Is Starch Classified as a Dietary Fiber?

November 27, 2025 •

4 min read

According to the Food and Drug Administration, dietary fiber includes naturally occurring fibers in plants and certain isolated or synthetic non-digestible carbohydrates. Understanding this is key to answering the question: is starch classified as a dietary fiber? While most starches are quickly digested into glucose, a specific type of starch, known as resistant starch, is not.

Quick Summary

This article explores the key differences between regular starch and resistant starch regarding their digestion and function in the body. It clarifies how resistant starch meets the physiological definition of dietary fiber due to its indigestible nature and fermentability in the colon, distinguishing it from most other starches.

Key Points

Regular Starch vs. Fiber: The majority of dietary starch is rapidly digested for energy, unlike fiber, which is largely indigestible and passes through the small intestine intact.
Resistant Starch is a Fiber: A specific portion of starch, known as resistant starch, is not digested in the small intestine, and therefore functions physiologically like dietary fiber.
Prebiotic Function: Resistant starch is fermented by beneficial bacteria in the large intestine, acting as a prebiotic that produces health-promoting short-chain fatty acids.
Health Benefits: Like soluble fiber, resistant starch can improve gut health, enhance insulin sensitivity, and help regulate blood sugar levels.
Food Sources: You can increase your intake of resistant starch by consuming foods like legumes, green bananas, and cooked and cooled starchy foods such as potatoes and rice.
Digestive Differences: The key difference lies in how the body processes these carbohydrates; regular starch is broken down for energy, while resistant starch passes through, feeding gut microbiota instead.

What is Starch?

Starch is a complex carbohydrate found in plants, serving as a storage form of energy. It is composed of long chains of glucose units linked together. Foods like potatoes, rice, pasta, and bread are staple sources of starch in many diets. During digestion, enzymes in the small intestine, primarily amylase, break down most starches into glucose, which the body then uses for energy.

The Digestible Nature of Most Starch

Most starch is readily broken down and absorbed by the body. However, the exact rate of digestion can vary depending on the food source and preparation. For example, rapidly digestible starch (RDS) is found in cooked, readily consumed foods like fresh bread, while slowly digestible starch (SDS) has a more complex structure that takes longer to break down. The primary defining characteristic of these starches is that they are ultimately converted into absorbable energy for the body, a process that is fundamentally different from how the body handles fiber.

The Concept of Dietary Fiber

Dietary fiber consists of the non-digestible components of plant foods that pass largely intact through the human digestive system. Unlike starches and sugars, fiber is not broken down into glucose by human digestive enzymes. Instead, it travels to the large intestine, where it provides benefits to gut health. There are two primary types of dietary fiber:

Soluble Fiber: This type dissolves in water to form a gel-like material. It helps to lower blood cholesterol and glucose levels and is found in foods like oats, peas, beans, and apples.
Insoluble Fiber: This fiber does not dissolve in water. It adds bulk to stool and promotes the movement of material through the digestive system, which aids in preventing constipation. Sources include whole-wheat flour, nuts, and vegetables like cauliflower and green beans.

The Special Case of Resistant Starch

Here lies the nuance that directly addresses the article's central question. While regular starch is not fiber, a unique portion called resistant starch (RS) functions physiologically like dietary fiber. Resistant starch resists digestion in the small intestine and travels to the large intestine, where it is fermented by gut bacteria. The fermentation of RS by the gut microbiome produces beneficial compounds called short-chain fatty acids (SCFAs), which support gut health.

Types of Resistant Starch

Resistant starch isn't a single substance but a classification with several types, which is why it can be confusing. The four main types include:

RS1: Physically inaccessible starch. Found in whole or partially milled grains and seeds, where the starch is trapped within cell walls.
RS2: Native, granular starch. Present in uncooked starch granules, such as those in raw potatoes and green bananas.
RS3: Retrograded starch. Formed when starchy foods like rice or potatoes are cooked and then cooled. This process alters the structure, making it resistant to digestion.
RS4: Chemically modified starch. This is a synthetic type of resistant starch created for commercial food applications.

Comparison Table: Starch vs. Dietary Fiber


Feature	Regular Starch	Dietary Fiber	Resistant Starch (a subset)
Digestion	Easily broken down into glucose in the small intestine.	Not digested in the small intestine.	Resists digestion in the small intestine.
Function	Provides energy (glucose) to the body.	Adds bulk, regulates blood sugar, lowers cholesterol, and feeds gut bacteria.	Ferments in the large intestine, feeding gut bacteria and producing beneficial SCFAs.
Chemical Linkages	Contains α-(1→4) and α-(1→6) glycosidic bonds that human enzymes can break.	Contains β-(1→4) or other linkages that human enzymes cannot break.	Contains linkages and physical structures that resist enzymatic breakdown.
Caloric Value	Approximately 4 calories per gram.	Zero or very low calories (often stated as zero for labeling purposes).	Very low caloric value because it's not absorbed for energy.
Common Sources	Bread, pasta, rice, potatoes.	Whole grains, fruits, vegetables, legumes, nuts, seeds.	Green bananas, cooked and cooled potatoes/rice, legumes.

Health Benefits of Resistant Starch

The physiological effects of resistant starch align closely with the benefits of dietary fiber. By fermenting in the large intestine, resistant starch boosts the production of SCFAs, particularly butyrate, which is a primary fuel source for the cells lining the colon. This supports the integrity of the gut wall and helps protect against gastrointestinal diseases. Additionally, resistant starch consumption has been linked to improved insulin sensitivity and better blood sugar control, similar to soluble fiber. Its prebiotic nature also supports a healthy and diverse gut microbiome.

How to Increase Your Intake of Resistant Starch

Increasing your intake of resistant starch can be a straightforward process, often achieved by making small changes to your food preparation and eating habits. Cooking and then cooling certain starchy foods, such as potatoes, rice, and pasta, can increase their resistant starch content. Eating legumes like lentils and chickpeas is another excellent way to boost your intake. Lastly, incorporating green, unripe bananas into smoothies provides a natural source of resistant starch.

Conclusion: A Clear Distinction

To conclude, is starch classified as a dietary fiber? For the most part, no, it is not. The majority of starches are digestible carbohydrates that provide energy. However, a specific fraction known as resistant starch behaves functionally like dietary fiber because it resists digestion in the small intestine and is fermented in the large intestine. This physiological behavior, and the resulting health benefits, is why some dietary definitions now include resistant starch under the broader umbrella of fiber. Understanding this distinction is crucial for making informed dietary choices that promote better digestive health and overall well-being. For a deeper understanding, consulting sources like the CSIRO on resistant starch can provide further insight.

Frequently Asked Questions

The primary difference is digestibility. Most starch is easily broken down by the body's enzymes into glucose for energy. In contrast, fiber is a non-digestible carbohydrate that passes largely intact through the digestive system.

Resistant starch is considered a type of fiber because it 'resists' digestion in the small intestine, just like fiber. It then travels to the large intestine, where it is fermented by gut bacteria, providing similar health benefits.

All starchy foods contain resistant starch to some degree, but the amount varies significantly. For example, a cooked and cooled potato has more resistant starch than a freshly cooked one. The best sources are legumes, green bananas, and cooked and cooled grains.

Resistant starch passes through the small intestine without being broken down. In the large intestine, it is fermented by the gut microbiota, which produces beneficial compounds called short-chain fatty acids (SCFAs) that nourish the colon lining.

Yes, you can. Simple methods include cooling cooked rice, potatoes, or pasta before eating them. You can also incorporate more legumes, like lentils and chickpeas, and have green bananas.

Yes. Because resistant starch resists digestion, it does not cause a rapid rise in blood sugar levels like regular starches. It can actually help improve insulin sensitivity and support better glucose control.

Resistant starch is a type of fermentable carbohydrate that acts similarly to soluble fiber by feeding gut bacteria. However, it is structurally a modified starch rather than a traditional soluble fiber like pectin or guar gum.

It is important because not all carbohydrates are processed equally by the body. While most starches provide absorbable energy, resistant starch behaves like fiber and offers distinct gut health benefits, highlighting the importance of looking beyond just 'total carbohydrates' on a nutrition label.