Resistant starch is starch that escapes digestion in the small intestine, for example because it is protected by intact plant cell walls (type 1), is high in amylose (type 2), has cooled and recrystallized (type 3), or has been chemically modified (type 4). It is studied mainly for blood sugar control.
Also known as: RS, RS2, high-amylose maize starch, potato starch.
A 2019 meta-analysis included trials of at least 8 g of type 2 resistant starch a day (Snelson 2019); a 2021 meta-analysis found larger effects on fasting blood sugar above 28 g a day (Xiong 2021). These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling.
What studies show: compared with digestible starch, a 2021 meta-analysis of 19 trials found resistant starch lowered fasting blood sugar slightly (0.09 mmol/L) and improved insulin resistance (HOMA-IR), but not other insulin measures (Xiong 2021). A 2019 meta-analysis of 22 short trials (670 people, 1 to 12 weeks) of type 2 resistant starch found lower triglycerides in healthy people and 1.29 kg less weight in people with type 2 diabetes, but these results rested on a few studies, nothing else changed, and the authors concluded short-term use is of limited cardiometabolic benefit (Snelson 2019). In people with type 2 diabetes or prediabetes, types 1 and 2 lowered blood sugar after meals (Pugh 2023).
Safety: the sources here do not describe side effects or drug interactions.
Resistant starch is not digested in the small intestine (Pugh 2023), so a half-life or time to peak does not apply.
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