Resistant starch
The fraction of starch that escapes digestion in the small intestine and reaches the colon intact, where it acts as a prebiotic fibre fermented by the microbiota.
Resistant starch (RS) « resists » digestive enzymes and behaves like fibre. On reaching the colon, it is fermented by bacteria into short-chain fatty acids, notably butyrate, with many benefits.
The 4 types of resistant starch:
- RS1: physically inaccessible (whole grains, seeds)
- RS2: resistant granules (green banana, raw potato)
- RS3: retrograded (formed by cooking + cooling: rice, pasta, cold potatoes)
- RS4: chemically modified (industrial)
An original angle (multiple benefits and ancestral diets):
- Blood glucose: slows glucose absorption and improves insulin sensitivity
- Microbiota: feeds the good bacteria and produces butyrate (anti-inflammatory, protects against colorectal cancer by lowering the pH of the colon)
- Satiety and weight: a study (Nature Metabolism, 2024) showed that resistant starch helps weight loss by remodelling the microbiota
- Digestion: beneficial in constipation, Crohn’s disease and colitis
Traditional diets around the world were naturally rich in RS (cooked-and-cooled starchy foods, pulses, plantains). Modern diets, low in RS (ultra-processed foods, starchy foods eaten hot), have lost this precious prebiotic source.
In practice: effects appear from about 8 weeks, with about 15 g/day. Introduce it gradually to avoid bloating. Sources: starchy foods cooked and cooled for 6 hours or more, green bananas, pulses, raw potato starch.