Resistant starch is a carbohydrate that is resistant to the action of digestive enzymes and in unchanged form passes into the large intestine. This is a medium for the development of beneficial intestinal bacteria and has many health-promoting functions.The benefits of consuming resistant starch are, among others, reducing the risk of developing cancer of the large intestine, lowering blood sugar and cholesterol levels and better absorption of minerals from food.
Starch, a carbohydrate composed of glucose monomers, has been considered a fully digestible food ingredient for many decades if it has undergone a thermal treatment It is now known that certain starch fractions called resistant starch pass through the digestive tract to the large intestine in an unaltered or almost intact state .
Resistant starch – what is it?
Resistant starch owes its name to the fact that it is not digested by enzymes of the gastrointestinal tract and is not absorbed in the small intestine.” It belongs to the components of dietary fiber The resistance of raw potato starch to the effects of amylolytic enzymes was first announced in 1937 by the Polish scientist Franciszek Nowotny. Again, the subject was returned 40 years later, when similar results were obtained by Japanese researchers.
There are four types of resistant starch (RS)
RS1 – physically unavailable starch contained in intact plant cells, eg whole grains, is undigested in the digestive tract, because it does not have enzymes that break down cell walls of plants. It passes through the small intestine intact.
RS2 – raw (non-backed) starch grains found in some plants, e.g. raw potatoes, immature bananas, legume seeds.
RS3 – grafted starch, which is produced in heat-treated food products, and then cooled.It is a starch, which at an elevated temperature has become gelatinized, i.e. it has become digestible for humans, and then precipitated in the retrogradation process.RS3 is in chilled potatoes, rice, pasta, cereals and stale bread.
RS4 – chemically or physically modified starch.
Starch resistant as fiber
In the classic approach, insoluble fiber is the components of plant cell walls that are not digested in the digestive tract, like cellulose, hemicellulose and lignin, and soluble fiber is pectin, gums and plant slimes.
Currently, the fiber components include resistant starch, because its consumption has the same health benefits for the human body as the consumption of other fiber components. Resistant starch has the effect of soluble fiber
Increases the volume of the digestive content, in the unchanged form passes through the small intestine, and when it goes to the large intestine, it is fermented by bacteria of the genus Bifidobacterium and Lactobacillus, or probiotic lactic bacteria that form the basis of a healthy intestinal microflora. Benefits of using resistant starch as prebiotic, or medium for the proper intestinal microbiome, is:
-fermentation of volatile compounds of methane and hydrogen and short-chain fatty acids, which leads to a lower pH level of the large intestine
-promoting the growth of beneficial bacteria, whose convenient environment is low acid pH and elimination of pathogenic bacteria that develop in neutral and alkaline environment
-production of short-chain fatty acids (acetic, propionic and butyric), which are used by intestinal cells as an energy and nutrient component and improve their functioning
-increased absorption of minerals, especially calcium and magnesium
-reducing the risk of colon cancer.
Products rich in resistant starch
Resistant starch as an ingredient beneficial to health should be consumed daily in an amount of at least 20 g per day.In developing countries, its average amount in the diet is 30-40 g, while in developed countries, including in the European Union countries, we consume an average of only 3-6 g of resistant starch per day.
To avoid unpleasant gastrointestinal complaints, such as bloating, gas and diarrhea, you should not eat more than 50-60 g of resistant starch per day.
The best sources of resistant starch are
beans – 8 g of resistant starch in 1/2 glass,
banana with green peel – 6 g of resistant starch in one large fruit,
wheat bran – 4.6 g of resistant starch in 1/2 glass,
cooked lentils – 3.4 g of resistant starch in 1/2 glass,
potatoes – 4 g of resistant starch in 1/2 glasses of chilled,
brown rice – 3 g of resistant starch in 1/2 glass of chilled,
maize – 2 g of resistant starch in 1/2 glass,
wholemeal bread – 1-2 g of resistant starch in 3 slices
Resistant starch – health properties
During the last decades of resistant starch and its potential health impact, a lot of attention has been devoted to it: resistant starch consumed in appropriate amounts contributes to the good health status of the large intestine, prevents intestinal inflammatory diseases and protects against colon and colon cancer – the fourth at the world causes deaths.
Resistant starch has less influence on lipid and glucose metabolism than non-starch polysaccharides, but nevertheless plays a significant role in lowering cholesterol and blood sugar levels.
The prebiotic and pro-health potential of resistant starch will probably be used in the large-scale food industry in order to introduce this valuable ingredient in a larger amount to the diet of the inhabitants of highly developed countries
Protection against colorectal cancer
There is scientific evidence that butyric acid, which is formed in the gut by the fermentation of resistant starch by bacteria, reduces the risk of cancerous changes in colon cells.
In a rat study, it was shown that the decrease in the pH value of the intestinal contents and the increased production of short-chain fatty acids were associated with a reduced incidence of colorectal cancer.
In vitro has demonstrated the special role of butyric acid and its salts in inhibiting malignant neoplastic colon cells.
In people who consumed less fiber, doubling this quantity resulted in a 40% reduction in the risk of colon cancer. The best effects of butyric acid secretion are achieved by combining insoluble fiber with resistant starch in the diet.
Resistant starch is metabolised only 5-7 hours after eating the meal as opposed to the glycated starches, the digestive process of which begins immediately after eating.
Effect on blood sugar levels
The presence of resistant starch in food products reduces their glycemic index and reduced insulin secretion after a meal. This is especially important for diabetics as well as for weight-controlling people because a small amount of insulin circulating in the blood promotes the use of adipose tissue as a source of energy.
Resistant starch is metabolised only 5-7 hours after food intake, unlike glued starch, which starts the digestion process immediately after eating, thus prolonging the hypoglycaemic effect of resistant starch and maintaining a feeling of fullness longer.
Food containing RS-3 lowers postprandial glycemia and may be of particular importance in controlling metabolism in type II diabetes. In order for resistant starch to show its beneficial effects on lowering blood sugar and insulin levels, it must account for at least 14% of the total starch in a meal.
Lowering blood cholesterol levels
The hypocholesterolemic effect of resistant starch is widely documented in animal studies, short-chain fatty acids resulting from the fermentation of resistant starch affects lipid metabolism.
In the case of experimental animals fed with starch resistant fodder, we found a reduction in total cholesterol, low and very low density lipoproteins (LDL and VLD), ie” bad “cholesterol, triglycerides, but also” good “HDL cholesterol.
Human studies have a beneficial or neutral effect on plasma lipoprotein levels. When consuming fasting starch, a reduction in total cholesterol and triglycerides or no change was noted in the study group.
The mechanism of action of starch resistant to fat metabolism in the human body requires a better understanding, but it is suggested that the reduction in blood cholesterol content due to the consumption of resistant starch is associated with a change in the composition of bile acids secreted into the large intestine
Lower risk of cholelithiasis and gout
A diet rich in easily digestible starch contributes to the formation of gallstones due to the increased secretion of insulin, while the introduction of a resistant starch in the diet reduces the risk of cholelithiasis
This conclusion was based on the analysis of the diet of the studied populations from highly developed and developing countries.
As a result of observing changes in the content of individual indicators in the blood after introducing resistant starch into the diet, it was noticed that its increased share in the diet results in a decrease in serum uric acid concentration and thus reduces the risk of gout.
Better absorption of minerals
Resistant starch increases the absorption of many minerals at the ileum level in rats and humans. In animals fed a diet rich in resistant starch, increased absorption of calcium, magnesium, zinc, iron and copper was noted.
In humans, resistant starch seems to have the greatest impact on calcium absorption. Comparing the absorption of calcium, phosphorus, iron and zinc in a meal containing only digestible starch and a meal with 16.4% resistant starch, the level of absorption of minerals was much higher in the second case.
Starch resistant – a role in slimming diets
Starch-rich carbohydrate products are the most caloric immediately after the heat treatment is finished, when the starch is largely clogged, and therefore the easiest to digest.
The colder the potatoes or pasta, the more starch is retrogradated, the proportion of resistant starch increases and the calorie content of the dish decreases.This phenomenon can be used in weight-loss diets and weight control.
To increase the amount of resistant starch in the diet, warm dishes rich in carbohydrates can be replaced with potato or pasta salads, as well as desserts, such as rice.
1. Voice of the University, Wrocław University of Environmental and Life Sciences, Lecture by Prof. Wacław Leszczyński
2. Fuentes-Zaragoza E. et al., Resistant starch as functional ingredient A review, Food Research International, 2010, 43, 931-942
3. Haralamp SG, Resistor starch – a review of the physical properties and biological impact of RS3, Carbohydrate Polymers, 2000, 41, 285-292