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Resistant starch

Starch that acts like fibre — fermented to butyrate, with promise for blood sugar and gut health.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden)Last reviewed July 2026Supplement guide

SupplementsFiberFermentable fibreButyrateBlood sugar

Resistant starch is starch that resists digestion in the small intestine and reaches the colon, where bacteria ferment it — producing a lot of butyrate, the gut lining’s preferred fuel.

Key takeaways

  • Fermented to butyrate — a short-chain fatty acid that nourishes the colon lining.
  • May improve insulin sensitivity and lower the post-meal blood-sugar response.1
  • Found in cooked-and-cooled potato/rice/pasta, green bananas, legumes and hi-maize supplements.
  • Introduce gradually — large amounts can cause gas.

What it is

Starch that isn’t absorbed as glucose but is fermented in the colon. There are four types (RS1–RS4): physically trapped, resistant granules (raw potato/green banana), retrograded (cooked then cooled), and chemically modified.

The evidence

Meta-analyses suggest resistant starch can modestly improve fasting glucose and insulin sensitivity and shifts fermentation toward butyrate.1 Effects on weight are small; gut-health signals are promising.

Dose

Benefits appear around 15–30 g/day. Cooling cooked starches (potatoes, rice, pasta) before eating raises their resistant-starch content for free.

Safety

Safe; increase slowly to limit gas. People with significant IBS may find high doses bloating.

Bottom line: a promising fermentable fibre — a butyrate factory for the colon with real (if modest) blood-sugar benefits; easy to get from cooked-and-cooled staples.

References

Adult research summary for education, not a prescription.

  1. Halajzadeh J, Milajerdi A, Reiner Ž, et al. Effects of resistant starch on glycemic control, serum lipoproteins and systemic inflammation in patients with metabolic syndrome and related disorders: a systematic review and meta-analysis of randomized controlled clinical trials. Crit Rev Food Sci Nutr, 2020;60(18):3172–84. pubmed.ncbi.nlm.nih.gov

This article summarises nutrition science for education. It is not a substitute for individual medical advice; consult a professional before starting a supplement, in pregnancy, or alongside medication.