because it nourishes the gut microbiome and produces beneficial short-chain fatty acids. These fatty acids help maintain a healthy gut lining and can have systemic anti-inflammatory effects.

Prebiotics are the indigestible carbohydrates that serve as food for good bacteria in your gut. Probiotics are the live, beneficial bacteria themselves, often consumed through fermented foods or supplements.

You can increase your intake by eating more whole grains, fruits, vegetables, legumes, and nuts. Choosing minimally processed versions of these foods and incorporating cooked and cooled starches can also help.

As bacteria in the large intestine ferment indigestible carbohydrates, they can produce gas as a byproduct. Increasing fiber intake gradually and drinking plenty of water can help minimize discomfort like bloating.