When most people hear the word starch, they think of potatoes, rice, pasta, or bread. Starch is one of the main sources of energy in our diet, and under normal circumstances, our body breaks it down into glucose, which it uses as fuel for cells.
However, there is also a special form of starch that behaves quite differently. It is called resistant starch (Resistant Starch – RS). Unlike regular starch, it is not digested in the small intestine but passes through to the large intestine, where it becomes a source of nourishment for the gut microbiome.
This is precisely why resistant starch has been receiving increasing attention in scientific circles and nutrition in recent years. Research shows that it is not simply an ordinary carbohydrate, but a food component with unique properties that belongs among the prebiotic forms of dietary fiber.
Today, we know several types of resistant starch (RS1 to RS5), which differ in their origin, structure, and behavior in the digestive tract. Some occur naturally in grains, legumes, or green bananas, while others are formed by cooling cooked foods such as potatoes or rice.
In this article, we will look at:
By the end of the article, you will have a clear understanding of what resistant starch is, where you can find it, and why it is receiving increasing attention from scientists and nutrition experts.
Resistant starch is a special type of starch that behaves differently from the regular starch found in food. While most starches are broken down into glucose in the small intestine and serve as a source of energy, resistant starch resists this digestion. This is where its name comes from – resistant, meaning resistant to the action of digestive enzymes.
This means that it passes through the digestive tract almost unchanged until it reaches the large intestine. There, it becomes a source of nutrients for intestinal microorganisms, which gradually ferment it. This property distinguishes resistant starch from regular starches and places it among the prebiotic components of the diet.
Not all starch is the same
The word starch is often used as a general term, but in reality there are significant differences between individual types of starch. How starch behaves in our body depends on its chemical structure, the way the food is processed, and the source itself.
Regular starch is rapidly or gradually broken down into simple sugars after consumption, which are then absorbed into the bloodstream. Resistant starch, however, escapes digestion by digestive enzymes and continues on to the large intestine, where it performs a completely different role.
This is why scientific literature distinguishes three basic groups of starch:
| Type of starch | What happens to it in the body |
|---|---|
| Rapidly digestible starch (RDS) | It is digested quickly and rapidly increases blood glucose levels. |
| Slowly digestible starch (SDS) | It is digested more gradually, and glucose is released more slowly. |
| Resistant starch (RS) | It is not digested in the small intestine and reaches the large intestine. |
Resistant starch is currently the subject of intensive scientific research. Scientists are particularly interested in its interaction with the gut microbiome, as it provides a source of nutrients for certain beneficial intestinal bacteria.
Why is resistant starch interesting?
In the past, starch was viewed primarily as a source of energy. Today, however, we know that not all starch behaves in the same way. Resistant starch is an exception – instead of being broken down into glucose in the small intestine, it continues on to the large intestine.
This property distinguishes it from most carbohydrates in our diet and explains why it is receiving increasing attention from nutrition experts and scientists studying the gut microbiome.
Resistant starch occurs naturally in certain foods, such as green bananas, legumes, and certain types of grains. Its content can also change during food processing. For example, after potatoes, rice, or pasta are cooked and subsequently cooled, some of the regular starch is converted into resistant starch – a process known as starch retrogradation.
Although we often simply refer to resistant starch, it is actually not a single substance. Scientists distinguish five types of resistant starch (RS1–RS5), which differ in their origin, structure, and the way they resist digestion.
A common characteristic of all types is that they are not completely or at all digested in the small intestine. The difference lies in why they are resistant to digestive enzymes.
RS1 – physically protected starch
RS1 is enclosed inside plant cells, preventing digestive enzymes from reaching it. It is found mainly in:
When these foods are thoroughly ground or extensively cooked, their protective structure is disrupted and some RS1 may become digestible.
RS2 – naturally resistant starch
RS2 has a specific crystalline structure that naturally resists digestion.
Its best-known sources include:
RS2 is currently the most extensively studied type of resistant starch and has been the subject of several clinical studies focusing on the gut microbiome and prebiotic properties.
RS3 – retrograded starch
RS3 is formed after starchy foods have been cooked and subsequently cooled.
Typical examples include:
After cooling, some of the starch rearranges into a new structure that is more resistant to digestion. This natural process is called starch retrogradation.
RS4 – chemically modified starch
RS4 does not occur naturally. It is starch that has been modified through chemical or technological processes in order to alter its properties.
It is used primarily in the food industry, for example to improve the texture or stability of products.
RS5 – starch bound to fats
RS5 is the most recently discovered type. It forms through the association of starch molecules with certain fats, creating complexes that are more resistant to digestion.
Research into RS5 is still relatively new, and scientists continue to investigate its properties and potential applications in nutrition.
Overview of resistant starch types
| Type | How it is formed | Typical sources |
|---|---|---|
| RS1 | Physically enclosed within plant cells | Whole grains, seeds, legumes |
| RS2 | Naturally occurring crystalline structure | Raw potatoes, green bananas, high-amylose corn |
| RS3 | Formed after cooking and subsequent cooling | Potatoes, rice, pasta, oats |
| RS4 | Chemical modification of starch | Some industrially processed foods |
| RS5 | Binding of starch with fats | Formed during specific technological processes |
Which type is the most extensively studied?
Although each type of resistant starch has its place in nutrition, the greatest amount of scientific research currently focuses on RS2. This is due to its natural origin, stable structure, and the possibility of standardized use in scientific studies.
For this reason, most modern research focusing on resistant starch, the gut microbiome, and prebiotic properties is devoted specifically to this form.
To understand why resistant starch is so unique, it is useful to look at its journey through the digestive tract. Unlike regular starch, it does not finish its “role” in the small intestine but continues further to where one of the most interesting processes in our body begins – its interaction with the gut microbiome.
Starch digestion begins in the mouth. The enzyme salivary amylase starts breaking down regular starch into smaller components. However, this process lasts only briefly because food quickly moves into the stomach.
Resistant starch behaves differently even at this stage. Its structure is so resistant that enzymes have only minimal or no effect on it.
In the stomach, food is mixed with gastric juices. The main role of the stomach is protein digestion, so starch is hardly broken down here.
Resistant starch remains almost unchanged and continues into the small intestine.
It is in the small intestine that the greatest difference between regular and resistant starch occurs.
Regular starch is broken down here by pancreatic enzymes into glucose, which is subsequently absorbed into the bloodstream and serves as a source of energy.
Resistant starch, however, resists this process. Digestive enzymes cannot completely break it down, so it passes through the small intestine largely intact.
This property is precisely why it is called resistant starch.
Upon reaching the large intestine, resistant starch encounters trillions of microorganisms that make up the gut microbiome.
Unlike human digestive enzymes, certain intestinal bacteria can ferment resistant starch. During this natural process, various metabolites are produced, including short-chain fatty acids (SCFAs), which we will discuss in more detail in the following chapter.
This is why resistant starch is considered a prebiotic – it provides nutrients for selected microorganisms in the large intestine.
The journey of resistant starch in brief
| Part of the digestive tract | What happens to resistant starch? |
|---|---|
| Mouth | Digestion of regular starch begins, while resistant starch remains almost unchanged. |
| Stomach | It passes through the acidic environment without significant change. |
| Small intestine | It resists digestive enzymes and is not absorbed as glucose. |
| Large intestine | It becomes a substrate for fermentation by intestinal bacteria. |
Why is this important?
It is precisely the ability to reach the large intestine that makes resistant starch a unique component of the diet. While most carbohydrates are utilized as a source of energy before reaching the large intestine, resistant starch becomes part of the environment in which the gut microbiome lives.
This is also why resistant starch is classified as a prebiotic component of the diet and why it is currently the subject of intensive scientific research.
Until a few decades ago, the intestines were viewed primarily as an organ responsible for digesting food and absorbing nutrients. Today, however, we know that their importance is much broader. Our digestive tract is home to a vast number of microorganisms that together form the gut microbiome.
The gut microbiome is one of the most extensively studied areas of modern medicine and nutrition. Scientists are trying to understand how the composition of intestinal bacteria affects the functioning of the body and what role diet plays in maintaining their balance.
What is the gut microbiome?
The gut microbiome is a community of billions of microorganisms that naturally inhabit our intestines. These include mainly bacteria, but also yeasts, viruses, and other microorganisms.
The largest number of these microorganisms is found in the large intestine, where they form an exceptionally complex ecosystem. Each person has a unique gut microbiome composition, much like a unique fingerprint.
The composition of the microbiome is influenced by many factors, such as:
The microbiome needs nourishment
Just as humans need nutrients, intestinal bacteria also need a source of energy. However, not all bacteria utilize the same substances.
Some microorganisms can utilize components of food that our own digestive enzymes cannot break down. One such substance is resistant starch.
Upon reaching the large intestine, resistant starch becomes a substrate for fermentation, during which intestinal bacteria gradually break it down. This natural process is one of the reasons why resistant starch is classified as a prebiotic.
Balance is more important than quantity
When discussing the gut microbiome, people often refer to “good” and “bad” bacteria. In reality, the situation is much more complex.
What matters is not only which bacteria are present in the gut, but also their balance and diversity. A diverse microbiome is one of the characteristics of a healthy intestinal environment.
Many factors can influence the composition of the microbiome, with daily diet being one of the most important.
Diet shapes the gut microbiome every day
What we eat affects not only us, but also the microorganisms living in our intestines.
Foods rich in fiber and other indigestible components provide intestinal bacteria with a source of nutrients. Conversely, a long-term monotonous diet low in fiber may result in microorganisms having fewer substrates available for fermentation.
For this reason, experts recommend regularly including a diverse range of foods naturally rich in fiber, including sources of resistant starch.
Why is the microbiome talked about so much today?
The development of modern genetic methods has enabled scientists to study the gut microbiome in much greater detail than in the past. Hundreds of new scientific publications are added every year examining the relationship between nutrition, intestinal bacteria, and the functioning of the body.
This is why increasing attention is also being paid to prebiotics, including resistant starch. Research focuses on how different types of fiber may influence the composition of the gut microbiome and which metabolites are produced during their fermentation.
One of the most important groups of these metabolites is short-chain fatty acids (SCFAs). In the following chapter, we will explain what they are, how they are produced, and why they are an integral part of resistant starch fermentation.
When resistant starch reaches the large intestine, its journey does not end. Quite the opposite – a process begins that is one of the main reasons why this form of fiber has been the subject of such intense discussion in recent years.
Certain intestinal bacteria are capable of fermenting resistant starch. This is a natural biological process in which microorganisms use indigestible components of food as a source of energy. Fermentation produces various substances, the best known of which are short-chain fatty acids, abbreviated as SCFAs (Short-Chain Fatty Acids).
These compounds are among the most extensively studied products of intestinal fermentation.
What are SCFAs?
SCFAs are naturally occurring fatty acids with short carbon chains. They are produced in the large intestine during the fermentation of fiber and other indigestible carbohydrates by intestinal bacteria.
The three most important are:
Their relative proportions may vary depending on the composition of the gut microbiome and the type of fiber being fermented.
Acetate
Acetate is the most abundant short-chain fatty acid. It is produced during the fermentation of various types of fiber and represents an important product of intestinal bacterial metabolism.
Once produced, it can be absorbed from the large intestine and naturally participates in the body’s metabolic processes.
Propionate
Propionate is another fatty acid produced during the fermentation of fiber.
After absorption, it is transported primarily to the liver, where it is further metabolized. This is why it is among the metabolites frequently studied in research on the gut microbiome and nutrition.
Butyrate
Butyrate is one of the best-known products of resistant starch fermentation.
It is produced by specific groups of intestinal bacteria and is one of the most extensively studied metabolites of the gut microbiome. Scientific publications examine its role in the functioning of the large intestine as well as its relationship with the intestinal environment.
Fermentation is a natural part of digestion
The word fermentation is often associated mainly with the production of yogurt or sauerkraut. The same principle, however, also takes place in our large intestine.
Intestinal bacteria use indigestible components of food as a source of energy. During this process, SCFAs and other substances are produced, which are natural components of the intestinal environment.
This is why experts recommend regularly consuming different types of fiber. Each type of fiber can be utilized by different groups of intestinal microorganisms, thereby contributing to the diversity of their nutritional sources.
Why is fiber diversity important?
In the past, fiber was often divided simply into soluble and insoluble fiber. Today, however, we know that individual types of fiber differ not only in their solubility, but also in how quickly they ferment and which bacteria can utilize them.
Resistant starch is one example of a type of fiber that reaches the large intestine and becomes part of the natural fermentation processes of the gut microbiome.
This is why it is recommended to consume fiber from a variety of sources – whole grains, legumes, fruit, vegetables, and foods containing resistant starch. A diverse diet provides intestinal bacteria with a broader spectrum of nutrients and supports the natural diversity of the gut microbiome.
In recent years, we have increasingly encountered the terms probiotics and prebiotics. Although they sound similar, they refer to two different things that complement each other.
Simply put, probiotics are live microorganisms, while prebiotics are food for selected beneficial microorganisms that are already naturally present in our intestines.
Resistant starch belongs to the group of prebiotics.
What is a prebiotic?
According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), a prebiotic is:
“A substrate that is selectively utilized by host microorganisms conferring a health benefit.”
In other words, it is a substance that humans cannot digest themselves, but which certain intestinal bacteria can utilize.
Resistant starch meets this definition because it passes through the digestive tract into the large intestine, where it becomes a substrate for fermentation by intestinal microorganisms.
What is the difference between probiotics and prebiotics?
These two terms are often confused, but their meanings are different.
| Probiotics | Prebiotics |
|---|---|
| Live microorganisms | Non-digestible components of food |
| Provide the body with beneficial bacteria | Provide nourishment for bacteria that already live in the gut |
| Found, for example, in fermented foods | Found in fiber, resistant starch, inulin, and other prebiotics |
The simplest way to think of it is:
Both groups play a role in nutrition and complement each other.
Not all prebiotics are the same
There are also differences among prebiotics. Some ferment very quickly, while others ferment more slowly. Some are soluble in water, while others are not. They also differ in which groups of intestinal bacteria are able to utilize them.
The best-known prebiotics include:
Each has its own specific properties, so they are not mutually exclusive. On the contrary, a varied diet containing different types of fiber provides the gut microbiome with a broader spectrum of nutrients.
Why is diversity important?
Imagine the gut microbiome as a large garden. If you continually water only one type of plant, the others will not thrive. The same applies to intestinal bacteria.
Different types of fiber represent different sources of nutrients for different groups of microorganisms. The more varied the diet, the more diverse the conditions it creates for the gut microbiome.
Therefore, experts recommend consuming fiber from multiple natural sources rather than relying on a single type.
Resistant starch as part of a varied diet
Resistant starch is one form of prebiotic fiber that naturally complements other sources of fiber in the diet. It does not replace vegetables, fruit, or whole grains, but it can be a suitable addition to them.
The combination of different types of fiber is currently considered a natural way to support a varied and balanced diet.
Resistant starch is neither a new nor an artificially created substance. It is a natural component of many foods that people have consumed for centuries. However, its amount can vary considerably depending on the type of food, degree of ripeness, and method of processing.
This is why two seemingly identical foods may sometimes contain completely different amounts of resistant starch.
One of the best-known natural sources of resistant starch is unripe green bananas.
During ripening, a large portion of the resistant starch is gradually converted into simpler sugars. Therefore, green bananas contain more resistant starch than fully ripe bananas with yellow or brown skins.
Potatoes naturally contain starch. In their raw state, they also contain resistant starch type RS2.
After cooking, its structure changes and some of the resistant starch becomes digestible. However, if cooked potatoes are allowed to cool, some of the starch rearranges into a more resistant structure and resistant starch type RS3 is formed.
This is why cooled potatoes may have different properties from freshly cooked potatoes.
A similar phenomenon can be observed with rice.
Freshly cooked rice contains less resistant starch than rice that has been cooled after cooking. During cooling, a natural process called starch retrogradation occurs, in which some of the starch is converted into a resistant form.
The same principle applies to pasta.
When pasta is cooled after cooking, some of the starch develops a more resistant structure. This is why pasta salads made with cooled pasta are a natural source of resistant starch type RS3.
Beans, lentils, chickpeas, and peas naturally contain fiber as well as a certain amount of resistant starch.
They are also rich in other components that are natural prebiotics, making them an important part of a varied diet.
Some whole grains contain resistant starch type RS1, which is enclosed inside plant cells. As long as the grain structure remains intact, digestive enzymes have only limited access to the starch.
Grinding or intensive processing, however, can reduce the amount of resistant starch.
How does food preparation affect the resistant starch content?
One of the interesting properties of resistant starch is that its amount can change during cooking and subsequent cooling.
The best-known examples are:
After cooking, most of the starch becomes easier to digest. However, if these foods are allowed to cool for several hours, some of the starch naturally rearranges into a more resistant structure. This process is called retrogradation and leads to the formation of resistant starch type RS3.
This is why cooled potatoes or rice are often discussed in connection with resistant starch content.
Overview of natural sources of resistant starch
| Food | Type of resistant starch |
|---|---|
| Green bananas | RS2 |
| Raw potatoes | RS2 |
| Cooled potatoes | RS3 |
| Cooled rice | RS3 |
| Cooled pasta | RS3 |
| Legumes | RS1 + naturally occurring resistant starch |
| Whole grains | RS1 |
Can you get enough resistant starch from food alone?
A varied diet is the foundation of a healthy lifestyle, and natural sources of resistant starch should have their place in the diet.
On the other hand, it is important to realize that the amount of resistant starch in foods is not constant. It is influenced by the variety, ripeness, processing method, and heat treatment. Therefore, actual intake from a regular diet can vary considerably.
For this reason, standardized sources of resistant starch have also emerged in recent years, allowing for more precise dosing and consistent content. One of these is type RS2 resistant potato starch, which we will discuss in more detail in the second article devoted to this topic.
The good news is that resistant starch can be incorporated into the diet relatively easily. There is no need to make radical changes or seek out exotic foods. Even small adjustments to the way food is prepared can naturally increase its intake.
Let some foods cool after cooking
One of the simplest ways is to prepare food in advance and allow it to cool after cooking. During cooling, some of the starch naturally changes into resistant starch type RS3.
This applies particularly to:
This is why potato or pasta salads are natural sources of resistant starch.
Include more legumes in your diet
Legumes are naturally rich in fiber and also contain resistant starch.
You can regularly include, for example:
In addition to resistant starch, they contain many other nutrients and represent an important part of a varied diet.
Don’t be afraid of whole grains
Whole grains retain their natural structure, which means they also contain resistant starch type RS1.
Suitable choices include:
Variety is important
There is no single “miracle” food that can provide everything the gut microbiome needs. Diversity is much more important.
A varied diet should contain:
Each of these foods provides different nutrients not only to humans, but also to intestinal microorganisms.
What if dietary intake is low?
In everyday life, it is not always easy to regularly consume enough foods rich in resistant starch. In addition, its content can vary considerably depending on the food variety, degree of ripeness, storage method, and heat treatment.
This is why standardized sources of resistant starch have been developed, allowing for a precisely defined content and easy incorporation into the daily diet.
These are most commonly fine powders without a pronounced taste or smell, which can easily be mixed into cold or lukewarm foods and beverages without significantly affecting their taste.
Practical tips
Resistant starch can easily be added to, for example:
For products containing resistant starch, it is always advisable to follow the manufacturer’s recommendations, as individual ingredients may differ in their properties and recommended method of use.
Start gradually
If you have previously consumed little fiber, it is advisable to increase your intake gradually. A sudden change may cause temporary digestive discomfort in some people, such as bloating or increased gas.
Adequate fluid intake and an overall varied, balanced diet are equally important.
What to remember from this article?
Resistant starch is a natural component of many foods and represents an interesting form of prebiotic fiber. Unlike regular starch, it is not digested in the small intestine but reaches the large intestine, where it becomes a substrate for fermentation by intestinal bacteria.
Today, we know five types of resistant starch (RS1 to RS5), which differ in their origin and properties. The best-known natural sources include green bananas, legumes, whole grains, and cooled potatoes, rice, and pasta.
Research into resistant starch is one of the dynamically developing areas of nutrition and gut microbiome research. Although scientists are intensively studying its effects, it is already clear that a varied diet containing sufficient amounts of different types of fiber remains one of the fundamental pillars of a healthy lifestyle.
Resistant starch is an example of how even familiar foods can contain properties that we did not know about until relatively recently. What was once considered merely ordinary starch is now the subject of intensive scientific research.
