Healthy living & lifestyle
Research suggests resistant starch fuels beneficial gut bacteria, stabilises blood sugar and may aid weight loss.
also used as a fuel source by the cells lining your colon. Any SFA not used by the gut go into the bloodstream and circulate around the body.” Because of its poor digestibility, resistant starch is classed as a type of dietary fibre. It has things in common with its better-known counterparts, soluble and insoluble fibre – especially soluble fibre, which is also fermented in the colon. Not surprisingly, it shares many of the same health benefits, not least helping to balance out blood sugar, feeding the healthy gut bacteria and reducing constipation. From a chemical standpoint, though, there are differences. Soluble and insoluble fibre are composed from non-starch polysaccharides found in the cell walls of plants, whereas resistant starch is made up of starch molecules. In many ways, resistant starch, of which there are five different types, constitutes a category all its own. Like other forms of carbohydrate, the nutrient is found across a wide range of dietary sources. “These include nuts, seeds, wholegrains, unripe bananas, legumes such as peas and beans, and food high in carbohydrates that have been cooked and cooled,” explains Thornton-Wood. It’s the latter point that has piqued the attention of social media influencers, some of whom have filmed themselves freezing and thawing bread, or chilling and reheating baked potatoes. Bizarre though that might seem, starchy foods do change their chemical properties in response to cooking or cooling. When cooked, the starch granules lose their original structure via a process called gelatinisation. This changes the texture, makes the food easier to digest and increases its glycaemic index. (That’s useful from a taste perspective, but not so ideal for anyone watching their blood sugar levels.) Conversely, when that same food is cooled, the starchy paste reorganises itself into more orderly, crystalline structures, through a process called starch retrogradation. Resistant starch is created along the way, and much of this remains even when the food is reheated. In one 2015 study, white
rice that had been refrigerated and then reheated contained 2.5 times as much resistant starch as freshly cooked white rice. That’s a potential game-changer from a health perspective.
Separating fact from fiction So what are the key advantages of incorporating resistant starch into your diet, and how can we separate the reality from the hype? To start with a less controversial point, Thornton-Wood remarks that resistant starch is “definitely beneficial” to the gut microbiome. It is a type of prebiotic, meaning it fuels the healthy gut bacteria and helps their populations thrive. The SFAs produced along the way have anti- inflammatory properties. Prebiotics have been associated with benefits including better blood sugar control, a well-functioning immune system; improved absorption of calcium; and a lower risk of colorectal cancer. They may also stimulate the hormones that are responsible for controlling appetite. This could help people make better food choices and even facilitate weight loss. Last year, researchers in China conducted a small trial involving 37 participants. They found that, after receiving resistant starch supplements for eight weeks, people lost an average of 2.8kg (compared to no weight loss for people taking ordinary starch). On top of their weight loss, the resistant starch group experienced a smaller rise in blood sugar after meals. Their microbiome became more diverse, with several different bacterial species proliferating in their guts. These bacteria were also transferred to mice via faecal transplant. The mice in question lost some fat mass and improved their glucose tolerance.
Shedding weight
So if resistant starch does have an impact on body weight, what might the mechanism be? A 2022 review paper suggested a few possibilities. First, the SFAs produced during fermentation might impact our metabolism, increasing our total energy expenditure and rate of fat burn. Secondly, it may reduce our appetites through ‘the increased production of satiety signals’. Finally, since resistant starch is poorly digested, it reduces the calorific density of a meal. That cooled and reheated white rice would actually have fewer calories than the rice straight out of the pan. “There are only 2kcal per gram in resistant starch compared to 4kcal per gram for other forms of starch,” notes Thornton-Wood. “It has also been shown in some studies to increase feelings of fullness after eating, therefore resulting in a reduction in food intake.” Aside from the recent study in China, there have been plenty of small studies in animals and humans confirming these kinds of effects. However, there
54 Ingredients Insight /
www.ingredients-insight.com
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Shutterstock.com
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