Resistant Starch and the Gut Microbiome: Effects on Gut Bacteria and Short-Chain Fatty Acids

Resistant starch is a type of starch that resists digestion in the small intestine and instead reaches the large intestine, where it can be fermented by gut bacteria. It has attracted growing interest for its potential effects on gut health, particularly its influence on the gut microbiome and the production of short-chain fatty acids (SCFAs). (1;2)

Resistant starch is found naturally in foods such as legumes, whole grains and green bananas, and can also form when certain starchy foods, such as potatoes, rice and pasta, are cooked and cooled.

One of the main reasons resistant starch has gained attention is its potential to influence the abundance of certain gut bacteria and the production of SCFAs. These compounds, including acetate, propionate and butyrate, are produced when gut bacteria ferment resistant starch and other carbohydrates that reach the large intestine. Butyrate is particularly important for gut health, as it provides an important source of energy for the cells lining the colon and helps support the intestinal barrier. SCFAs can also influence processes beyond the gut, including immune function. (3)

But does increasing resistant starch in our diet automatically lead to beneficial changes in the gut microbiome and greater SCFA production? The current research suggests that the answer is not so straightforward. Responses can vary depending on the type and amount of resistant starch consumed, as well as differences between individuals and their existing gut microbiome.

This article takes a closer look at human research investigating different forms of resistant starch and what the findings tell us about their effects on gut bacteria and short-chain fatty acid production.

What does the evidence say?

• A systematic review of 39 randomised controlled trials found that resistant starch supplementation was associated with increased faecal short-chain fatty acids in the majority of studies measuring them. However, results were not consistent across all trials. Most studies investigated Resistant Starch 2 (RS2) at doses of around 20–40 g/day, while relatively few investigated RS3. Considerable variation between individuals and differences in how SCFAs were measured limit the strength of the conclusions, particularly as faecal SCFA concentrations do not directly represent SCFA production or absorption in the colon. (1)

• A 2025 systematic review and meta-analysis of 24 randomised controlled trials involving 816 participants found that resistant starch increased several potentially beneficial gut bacteria, particularly Bifidobacterium and Faecalibacterium. However, responses varied considerably between studies and may depend on the type and source of resistant starch. These findings suggest that resistant starch can influence the gut microbiome, although the response may differ considerably between individuals. (2)

• In a randomised crossover trial, consuming one potato side dish per day for four weeks provided only around 1.7 g/day more resistant starch than refined-grain side dishes. This relatively small, real-world difference produced modest changes in the microbiome, including an increase in Roseburia faecis, but did not increase faecal butyrate or other SCFAs. The findings suggest that microbiome effects observed with high-dose resistant starch supplements should not automatically be expected from ordinary servings of starchy foods. (4)

• In a 2019 dietary intervention study, 174 healthy young adults consumed resistant starch from potato or maize, inulin, or a digestible starch control for two weeks.  Potato resistant starch increased total short-chain fatty acids by 32%, including a 29% increase in butyrate and a 21% increase in acetate. However, responses varied considerably: butyrate increased in 63% of participants but remained unchanged or decreased in 37%. Neither maize resistant starch nor inulin significantly increased butyrate. The increase in butyrate was associated particularly with increases in Ruminococcus bromii and the presence of the butyrate-producing bacterium Eubacterium rectale.  These findings suggest that the source of resistant starch and an individual’s existing gut microbiota can influence how strongly resistant starch increases butyrate production. (5)

• In a 2020 randomised controlled trial, 40 healthy adults consumed increasing doses of three different types of resistant starch (RS4) derived from maize, potato or tapioca for four weeks, reaching up to 50 g/day.  The effects differed considerably depending on the starch structure: maize RS4 increased the butyrate-producing bacterium Eubacterium rectale and increased butyrate, whereas tapioca RS4 increased Parabacteroides distasonis and propionate. Potato RS4 had little effect on the microbiota or short-chain fatty acids. Most effects increased with the dose and appeared to plateau at around 35g/day. These findings suggest that the type and structure of resistant starch may determine which gut bacteria are stimulated and which short-chain fatty acids are produced, rather than all resistant starches having the same effect. (6)

What does that mean in practice?

• Resistant starch can influence the gut microbiome, but more is not necessarily better. Different types of resistant starch appear to feed different bacteria and can lead to different amounts and types of short-chain fatty acids.

• Your individual gut microbiome matters. The same resistant starch can increase butyrate in some people but have little or no effect in others, depending partly on which bacteria are already present.

• Most of the stronger effects have been seen with supplements. Many studies used around 20–40 g of resistant starch per day, which is considerably more than the additional resistant starch you are likely to get from a normal portion of cooked and cooled potatoes, rice or pasta.

• Cooking and cooling starchy foods can still be a useful dietary habit, but it should not be viewed as a gut-health hack. The food-based potato study found modest changes in gut bacteria without an increase in short-chain fatty acids, so we cannot assume that cooling a portion of potatoes or rice will produce the same effects seen with high-dose resistant starch supplements.

Key takeaway

Resistant starch can influence gut bacteria and short-chain fatty acid production, but its effects depend on the type and amount consumed as well as the individual’s existing gut microbiome. While cooking and cooling starchy foods can increase their resistant starch content, current human evidence does not show that this produces the same microbiome effects seen with concentrated resistant starch supplements.

References:

1. Sobh M, Montroy J, Daham Z, Sibbald S, Lalu M, Stintzi A, et al. Tolerability and SCFA production after resistant starch supplementation in humans: a systematic review of randomized controlled studies. Am J Clin Nutr. 2022;115(3):608-18. doi:10.1093/ajcn/nqab402.

2. Xu J, Kong H, Li C, Ban X, Li Z. Effect of resistant starch supplementation on the diversity and composition of human gut microbiota: a systematic review and meta-analysis. Food Sci Hum Wellness. 2025;14(3):9250055. doi:10.26599/fshw.2024.9250055.

3. Chen Z, et al. Resistant starch and the gut microbiome: exploring beneficial interactions and dietary impacts. Food Chem X. 2024;22:101118. doi:10.1016/j.fochx.2024.101118.

4. DeMartino P, Johnston EA, Petersen KS, Kris-Etherton PM, Cockburn DW. Additional resistant starch from one potato side dish per day alters the gut microbiota but not fecal short-chain fatty acid concentrations. Nutrients. 2022;14(3):721. doi:10.3390/nu14030721.

5. Baxter NT, Schmidt AW, Venkataraman A, Kim KS, Waldron C, Schmidt TM. Dynamics of human gut microbiota and short-chain fatty acids in response to dietary interventions with three fermentable fibers. mBio. 2019;10(1):e02566-18. doi:10.1128/mBio.02566-18.

6. Deehan EC, Yang C, Perez-Muñoz ME, Nguyen NK, Cheng CC, Triador L, et al. Precision microbiome modulation with discrete dietary fiber structures directs short-chain fatty acid production. Cell Host Microbe. 2020;27(3):389-404.e6. doi:10.1016/j.chom.2020.01.006.

Disclaimer: This article is for educational purposes only and does not replace medical advice. Individual needs vary, and personalised guidance from a qualified healthcare professional is recommended for tailored support.