Most of the carbohydrates in your diet are starches.
Starches are long chains of glucose that are found in grains, potatoes and various foods.
But not all of the starch you eat gets digested.
Sometimes a small part of it passes through your digestive tract unchanged.
In other words, it is resistant to digestion.
This type of starch is called resistant starch, which functions kind of like soluble fiber.
Many studies in humans show that resistant starch can have powerful health benefits.
This includes improved insulin sensitivity, lower blood sugar levels, reduced appetite and various benefits for digestion (1).
Resistant starch is a very popular topic these days. Many people have experimented with it and seen major improvements by adding it to their diet.
Not all resistant starches are the same. There are 4 different types (2).
- Type 1: Is found in grains, seeds and legumes and resists digestion because it’s bound within the fibrous cell walls.
- Type 2: Is found in some starchy foods, including raw potatoes and green (unripe) bananas.
- Type 3: Is formed when certain starchy foods, including potatoes and rice, are cooked and then cooled. The cooling turns some of the digestible starches into resistant starches via retrogradation (3).
- Type 4: Is man-made and formed via a chemical process.
However, this classification is not so simple, as several different types of resistant starch can co-exist in the same food.
Depending on how foods are prepared, the amount of resistant starch changes.
For example, allowing a banana to ripen (turn yellow) will degrade the resistant starches and turn them into regular starches.
Summary There are 4 different types of resistant starch. How foods are prepared has a major effect on the ultimate amount of resistant starch in food.
The main reason why resistant starch works, is that it functions like soluble, fermentable fiber.
It goes through your stomach and small intestine undigested, eventually reaching your colon where it feeds your friendly gut bacteria ().
Whereas most foods feed only 10% of your cells, fermentable fibers and resistant starches feed the other 90% (, ).
There are hundreds of different species of bacteria in your intestine. In the past few decades, scientists have discovered that the number and type of bacteria can have a profound impact on your health (, 9).
Resistant starch feeds the friendly bacteria in your intestine, having a positive effect on the type of bacteria as well as their number (10, ).
When the bacteria digest resistant starches, they form several compounds, including gases and short-chain fatty acids, most notably butyrate (, ).
Summary One of the main reasons why resistant starch improves health, is that it feeds the friendly bacteria in your intestine and increases the production of short-chain fatty acids like butyrate.
The most important of these short-chain fatty acids is butyrate (15).
Butyrate is the preferred fuel of the cells that line your colon ().
Therefore, resistant starch both feeds the friendly bacteria and indirectly feeds the cells in your colon by increasing the amount of butyrate.
Resistant starch has several beneficial effects on your colon.
It reduces the pH level, potently reduces inflammation and leads to several beneficial changes that should lower your risk of colorectal cancer, which is the fourth most common cause of cancer death worldwide (, ).
The short-chain fatty acids that aren't used by the cells in your colon travel to your bloodstream, liver and the rest of your body, where they may have various beneficial effects (, 20).
Due to its therapeutic effects on the colon, resistant starch may aid various digestive disorders. This includes inflammatory bowel diseases like ulcerative colitis and Crohn's disease, constipation, diverticulitis and diarrhea ().
In animal studies, resistant starch has also been shown to increase the absorption of minerals (, ).
However, the role of butyrate in health and disease needs to be studied properly in people before any strong recommendations can be made.
Summary By increasing the production of butyrate, resistant starch feeds the cells of your colon and leads to various improvements in the function of your digestive system.
Resistant starch has various benefits for metabolic health.
Resistant starch is also very effective at lowering blood sugar levels after meals (, ).
What’s more, it has a second meal effect, meaning that if you eat resistant starch with breakfast, it will also lower your blood sugar spike at lunch ().
The effect on glucose and insulin metabolism is very impressive. Some studies have found a 33–50% improvement in insulin sensitivity after four weeks of consuming 15–30 grams per day (, ).
The importance of insulin sensitivity cannot be stressed enough.
Having low insulin sensitivity (insulin resistance) is believed to be a major risk factor for several serious diseases, including metabolic syndrome, type 2 diabetes, obesity, heart disease and Alzheimer's.
By improving insulin sensitivity and lowering blood sugar, resistant starch may help you avoid chronic disease and improve your quality of life.
However, not all studies agree that resistant starch has these beneficial effects. It depends on the individual, the dose and the type of resistant starch.
Summary Many studies show that resistant starch improves insulin sensitivity and lowers blood sugar levels, especially after meals.
Resistant starch has fewer calories than regular starch — two vs four calories per gram.
The higher the resistant starches content in a food, the fewer calories it will have.
Several studies show that soluble fiber supplements can contribute to weight loss, primarily by increasing feelings of fullness and reducing appetite (, ).
Resistant starch appears to have has the same effect. Adding resistant starch to meals increases feelings of fullness and makes people eat fewer calories (, , ).
A few studies in animals show that resistant starch can cause weight loss, but this effect hasn't been studied properly in people.
Summary Resistant starch has fewer calories than regular starch and may increase feelings of fullness and help people eat less.
There are two ways to add resistant starches to your diet — either get them from foods or take a supplement.
Several commonly consumed foods are high in resistant starch.
This includes raw potatoes, cooked and then cooled potatoes, green bananas, various legumes, cashews and raw oats.
As you can see, these are all high-carb foods, making them out of the question if you’re currently on a very low-carb diet.
However, you can eat some if you're on a low-carb diet with carbs in the 50–150-gram range.
That being said, you can add resistant starch to your diet without adding any digestible carbohydrates. For this purpose, many people have recommended supplements, such as raw potato starch.
Raw potato starch contains about 8 grams of resistant starch per tablespoon and almost no usable carbohydrate.
What’s more, it's very cheap.
It tastes kind of bland and can be added to your diet in various ways, such as by sprinkling it on your food, mixing it in water or putting it in smoothies.
Four tablespoons of raw potato starch should provide 32 grams of resistant starch. It’s important to start slowly and work your way up, as too much too soon can cause flatulence and discomfort.
There's no point in taking much more than that since excess amounts seem to pass through your body when you reach 50–60 grams per day.
It may take 2–4 weeks for the production of short-chain fatty acids to increase and for you to notice all the benefits — so be patient.