Carbohydrates are biomolecules composed of three atoms bound together: carbon, hydrogen, and oxygen. Of these biomolecules, starch is one of the most abundant in nature. Starch acts as the primary food reserve for plants, with grains and tubers representing the primary source of starch in food. Some starches are used to produce sugars for soft drinks and other processed foods. Other starches, particularly resistant starches, confer diverse health benefits that keep your gut microbes growing and your body healthy. In this article, we will answer the question, “what is resistant starch”; as well as how they work, metabolically, and their health benefits; the kinds of foods that contain them; and how you can integrate them into your diet.
What is starch?
Starch is a carbohydrate composed of glucose molecules linked together into chemical chains called polymers. Two types of glucose polymers can be found in starch, distinguished by where the chains are formed. Amylose has a straight polymer chain, while amylopectin has a polymer chain that forms branches. The ratio of amylose and amylopectin in starch determines whether the starch is one of these three types:
- Rapidly digestible starch is most commonly found in processed cereals and breads. The small intestine can digest most dietary starches with ease, being able to do so within 20 minutes. The ease of breaking down these starches means that rapidly digestible starches provide an immediate source of glucose for your body. This, in turn, causes your blood glucose levels to rise. Quick jumps in blood glucose levels increase the risk of insulin resistance and type 2 diabetes (T2D).
- Slowly digestible starches, such as those found in native waxy maize starch and legumes, take more time for the small intestine to digest, but get broken down after about 2 hours. Part of this delay relates to the fact that the enzymes in your saliva and stomach cannot break down these starches, so they provide a source of sustained glucose and help to stabilize blood glucose levels better than rapidly digestible starch.
- Resistant starch, most commonly found in legumes, has the highest concentration of amylose relative to amylopectin. With amylose being harder to digest than amylopectin, the small intestine is less able to digest resistant starch. On top of that, the mixture of amylose and amylopectin in these starches can make them particularly difficult to digest.
Benefits of resistant starch for your body
Because resistant starches face difficulties breaking down in the small intestine, they make their way into your large intestine. There, resistant starches provide a plethora of benefits for your gut health. Resistant starch benefits include:
- SCFA production: Resistant starches are an excellent fiber source, and they induce butyrate production by the gut microbiome. This process results in a wide range of benefits, including enhanced immune system function, improved large intestine integrity, and protection against gastrointestinal diseases.
- Non-alcoholic fatty liver disease (NAFLD): Resistant starches may also help reduce the risk of NAFLD through the gut-liver axis. The gut-liver axis represents a bi-directional relationship in which the large intestines supply nutrients to the liver and the liver supplies digestive enzymes to aid digestion in the small intestine. As stated before, eating resistant starches helps your gut microbes produce SCFAs. In doing so, the gut microbiome behaves in a way that enhances mucosal immunity and protects the large intestines from spilling toxins into the bloodstream and damaging the liver.
- Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) characterized by intestinal flammation and sores in the large intestine. A systematic review of 21 animal and 7 clinical studies showed that eating resistant starch reduced tissue damage in the large intestines of animals and improved IBD symptoms. The protection against UC afforded by resistant starch decreased tumor formation in the large intestines, reducing the risk of colorectal cancer.
A research/treatment caveat: Because resistant starches are compounds that help your gut microbes grow and keep your gastrointestinal tract (GI) healthy, they are considered prebiotics. However, resistant starches comprise a broad range of foods that, while all prebiotic, each exert a unique impact on your gut microbiome. Because all of us have unique microbiomes, future research must adopt personalized approaches to determine which sets of resistant starches will best promote healthy intestines in various individuals.
Despite the need for more research into resistant starches and how they could directly impact intestinal health, what we know already is that integrating resistant starches into your diet is associated with other health benefits, including:
- Glycemic control: Resistant starches may help control blood glucose levels better than other kinds of starches. A 2020 meta-analysis of 34 randomized control trials (RCTs) determined that eating resistant starch was associated with reduced blood sugar levels at fasting, although other insulin-related metrics did not improve. A subsequent 2022 pilot study showed that participants who ate a diet rich in resistant starch had reduced body mass index (BMI), fasting glucose, and insulin levels a week after starting the resistant starch diet.
- Reduced systemic inflammation: Low-level, yet persistent inflammation in the body is associated with aging and cardiovascular conditions. Eating resistant starches may help reduce the prevalence of low-level inflammation. A meta-analysis of 13 studies determined that eating resistant starches reduced the concentration of markers associated with increased inflammation, including interleukin (IL)-6.
- Obesity: Integrating resistant starches into your diet can also help prevent and alleviate obesity. Research in rat models suggests that resistant starch decreases abdominal fat. Eating resistant starch may also increase the production of hormones that signal feelings of fullness, reducing nutrient consumption. A diet rich in resistant starches also increases fat oxidation, lowering the amount of fat stored in the body.
Where to obtain resistant starch foods
The wide range of benefits that resistant starches can provide for the body makes them appealing to integrate into a healthy diet. With that in mind, here are some foods to add to your diet to get your fill of resistant starches:
- Oats are more resistant to digestion than other cereal starches because the amylose and amylopectin interact with lipids to form digestion-resistant complexes. After cooking the oats, consider cooling them for several hours or overnight, as this may increase the resistant starch content even more.
- Green bananas are also a rich source of resistant starch. As green bananas ripen to yellow bananas, much of the resistant starch is converted into simple sugars. (This is why green bananas taste bitter, while yellow bananas taste sweeter.) Green bananas are also rich in pectin, another excellent fiber that your gut microbes use to generate SCFAs.
- Potatoes: Raw potatoes and those that have been cooked and cooled also provide an excellent source of resistant starch. Baked potatoes also contain a higher resistant starch level than those that are boiled. Nevertheless, it would be prudent to consider other resistant starch options if you are seeking to adhere to a low-carb diet, as potatoes are very carbohydrate-rich.
- Legumes: Raw legumes have among the highest concentrations of resistant starch, comprising 20-30% of total weight. While cooked legumes still contain resistant starch, keeping the legumes uncooked maximizes the amount of resistant starch. Legumes are also a great source of protein if you’re interested in starting a plant-based or Mediterranean diet.
Resistant starch is an excellent prebiotic to integrate in your diet. Because the small intestine cannot break down these starches as easily, gut microbes in your large intestine can use them as an energy source. In doing so, they provide a wealth of health benefits for your GI tract and the rest of your body. Many of the foods we list in this report, which are also central to the plant-based and Mediterranean diets, provide excellent sources of resistant starches that you can eat alongside other types of fiber to enhance your body’s functioning and help prevent the development of various chronic disorders.