Resistant Starch

What is resistant starch?

Resistant starch (RS) is a type of starch that is not broken down by human digestive enzymes, and it is therefore considered a dietary fiber. Starch occurs naturally in plants as a storage form of glucose. Upon consumption, some starch is quickly broken down into glucose molecules that can be absorbed into the bloodstream, but RS resists digestion and absorption in the small intestine and travels to the large intestine where it can act as a food source for microbes of the gut microbiota — particularly via bacterial fermentation. Bacterial fermentation of RS in the large intestine leads to the production of compounds capable of influencing human health — most notably short-chain fatty acids (SCFAs), like butyrate. While intriguing, the research on RS in humans has been mixed and inconsistent, and it’s not entirely clear how RS influences the gut microbiome or general health.

What are the different types of resistant starch?

There are various ways that starch can be resistant to digestion, which has led to the categorization of RS into five types (RS1–RS5), with RS2 being the most studied supplemental form. RS1: Starch that is protected within plant cell walls, such as in seeds, grains, or legumes.

What are resistant starch’s main benefits?

RS could have beneficial effects on gut health in several ways. Research suggests that RS supplementation may increase fecal weight and levels of butyrate, and reduce fecal pH — features that could potentially promote the health of the colon. However, these effects seem to vary depending on the type of RS used and on other factors that can influence the baseline microbiome. RS may stimulate the growth of potentially beneficial bacteria in the gut, but again, these effects tend to vary greatly and no consistent pattern has emerged. Beyond the gut, RS supplementation might reduce fasting blood glucose levels, improve insulin sensitivity, and reduce markers of inflammation. However, these effects are inconsistently found and tend to be small in magnitude, meaning they may not be particularly impactful.

Does resistant starch impact appetite or body weight?

SCFAs, including those increased by RS consumption, are thought to increase the levels of gut hormones involved in appetite regulation. Despite this, research examining the effect of RS on appetite, caloric intake, and weight status has mostly produced mixed or null results. A 2021 meta-analysis of randomized controlled trials found that in healthy young adults, RS caused short-term reductions in appetite, particularly at doses of at least 25 g daily. However, chronic supplementation has not been found to reduce appetite or caloric intake and there is little evidence to suggest RS reduces body weight.

Does resistant starch improve cholesterol levels?

Some types of fiber, like psyllium, beta-glucan, and other soluble fibers, can lower cholesterol levels. While RS can behave similarly to soluble fiber, most studies using RS have found little to no benefit on various measurements of cholesterol, including total cholesterol, triglycerides, LDL-C, or HDL-C.

Is resistant starch beneficial in chronic kidney disease?

Chronic kidney disease (CKD) is associated with alterations of the gut microbiome, sometimes referred to as dysbiosis. These changes may include reductions in the bacterial species involved in SCFA production and increases in bacterial enzymes involved in the production of uremic toxins. Because of this, RS has been a supplement of interest given its ability to modulate the microbiome and increase the production of SCFAs in some people. In a 2022 meta-analysis of randomized controlled trials, RS supplementation was found to reduce blood levels of indoxyl sulfate (a uremic toxin associated with worse health outcomes in CKD), phosphorus, interleukin-6, and uric acid in people with CKD undergoing dialysis. While this is promising, it is unclear whether these beneficial effects lead to any meaningful changes in health outcomes, and further research is required.

Does resistant starch reduce the risk of colorectal cancer?

Higher intakes of dietary fiber are associated with a reduced risk of colorectal cancer, but it is unclear whether RS has a similar effect. Some in vitro study and animal studies have suggested that RS could have a beneficial effect on colorectal cancer prevention, particularly related to butyrate production, but clinical trials to date have not found any beneficial effects. Interestingly, preliminary research suggests that RS supplementation might offset some of the potentially negative effects of red meat consumption on colorectal health.

What are resistant starch’s main drawbacks?

RS is generally considered safe and tends to be well-tolerated. Side effects are usually gastrointestinal in nature, including flatulence, bloating, diarrhea, and abdominal discomfort (particularly at higher doses of RS). These occur largely because of the gas produced during bacterial fermentation, and starting at a lower dose and increasing over time can help improve tolerance. One major limitation of RS is how variable its effect can be between individuals. Many of the potential benefits of RS are due to its interactions with the gut microbiome, but the microbes in the gut can vary greatly between different people, which could lead to inconsistent and unpredictable effects.

How does resistant starch work?

Most research suggests that RS works by acting as a source of fermentable fiber to feed microbes of the gut microbiome. When RS undergoes bacterial fermentation, it leads to the production of SCFAs like butyrate, propionate, and acetate. These SCFAs are capable of influencing the health of our body in a multitude of ways, including the promotion of a healthy gut environment and assistance with regulation of appetite, inflammation, and metabolism. The process of RS fermentation also encourages the growth of more bacteria capable of producing SCFAs, which might explain why the effects of RS tend to be more pronounced when taken for longer durations.