Resistant starch

Carbohydrates are one of the three macronutrients, along with proteins and fats, that the body needs to function properly. One of the main functions of carbohydrates in the diet is to provide energy to the body. However, there are many diets that eliminate carbohydrates, such as the quite popular ketogenic diet, blaming them for weight gain, drowsiness or diabetes. However, not all carbohydrates can be lumped together. A notable exception is resistant starch, which is recommended for people with diabetes.

Not all starches are the same

As an introduction, I will explain that carbohydrates are divided into simple and complex, and complex carbohydrates into disaccharides (oligosaccharides) and polysaccharides (polysaccharides). Starch is a polysaccharide that can constitute up to 80% of carbohydrates consumed during the day. It is present in cereal grains, legumes and vegetables, mainly potatoes and other tubers and roots.

Starch consists of several hundred or even several thousand glucose molecules that combine with each other to form chains called amylose and amylopectin. Naturally occurring raw starch is for the human body indigestible, it requires culinary processing (cooking dumplings, potatoes, pudding), which will turn it into a form digestible for humans. Raw starch has a crystalline form, the particles adhere closely to each other and digestive enzymes have no way to access such starch. However, during cooking, starch absorbs water and swells, and the structures loosen and the starch takes a form that can be digested (so-called gelatinization). It is true that starchy products prepared in this way – e.g. potatoes, pasta or rice – exist easily digestible, but have a high glycemic indexwhich is why they are avoided by people suffering from diabetes and people on a low-carbohydrate diet.

Meanwhile, these products after cooking and cooling, they change their properties. Some of the starch they contain undergoes a retrogradation process when water is released and the starch molecules recombine into crystalline structures. This type of starch is called resistant starch proven positive effect on the human body. Interestingly, the discoverer of resistant starch was the Polish biochemist and food technologist Dr. Franciszek Nowotny.

Resistant starch is an important part of the diet.
Resistant starch is an important part of the diet.

Only benefits

Ordinary starch is absorbed in the small intestine, where it is broken down into simple sugars – maltose and glucose. Whereas resistant starch is not subject to the action of digestive enzymes and is therefore not converted into glucose. This means that the body does not have to secrete insulin, i.e. resistant starch has a positive effect on carbohydrate metabolism and at the same time prolongs the period of satiety.

Such undigested resistant starch in a virtually unchanged form it goes straight to the large intestine, which is inhabited by 1 to 2 kilograms of beneficial bacteria. The intestinal microbiome plays a key role in our body, and its incorrect composition is responsible for many diseases and illnesses. Resistant starch is an ideal medium for it. After entering the large intestine, intestinal bacteria convert it into short-chain fatty acids such as acetic, butyric and propionic acid. The increase in their concentration (compared to the content in a diet without resistant starch) contributes to a significant decrease in pH in the large intestine, thanks to which the development of pathogenic microorganisms is limited and the development of groups of bacteria beneficial to the body is stimulated.

Fatty acids also have a positive effect on the metabolism of lipids, especially cholesterol and triglycerides, and lead to a reduction in cholesterol levels in the blood and liver. However, butyric acid produced as a result of the fermentation of resistant starch plays an important role in preventing the formation of colorectal and rectal cancer. Eating meals rich in resistant starch also promotes better absorption of minerals such as magnesium, zinc, calcium, phosphorus, iron and copper in the large intestine. Short-chain fatty acids can also cause the release of appetite-reducing hormones (leptin, YY peptide, glucagon peptide), but this effect was observed in people who consumed resistant starch for at least a year – this was the time during which the intestinal microflora had the opportunity to adapt and regulate the hormonal system .

Resistant starch significantly reduces the concentration of urea in the blood. An adequate supply of resistant starch in the daily diet improves the functioning of the intestines, also affects their proper peristalsis and prevents constipation.

Types of resistant starch

So it turns out that asking about the carbohydrate content of a product is inappropriate because we should be asking about the resistant starch content. We can distinguish the following types:

RS1 (short for resistant starch) – starch physically inaccessible to digestive enzymes, found, for example, in incompletely ground cereal grains. It can be found in whole grain bread. It is not digested in the digestive tract and passes through the small intestine intact.

Stale grain bread is a good source of resistant starch
Stale grain bread is a good source of resistant starch

RS2 – is starch which, due to its high amylose content, cannot be digested in its raw state. Starch becomes available to digestive enzymes only after the product is cooked. Found in some plants, especially raw and unripe ones, such as raw potatoes or unripe bananas, and in legume seeds.

RS3 – is starch retrograde, i.e. one that changes its structure when the product is cooked and then cooled. It can be found in chilled potatoes, rice, pasta and cereals. An example of starch retrogradation is also the process of bread staling.

RS4 – is chemically or physically modified starch, obtained artificially and constituting an addition to highly processed products.

Retrograde resistant starch is of particular importance for the diet. After cooking and cooling of products containing starch (e.g. groats, pasta, dumplings, bread), changes occur in the starch molecule. Due to the fact that resistant starch is not digested completely, we get only 2 calories per 100 grams, even though it fills the stomach in the same way as regular starch, from the digestion of which we get 4 calories per 100 grams. Therefore, a portion of hot potatoes or rice is not identical in terms of nutrition and health to a portion of the same product eaten cold the next day. Cooked rice placed in the refrigerator overnight has up to 50% fewer calories than the original rice. The transformation of some starch into a resistant form not only reduces the caloric value, but also reduces the glycemic index of the dish.

Unripe bananas are a good source of resistant starch
Unripe bananas are a good source of resistant starch

Resistant starch should be consumed daily in amounts of at least 20g per day, but statistically speaking, most of us consume it four times less. About 2-8 grams of resistant starch is found in a medium-sized cooked and cooled potato (the GI of a cooked potato is 86, and the GI of a cooled-to-room-temperature potato is 54), 7-8 grams are found in half a cup of cooked, cooled white beans, and 3 grams – half a cup of cooked and cooled brown rice. Unripe bananas (12 g of resistant starch per 100 grams, while a ripe banana has only 4 g of resistant starch) and corn starch (resistant starch constitutes 50% of its composition) are also good products. In one publication for diabetics, I even found information that to provide yourself with resistant starch (RS3), you can drink potato flour mixed with lukewarm water (a tablespoon of flour per half a glass of water). It has been used for a long time natural way to deal with stomach problems.

As it turns out, blaming carbohydrates for all health problems is not entirely correct, and diets that completely or significantly eliminate the amount of carbohydrates in the meals we eat may deprive us of resistant starch, which is so valuable to our bodies. Instead of avoiding it, we should ensure the correct amount of it in our diet.

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