Resistant starch acts more like fiber than starch—and may offer unique benefits for blood sugar, gut health, and more. In this episode, we break down the different types, where to find them, and how they compare to other sources of fiber.
Resistant starch acts more like fiber than starch—and may offer unique benefits for blood sugar, gut health, and more. In this episode, we break down the different types, where to find them, and how they compare to other sources of fiber.
Transcript: https://nutrition-diva.simplecast.com/episodes/resistant-starch-your-questions-answered/transcript
Mentioned in this episode:
Episode 915, Multi-grain vs whole grain
Episode 560, Fiber 2.0—Fiber's New Science of Health-Boosting Benefits
Episode 728, Tapping into the many benefits of resistant starches
References:
Wang, Y., Chen, J., Song, Y.-H., Zhao, R., Xia, L., Chen, Y., Cui, Y.-P., Rao, Z.-Y., Zhou, Y., Zhuang, W., & Wu, X.-T. (2019). Effects of the resistant starch on glucose, insulin, insulin resistance, and lipid parameters in overweight or obese adults: a systematic review and meta-analysis. PubMed. https://pubmed.ncbi.nlm.nih.gov/31168050/
Yuan, H. C., Meng, Y., Bai, H., Shen, D. Q., Wan, B. C., & Chen, L. Y. (2018). Meta-analysis indicates that resistant starch lowers serum total cholesterol and low-density cholesterol. PubMed. https://pubmed.ncbi.nlm.nih.gov/29914662/
Welcome to the Nutrition Diva podcast, where we take a closer look at nutrition news, research, and trends so you can feel more confident about what you eat. I’m your host, Monica Reinagel, and today’s episode was inspired by a question from Jerry, who wrote:
“While listening to your May 13th episode on multigrain versus whole grain, you briefly mentioned resistant starch. I’ve been seeing ‘resistant wheat starch’ listed in the ingredients of some high-fiber breads and I’d love to understand exactly what that is. How is that 12 grams of fiber per slice different from the fiber in, say, beans or oats?”
Such a great question; I was recently wondering the same thing: Does the fiber we get from products made with resistant starch provide the same benefits as fiber we might get from whole foods? And the answer is somewhat complex, because resistant starch isn’t just one thing. There are actually multiple types of resistant starch, each with slightly different properties. And they don’t all show up the same way in your diet—or on a food label.
So today, we’re going to take a closer look at the different types of resistant starch, how they compare to other types of fiber, and how you might include more of it in your diet—whether through your own cooking or by reading between the lines of packaged food labels.
Most of the starch we eat—what we might call “regular” starch—is made up of long chains of glucose molecules. Even though it’s essentially made of sugar, starch doesn’t actually taste sweet. That’s because in starch, those glucose molecules are locked together by bonds that need to be broken down by digestive enzymes before the glucose can be released and absorbed into the bloodstream.
Most of this happens in the small intestine. But your saliva also contains small amounts of an enzyme called amylase, which starts to break down starch the moment you begin chewing. I remember doing a fun experiment in fifth grade that demonstrated this in a very memorable way. You can even try it at home with your kids: Chew a plain-unsalted saltine cracker for long enough and it will start to taste faintly sweet. You’re literally tasting the starch being broken down into sugar on your tongue.
Resistant starch is also made of glucose molecules. But the bonds that hold the molecules together are resistant to those starch-digesting enzymes. So instead of being broken down into glucose molecules in the small intestine, it passes through to the large intestine intact.
Because it escapes digestion, resistant starch behaves more like fiber than starch. In fact, it’s officially classified as a type of dietary fiber–which is how you’ll find it listed on Nutrition Facts labels. But not all resistant starch is the same. In fact, there are several distinct types—each with its own characteristics, sources, and applications.
There are five generally recognized types of resistant starch. We’re going to focus primarily on RS2, RS3, and RS4, because these are the forms you’re most likely to come across. But just to round out the picture:
RS1 is found in whole or coarsely milled grains, legumes, or seeds. More finely milled products (like whole grain flour) will contain less RS1, because the physical barriers that make the starch resistant have been broken down. RS1 is generally heat stable (unaffected by cooking) and it would simply be included as part of the total dietary fiber.
RS5 is a newer and less well-known category of resistant starch. It forms when starch molecules bind with fats, creating a structure that resists digestion. These complexes can form naturally in foods that contain both starch and fat, especially during cooking. However, we don’t know a whole lot about how it might behave in the body. Because it’s still being studied, you’re unlikely to see RS5 mentioned on labels or used intentionally in food products—at least for now.
Now, let’s look more closely at the types of resistant starch you’re most likely to interact with:
RS2 is found in foods that contain uncooked or minimally processed starch, such as raw potatoes, underripe bananas, or certain strains of corn and wheat that have been bred to contain high levels of RS2.
Some of these are processed into specialty ingredients like green banana flour or high-amylose corn starch—also known as Hi-Maize. A special strain of wheat that is naturally high in RS2 is milled into a flour marketed as HealthSense. These ingredients are typically used in commercial food manufacturing, though a few are available for home use. For example, I purchased a resistant starch powder made from high-amylose corn, just to see what it was like.
It’s actually a little tricky to work with because it is such a fine powder that it’s a little hard to measure–and tends to make a mess. Another important feature of RS2 is that it is generally pretty heat sensitive; high or extended heat is likely to break the bonds that make it resistant to digestion, turning it into regular starch. But you could add it to smoothies or yogurt just to add a little extra fiber. One tablespoon of the stuff I bought, for example, contains about 5 grams of fiber but also 5 grams of regular starch.
Another consumer-facing product is the All-Purpose Baking Mix made by King Arthur flour, featuring that special strain of high RS wheat I mentioned earlier. This mix looks, performs, and tastes just like regular white flour but thanks to all that naturally occurring RS2 in the wheat, is significantly higher in fiber.
It can sometimes be hard to detect the presence of RS2 ingredients in commercial foods because while they may be identified as resistant starch or high-amylose flour, they could also be listed simply as cornstarch or wheat flour. The higher fiber content might be your only clue.
The third category of resistant starch (RS3) is technically described as retrograded starch. It is formed when certain starchy foods are cooked and then cooled. During the cooling, the starch molecules rearrange themselves into a shape that resists digestion.
You might remember this was a bit of a sensation a few years ago, when we all found out that you can increase the fiber (and decrease the carbohydrate and calorie content) of foods like potatoes, rice, or pasta, by allowing them to cool and eating them cold or gently reheated. This phenomenon is something that I talked about on this podcast way back in 2009, and then again in 2023.
Finally, let’s talk about RS4, which is not found naturally—it’s created through chemical modification that makes starch more resistant to enzymatic digestion. The main advantage of RS4 is that it is much more heat stable than RS2 or RS3, which makes it attractive to food manufacturers, who might use it in high-fiber breads, tortillas, snack bars, and baking mixes. It’s a little easier to spot RS4 in the ingredient lists because they are typically labeled as “resistant” or “modified” starch.
//
As I said earlier, all the different types of resistant starch are classified as dietary fiber–and that’s where they would be listed on the nutrition facts label. An interesting side note: Measuring the fiber contribution from resistant starch is trickier than with other fibers, because it requires simulating both the chemical and mechanical aspects of human digestion. And all of this has to be done on the final product (and not just the ingredients) because heat or other processing may change the molecular structures!
In any case, as we talked about in episode #560, dietary fiber can be sorted into different categories: soluble vs. insoluble, viscous vs. non viscous, fermentable vs. non-fermentable, etc. And these categories play a role in the specific health benefits, which you can learn more about in that episode.
So, where does resistant starch fit into that landscape? It is generally non-viscous (which is important in terms of food formulation), largely insoluble, and fermentable (which means that it provides a food source for your gut microbes). Moreover, resistant starch is also usually fermented more slowly in the gut, which may mean less gas or bloating.
But what do we know about the potential health benefits? Let’s start with the area where the evidence is strongest:
Because resistant starch isn’t digested and absorbed like regular starch, replacing digestible starch with resistant starch can lead to a smaller rise in blood sugar after a meal.
A meta-analysis of 13 clinical trials found that supplementing with resistant starch (10–45 grams per day) led to reductions in fasting blood glucose, fasting insulin, and HbA1c, particularly in overweight and obese adults, both with and without diabetes.
These effects may be due in part to increased production of short-chain fatty acids—especially butyrate—which help regulate blood sugar metabolism. There’s also some evidence that resistant starch may improve insulin sensitivity and satiety by promoting GLP-1 secretion.
Some research suggests that resistant starch may also help improve cholesterol levels.
In a meta-analysis of 20 controlled studies, resistant starch supplementation led to reductions in total cholesterol and LDL cholesterol, particularly when consumed at doses above 20 grams per day for more than four weeks. These improvements may result from RS binding to bile salts in the gut and increasing excretion.
Resistant starch acts as a prebiotic, serving as a food source for certain beneficial gut bacteria. Consumption of resistant starch has been shown to increase levels of acetate, propionate, and butyrate, which may help support gut barrier integrity, reduce inflammation, and modulate immune response. These effects can vary based on the source of RS and an individual’s baseline microbiome composition.
Resistant starch doesn’t seem to do much for promoting regularity. For that, you’d want to look for other types of fiber.
So, here’s the good news: Whether you are cooking with high-amylose flour, or cooling your rice and pasta, or buying products made with modified starch, introducing more resistant starch into your diet offers the same types of benefits as other prebiotic fiber. In that sense, it would appear to be just as legitimate a gut health strategy as eating more beans and legumes and other high fiber foods.
That said, variety is still the best strategy. Resistant starch shouldn’t replace other fiber-rich foods like beans, vegetables, fruits, and whole grains. However, it can be a great complement. Including resistant starch in your diet can be as simple as:
Thanks so much to Jerry for the great question that sparked today’s episode. And thanks as well to Katie Harris, a food scientist who works for Bay State Milling, the company behind the high-RS wheat flour used in HealthSense flour and who works with food service and food manufacturers to develop new products. Katie spent quite a bit of time with me helping me better understand the intricacies of resistant starch, so that I could share the best information with you.
If you have a question you’d like me to answer, you can email me at nutrition@quickanddirtytips.com.
I’d also love for you to check out my other podcast, The Change Academy, where we explore the art and science of creating positive behavior change in our lives, our workplaces, and our communities. Just search for Change Academy wherever you listen.
If you’d like to find out about having me speak at your next live or virtual event, you can learn more at wellnessworkshere.com
Nutrition Diva is a Quick and Dirty Tips podcast. Steve Riekeberg is our audio engineer, Holly Hutchings is our Director of Podcasts. Morgan Christianson heads up Podcast Operations & Advertising. Thanks also to Nat Hoopes for his support and most of all thanks to you for listening!