What is Resistant Starch
Resistant starch (in English Resistant Starch - RS) constitutes 1/10 of food starch; it is a nutritional molecule that, for one reason or another, is NOT digestible by the salivary and pancreatic enzymes of the human being;
Types
The most popular types of resistant starch are 4:
- physically included resistant starch - RS1,
- native granular resistant starch - RS2,
- retrogradated resistant starch - RS3
- chemically transformed resistant starch - RS4.
Despite being different from each other, these 4 types of resistant starch are united by two chemical-physical characteristics, such as: linear structure of amylose and α-amylase resistance.
Let's look at them in more detail:
- Physically enclosed resistant starch - RS1: physically included resistant starch is a portion of amylose retained by the vegetable structures of the food; to be clearer, a typical example of foods containing physically included resistant starch is given by cereals, whole, cooked, NOT appropriately chewed. These, physically shielding themselves from amylases during digestion, reach the colon intact and ready for fermentation.
- Native granular resistant starch - RS2: native granular resistant starch is a compact and partially crystallized starch that, RAW, is immune to the aggression of α-amylases; on the other hand, when cooked, the native granular resistant starch undergoes GELATINIZATION and can be attacked by salivary and pancreatic enzymes in humans. This process is one of the reasons why both cereals and legumes need a heat treatment before they are digested.
- Retrogradated resistant starch - RS3: retrogradated resistant starch is the OPPOSITE product of native granular resistant starch; the RS3 is formed as a result of the excessive subjection to the heat of the starch which, after gelatinising, recedes to a form more similar to the initial granular one.
- Chemically transformed resistant starch - RS4: chemically transformed resistant starch is a type of starch that has interacted with other molecules or that has undergone profound chemical-structural alterations; they are chemically transformed resistant starches: esters, ethers and other starch complexes.
Dietary functions
Although not digestible, resistant starch interacts positively with the human organism because, by gelling together with the other components of the viscous fiber, it positively modulates the absorption of carbohydrates (lowering the glycemic index) and that of lipids (retaining some of them from the absorption, including cholesterol); moreover, the resistant starch and its anaerobic fermentation derivatives (short chain fatty acids: acetic acid, propionic acid and butyric acid) represent a valid growth substrate for the physiological bacteria of the intestinal flora, acquiring a remarkable PREbiotic function.
There is no need to remember that a good intestinal bacterial flora is essential to hygienic colon storage and many other functions.
Short chain fatty acids
As anticipated, the fermentation of resistant starch determines the release of short chain fatty acids; these are useful to the organism, even if in ways and places different from one another.
First of all, after absorption, acetic acid and propionic acid can be used for energy production; secondly, butyric acid (together with glutamine) constitutes an essential nutrient for the growth and trophism of the intestinal mucosa, in addition to (presumably) determining the apoptosis of tumor cells eventually present (effect demonstrated only in vitro).
