Resistant Starch
Also known as: RS2, RS3, Retrograded starch, Green banana flour
The fiber that survives digestion to feed gut bacteria — better blood sugar, stronger satiety, and butyrate for the colon.
In short
Resistant starch is a form of starch that resists digestion in the small intestine and reaches the colon intact, where gut bacteria ferment it into short-chain fatty acids — especially butyrate, the colon's preferred fuel. It occurs naturally in cooled cooked potatoes and rice (retrograded RS3), green bananas and raw oats (RS2), and legumes (RS1). Controlled trials show improved insulin sensitivity after meals, lower post-meal glucose spikes, increased satiety, and reduced calories absorbed (about 2 kcal/g instead of 4). It is one of the better-evidenced functional fibers, though starting doses cause gas and bloating in many people.
- Starch that resists digestion; fermented to butyrate in the colon
- Lowers post-meal glucose and improves insulin sensitivity
- Provides ~2 kcal/g versus 4 for regular starch
- Cold potatoes, rice, green bananas, and legumes are natural sources
What is Resistant Starch?
Resistant starch turns an everyday cooking habit — cooling your rice or potatoes — into a gut-health intervention. Because the starch retrogrades into a digestion-resistant form when cooled, it escapes to the colon, where bacteria convert it to butyrate and other short-chain fatty acids. The clinical payoff is well documented: smoother post-meal glucose, better next-meal insulin sensitivity (the 'second-meal effect'), and greater satiety. It also quietly cuts calories. The main adjustment is gastrointestinal — start low and build tolerance.
Where it comes from
Natural sources
- RS1: physically protected starch in whole grains and legumes
- RS2: granular starch in green bananas, raw potatoes, raw oats
- RS3: retrograded starch in cooked-and-cooled potatoes, rice, and pasta
How it's made
Supplements usually supply RS2 from high-amylose corn (Hi-Maize) or green banana flour.
What it does in products
Benefits
Blood sugar control
strong evidenceMeta-analyses of controlled trials find resistant starch reduces post-meal glucose and insulin, with the benefit extending to the next meal — the 'second-meal effect'.
Gut and colon health
moderate evidenceButyrate production supports colonocyte health and gut barrier integrity; resistant starch also increases stool bulk and butyrate-producing bacteria.
Satiety and weight management
moderate evidenceTrials report increased satiety hormones and reduced subsequent intake; longer-term weight-loss evidence is modest.
Side effects & safety
Safety considerations
- Safe as a food component in normal dietary amounts.
- May modestly reduce post-meal blood glucose — monitor if on insulin secretagogues.
- Not for: Severe small-intestinal bacterial overgrowth (SIBO) — fermentation can worsen symptoms
- Not for: Acute intestinal obstruction
How it's used
In supplements
10–30 g/day, starting at 5–10 g and titrating over weeks; some glycemic studies used 30 g.
In skincare
Not used topically.
Regulatory status
- Recognized dietary fiber by the FDA (2016 definition); supplements sold as fiber products.
- GRAS (generally recognized as safe) for food use.
- Not applicable.
Popular products containing Resistant Starch
- Bob's Red Mill Unmodified Potato Starch — Classic RS2 source used coldBob's Red Mill · Food
- Hi-Maize Resistant Starch — High-amylose corn RS2 powderIngredion · Supplement
- Anthony's Green Banana Flour — RS2-rich baking flourAnthony's · Food
Product names and brands are shown for reference and belong to their respective owners.
The second-meal effect
A landmark mechanism of resistant starch is improved glucose handling at the meal after the one containing it. Fermentation products reduce free fatty acid levels and improve hepatic insulin sensitivity overnight, so breakfast with resistant starch improves lunchtime glucose control. This makes it attractive for metabolic health beyond simple post-meal blunting.
How to get it from food
Cook rice, potatoes, or pasta, then chill overnight — retrogradation converts some starch to RS3, and reheating preserves much of it. Green (unripe) bananas, raw oats, and legumes contribute RS2 and RS1. Aiming for 15–30 g/day is achievable with a mix of cooled starches and legumes.
Frequently asked questions
Does reheating cooled rice destroy resistant starch?
Mostly not — retrograded starch survives gentle reheating. The resistant fraction formed during cooling largely persists.
How many calories does resistant starch have?
About 2 kcal/g versus 4 for digestible starch, because most of it is fermented rather than absorbed as glucose.
Can resistant starch help with weight loss?
It improves satiety and trims net calories, but trial evidence for meaningful long-term weight loss is modest — useful as an adjunct, not a standalone fix.
The bottom line
Resistant starch is a rare gut-health intervention with robust metabolic evidence: it feeds butyrate-producing bacteria, flattens glucose curves, and improves insulin sensitivity — with the familiar fiber caveat of an initial bloating phase.
References
- Health effects of resistant starch. Nutrition Bulletin. https://pubmed.ncbi.nlm.nih.gov/28607556/
- Resistant starch and postprandial glycemia: meta-analysis. PubMed. https://pubmed.ncbi.nlm.nih.gov/27409509/
- Resistant starch: a promising functional food ingredient. PubMed Central. https://pubmed.ncbi.nlm.nih.gov/33333871/