Resistant starch (RS) is a form of starch that cannot be digested in the small intestine. As a result it is classified as a type of fibre, providing approximately 2 kcal/gram. RS passes through the small intestine intact and is then fermented in the large intestine, producing short chain fatty acids (SCFA) which serve as an energy source for colonic cells. Foods that increase the amount of SCFAs in the colon are thought to be beneficial to health by helping to prevent the development of abnormal cells in the gut.
RS is naturally present in some foods such as bananas, potatoes, grains, pulses and seeds and is also produced or modified commercially and incorporated into some food products. The table below gives an indication of the RS content.
There are five different types of RS:
RS1 – inaccessible to digestive enzymes due to the physical barriers formed by cell walls and protein matrices. Present in bread, seeds and pulses.
RS2 – starches protected from digestion due to their crystalline structure. Present in potatoes (higher amounts in raw versus cooked), bananas (higher amounts in unripe fruits).
RS3 – retrograded starch formed when starchy foods (e.g. potatoes, pasta) are cooked then cooled.
RS4 – chemically modified starch formed by crosslinking, etherisation or esterification. Present in foods containing modified starches such as some bread and cakes.
RS5 – two different components have been proposed as RS5 either amylose–lipid complexes, which either form during processing or are created artificially; or resistant maltodextrin which is processed to purposefully rearrange starch molecules.
Resistant starch and gut health
RS has been noted to increase the production of SCFA in the gut and also to modulate the composition of gut microbiota, but there appears to be significant inter-individual variation in responses and health implications of these changes remain to be elucidated. There is some evidence that RS can counteract the detrimental effects of high red meat intake on colorectal cancer risk.
Resistant starch and glucose metabolism
There is good evidence that postprandial glycaemic responses to RS are reduced compared to digestible carbohydrates. As such, there is an approved health claim in the EU stating that baked products containing at least 14% RS in place of digestible starch reduce postprandial glycaemia. There may be synergism between RS and other fibre types in reducing glycaemic responses.
Resistant starch,appetite and body weight
There is some evidence that RS can decrease appetite and short-term food intake. Potential mechanisms include an increase in the release of gut hormones which promote feelings of satiety, stimulated by SCFA. However, as yet there is little evidence that RS can actually reduce body weight in humans.
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