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Resistant starch RS3

Resistant starches

Retrograded starch: as it cools after cooking, it rearranges into crystals that digestion does not reopen.

It takes cold AND time: a night in the fridge for most of it, 24 h for the maximum — rice cooled for 24 h holds 2.5 times more than the same rice hot. Gentle reheating does not destroy it: what has retrograded stays retrograded.

Effects and benefits

Yesterday's rice beats today's. As cooked starch cools, it reorganizes into crystals that digestion can no longer open: it provides fewer calories, raises blood sugar more slowly and feeds a key bacterium of the colon, which then opens the meal to the others.

The phenomenon is called retrogradation. During cooking, starch unfolds and soaks up water; as it cools, its long amylose chains realign and fuse into crystalline zones that small-intestine enzymes can no longer attack.

A gram of starch that has turned resistant provides only about 2 kcal, against 4 for digested starch: it only returns its energy through the fatty acids that bacteria make. In one trial, rice cooked, cooled for 24 hours and then reheated raised blood sugar clearly less than the same freshly cooked rice (Sonia et al., 2015).

Replacing digestible starches with resistant starch in a meal contributes to a reduction in the blood glucose rise that follows (Regulation 432/2012).

Pasta, potatoes, legumes and grains cooked and then cooled all form it: yesterday's potato or lentil salad is a good example.

Ruminococcus bromii is the key species in breaking it down. Without it, much of the resistant starch crosses the colon unfermented: it is the textbook case of a bacterium that opens the door for the others.

Sources: Sonia et al., Asia Pac J Clin Nutr, 2015 · Ze et al., ISME J, 2012 · EU Regulation 432/2012 · EFSA, 2011

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Resistant starch