Gaby Sanchez CPD UT Austin with Kyndal Klose CPD UT Austin and Alexa Sparkman, MA, RDN, LD

Even though the American diet culture has vilified carbohydrates on and off for decades, some forms of carbohydrates, like resistant starch, provide such important health benefits not having then included in the diet could actually be harmful.

What is Resistant Starch?
Resistant starch (RS) is a form of starchy, fibrous carbohydrate that, as its name implies, is resistant to digestion. Normally, starches are digested and absorbed in the small intestine, however, by resisting digestion, resistant starch travels through the body until it reaches the large intestine. Once in the large intestine, resistant starch has the ability to be fermented by microbiota and essentially feed good bacteria found in the gut. Because of this, resistant starch has been found to function similarly to fiber and provides comparable health benefits. ^1-4

Classifications and Sources of Resistant Starch

Depending on structure or source, resistant starch can be categorized into one of the following classifications:

RS1 – Due to cell wall barriers, this type cannot be physically accessed by digestive enzymes.

Common sources include whole grains, seeds, and legumes.

RS2 – The crystalline structure of this type makes them indigestible.

Common sources include raw potatoes and under ripe bananas.

RS3 – This type, usually called “retrograde starch,” forms after it is exposed to cold temperatures after cooking.

Common sources include bread, tortillas, rice, pasta, and cooked and cooled potatoes.

RS4 – This type is resistant due to chemical modification of the starch.

This type can be found in a variety of products, but common sources are commercially prepared breads and cakes.

RS5 – This type involves two different components: amylose-lipid complexes, which form during processing and reform after cooking, and resistant maltodextrin, a process that intentionally rearranges starch molecules.
Types of Resistant Starch adapted from Health Effects of Resistant Starch²

It is important to note the amount of resistant starch in foods is not equal to the amount of carbohydrate listed on the nutrition label. Figure 1 compares grams of total carbohydrate in foods to grams of resistant starch in common starchy foods.

Figure 1: Grams of Carbohydrate and Resistant Starch in Common Food Sources

Chart adapted from Resistant Starch in Foods⁵

Health Benefits of Resistant Starch

Gut Health

As previously mentioned, when resistant starch reaches the large intestine, the bacteria in the gut ferments it. This fermentation process produces a few different types of short chain fatty acids that act as fuel to help control colonic blood flow.^1-3 Butyrate, for example, has been shown to induce apoptosis, also known as programmed cell death, which can decrease the risk of developing colon cancer. The short chain fatty acids produced in the gut were also found to help decrease the pH of feces, which can further decrease the risk of colon cancer. ²

Improved Glycemic Levels
Although continuing research is being done to further determine exact benefits, some research has shown increased consumption and supplementation of resistant starch can improve glycemic levels and insulin resistance in people with Type II diabetes; however, because research is so limited, using resistant starch as a sole method of improving glucose levels is not advised.^6-9

Body Weight Management

Dietary fiber has been shown to increase feelings of satiety and fullness which may help with weight loss. Although long-term research is lacking, resistant starches are also believed to have the same effects on satiety because of their similarity to dietary fibers. Increasing consumption of resistant starches can result in a lower caloric intake.¹

Although there is no official recommended daily intake of resistant starch, it was found that, on average, Americans consume 3 – 8 g of resistant starch per day. Because many different factors can determine the amount of resistant starch in an item, such as ripening, it can be difficult to accurately measure the amount consumed per day.^{2, 3, 8} If consuming more resistant starch is desired, it is recommended to consume a variety of starchy foods and/or include high amylose corn starch (contains 4.5 g of RS per 1 Tbsp serving) in cooking/baking.⁵  While high amylose cornstarch may be difficult to find in the grocery store, there is one product available online called Hi-maize. In addition to high amylose cornstarch, other resistant starch options for baking like teff flour or bean flour can be substituted for up to 25% of the normal wheat flour used in a recipe.

Green banana flour is another way to increase resistant starch intake. It has a mild banana taste when eaten raw. When cooked or baked, it loses all banana flavor and has a texture very similar to light wheat flour.  Preliminary research has shown that the type of resistant starch in banana flour is more resistant to heat than other sources like potato starch, which is encouraging for those of us who might prefer to cook with it than eat it raw. In addition, after the baked products cool, a portion of the resistant starch becomes active again.  Two tablespoons of green banana flour contains 13 gm carbohydrate about 50% will be resistant starch.  An additional 10-12 gm resistant starch per day over typical consumption may be associated with health improvements. This translates to adding one medium green banana to your morning smoothie; eating a medium baked potato with your lunch, and having ½ cup of lentils or white beans with your dinner.  Even more reason to include a variety of whole grains, minimally processed starchy vegetables and pulses in your diet.

References

1. Birt, D. F., Boylston, T., Hendrich, S., Jane, J., Hollis, J., Li, L., . . . Whitley, E. M. (2013, November). Resistant Starch: Promise for Improving Human Health. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3823506/
2. Lockyer, S., & Nugent, A. P. (2017, January 05). Health effects of resistant starch. Retrieved from https://onlinelibrary.wiley.com/doi/full/10.1111/nbu.12244
3. , & L., J. (2013, May 06). Carbohydrates, Dietary Fiber, and Resistant Starch in White Vegetables: Links to Health Outcomes | Advances in Nutrition | Oxford Academic. Retrieved from https://academic.oup.com/advances/article/4/3/351S/4644810
4. , C., K., L., C., F., Terry, E., K., . . . M., T. (2012, February 22). Resistant Starch from High-Amylose Maize Increases Insulin Sensitivity in Overweight and Obese Men | The Journal of Nutrition | Oxford Academic. Retrieved from https://academic.oup.com/jn/article/142/4/717/4630912
5. Resistant Starch in Foods for General Health | resistant starch. (n.d.). Retrieved from https://resistantstarchresearch.com/posts/rs-in-foods/
6. Higgins, J. A. (2004, May/June). Resistant starch: Metabolic effects and potential health benefits. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/15287677
7. Bindels, L. B., Walter, J., & Ramer-Tait, A. E. (2015, November). Resistant Starch for the management of metabolic diseases. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4612508/
8. Resistant Starch – This Type of Fiber Can Improve Weight Control and Insulin Sensitivity. (2012, September). Retrieved from http://www.todaysdietitian.com/newarchives/090112p22.shtml
9. Resistant Starch: The Carb With Health Benefits. (2018, July 26). Retrieved from http://n411.consultant360.com/n411/articles/resistant-starch-carb-health-benefits