How is resistant starch digested?

January 13, 2026 •

2 min read

Unlike regular starches that are quickly broken down in the small intestine, resistant starch is defined as starch that resists digestion in this part of the gut. It passes through the digestive tract largely intact, reaching the large intestine where its unique digestion process provides significant health benefits.

Quick Summary

Resistant starch bypasses digestion in the small intestine, traveling to the colon where it is fermented by gut bacteria. This process produces beneficial short-chain fatty acids, fueling the colon and supporting a healthy gut microbiome.

Key Points

Bypasses Small Intestine: Resistant starch travels undigested through the stomach and small intestine, acting like dietary fiber.
Fermented in the Colon: In the large intestine, resistant starch is fermented by beneficial gut bacteria, serving as their primary food source.
Produces Short-Chain Fatty Acids: This fermentation creates crucial compounds like butyrate, propionate, and acetate that have systemic health benefits.
Butyrate Feeds Colon Cells: Butyrate is the main energy source for the cells lining the colon, helping to maintain a healthy gut barrier.
Improves Glycemic Control: By not releasing glucose in the small intestine, resistant starch prevents blood sugar spikes and can improve insulin sensitivity.
Supports Gut Microbiome Health: Acts as a prebiotic, fostering a thriving and diverse population of 'good' bacteria in the gut.
Reduces Inflammation: The SCFAs produced from fermentation possess anti-inflammatory properties that can benefit the gut and overall health.

The Journey of Resistant Starch Through the Gut

Resistant starch (RS) gets its name from its ability to resist the enzymatic breakdown that occurs with most other starches. This resistance is key to its role in gut health. The process of how resistant starch is digested can be broken down into two main stages: the path through the upper digestive tract and the fermentation in the large intestine.

Stage 1: Bypassing Digestion in the Small Intestine

When you eat foods containing resistant starch, it passes through the stomach and into the small intestine. Unlike digestible starches, resistant starch is not easily broken down by enzymes like amylase. This resistance is due to various factors depending on the type of RS:

Type 1 (RS1): Found in whole grains, seeds, and legumes, where starch is physically trapped.
Type 2 (RS2): Occurs in raw potatoes and unripe green bananas, where the starch is in a dense granular structure.
Type 3 (RS3): Created when cooked starchy foods are cooled, forming a less digestible crystalline structure.
Type 4 (RS4): A synthetic form of resistant starch.
Type 5 (RS5): Formed by starch-lipid complexes.

Due to these characteristics, resistant starch moves through the small intestine without being converted to glucose, thus not causing a significant rise in blood sugar.

Stage 2: Fermentation in the Large Intestine

Upon reaching the colon, resistant starch acts as a prebiotic, nourishing the beneficial bacteria in the gut microbiome. These bacteria ferment the resistant starch, breaking it down into new compounds.

The Production of Short-Chain Fatty Acids (SCFAs)

The fermentation of resistant starch primarily produces short-chain fatty acids (SCFAs), such as butyrate, propionate, and acetate. These SCFAs offer several health advantages:

Butyrate: A primary energy source for colon cells, supporting gut barrier function and potentially reducing inflammation and cancer risk.
Propionate: Travels to the liver and may influence glucose and cholesterol metabolism.
Acetate: The most prevalent SCFA, used as fuel by various body tissues.

Fermentation also lowers colonic pH, promoting beneficial bacteria growth and inhibiting harmful ones. This process is generally less gas-producing compared to rapidly fermented fibers.

Resistant Starch vs. Digestible Starch

Understanding how resistant starch is digested is clearer when contrasted with digestible starch. The key differences are:


Feature	Resistant Starch	Digestible Starch
Digestion Site	Large intestine fermentation.	Stomach and small intestine digestion.
Resulting Compounds	SCFAs (butyrate, propionate, acetate).	Glucose.
Blood Sugar Impact	Minimal effect, supports glycemic control.	Rapid spike in blood sugar.
Caloric Value	Lower (approx. 2 kcal/g).	Higher (approx. 4 kcal/g).
Primary Function	Prebiotic, gut health.	Energy source.

Conclusion

Resistant starch follows a unique digestive path, resisting digestion in the upper gut and undergoing fermentation by colon bacteria. This fermentation yields beneficial SCFAs, which are vital for colon health and influence systemic metabolic processes. Including diverse types of resistant starch in your diet can contribute to a healthy gut and overall well-being. For further details, refer to resources like the CSIRO.

Frequently Asked Questions

Resistant starch passes through the small intestine largely undigested because it is inaccessible to the enzymes that break down most carbohydrates. It behaves more like a soluble fiber at this stage.

The primary products are short-chain fatty acids (SCFAs), including butyrate, propionate, and acetate. These are created when gut bacteria ferment the resistant starch in the large intestine.

Type 3 resistant starch (retrograded starch) is formed when starchy foods like potatoes, pasta, and rice are cooked and then cooled. This process makes the starch more resistant to digestion.

Resistant starch acts as a prebiotic, serving as food for beneficial gut bacteria. This fermentation promotes the growth of these 'good' bacteria and supports a healthy gut microbiome.

No, because resistant starch bypasses digestion in the small intestine, it does not get converted into glucose and absorbed into the bloodstream. This helps stabilize blood sugar levels.

Reheating cooled starchy foods can modestly increase or change the resistant starch content, but it does not completely destroy it. The exact effect can depend on the food and cooking method.

Resistant starch is technically a type of starch, but it functions similarly to dietary fiber in the body. It resists digestion in the small intestine and is fermented in the large intestine, just like many fermentable fibers.