Resistant starch might explain the great health in traditional cultures where high-carbohydrate foods such as potatoes and rice are the staple. It feeds the gut probiotics, enabling them to produce nutrients, support immunity, and control inflammation. Learn the definition and types of resistant starch, food sources, and cooking tips to increase it in your diet.
There are two types of starch based on their branching chemical structures: amylose and amylopectin.
Starches are also categorized based on digestibility and glycemic index (the speed at which the starch increases blood sugar):
- Rapidly digestible starch – causes a sudden increase in blood glucose level after ingestion. Rapidly digestible starch is found in white bread and sugary breakfast cereals
- Slowly digestible starch – digests completely in the small intestine at a lower rate than rapidly digestible starch. Pasta, brown rice, barley, oatmeal, and whole wheat bread contain slowly digestible starch
- Resistant starch – does not absorb in the small intestine and is fermented in the large intestine
Resistant starches are the starches that are resistant to digestion in the small intestine. Therefore, they do not get absorbed in the small intestine but get fermented by the gut bacteria in the large intestine [1, 2, 3].
However, some whole food sources of resistant starch have a combination of resistant and non-resistant starches, so the actual glycemic index of these foods vary.
There are five different types of resistant starch, as categorized by their sources:
- RS Type 1 – Starch that is physically inaccessible to digestion because it is trapped in the fibrous cell walls of plants. It is found in coarsely-ground or whole cereal grains, seeds, and legumes (beans, nuts, peas, and lentils)
- RS Type 2 – Non-gelatinized starch with high amylose content. Amylose is a type of starch with a linear structure, which makes it more easily packed into a structure that prevents digestion. RS Type 2 is indigestible when raw. It is found in starchy fruits (green bananas), raw vegetables (potatoes), and high-amylose starches (maize starch)
- RS Type 3 – Retrograded starch that forms after type 1 or 2 are cooked and then cooled. Type 3 can be reheated at low temperatures to keep the starch from becoming digestible. RS Type 3 is found in bread, pasta, rice, and potatoes. Cooked potatoes and banana starches lose their resistance, but cooked high-amylose maize starch partially retains resistance to digestion 
- RS Type 4 – Starch that has been chemically modified (esterified starches) to resist digestion. RS Type 4 is a chemically modified starch found in processed foods like bread and crackers. Examples are hi-maize starch, cross-linked starches, starch esters and ethers, and cyclodextrins [9, 8, 5]
- RS Type 5 – Starch with amylopectin (a type of starch with non-linear, branching structure) that has been heated with oil and form a helical structure that makes it resistant to digestion 
All types of RS are beneficial for health, but they have different effects on your body .
When starch that is high in amylose is heated in water, the starch granules absorb water and swell up. After the cooked starch is cooled, the starch (amylose) molecules rearrange structures (crystalize) and become less digestible. This process is called retrogradation.
Cooked and cooled starchy foods with resistant starch may be reheated at low temperatures (below 175 °F) to maintain resistant starch content .
Baking does not degrade the starch as much as boiling does. Chilled potatoes (40 °F ) have more resistant starch than hot or reheated potatoes (150 °F). The chilled potatoes have retrograded starch, which is less digestible than cooked starch .
You can learn more about the “resistant starch diet” in this post.
Besides consuming starchy fruits, vegetables, and foods listed above, there are additional sources of pure resistant starch available.
Raw potato starch has by far the highest content of resistant starch and the lowest glycemic index. Corn has the next highest content of resistant starch, followed by tapioca, wheat, and rice .
Hi-maize is a high-amylose resistant starch that has been treated with heat and moisture to significantly increase its resistant starch content .
There is anecdotal evidence that some people are sensitive to plant-based starches, like the ones that come from a nightshade plant. For these people, Hi-maize is a good alternative. However, those with a corn allergy may want to avoid it.
Hi-maize has a uniquely high amount of resistant starch (50%) and dietary fiber. One serving (11 grams) contains up to 7 grams of dietary fiber. Unlike other natural sources of resistant starch, Hi-maize has a high gelatinization temperature that ensures its ability to survive and remain resistant through most normal food processing conditions [18, 19].
Hi-maize is used in a variety of processed foods, including low-fat snacks, high-fiber bread, noodles, pasta, breakfast cereal, and gluten-free products .