Starches are long chains of glucose that are found in wheat, potatoes, and other foods. But not all starches we eat are digested. In certain cases, a small part of these passes through the digestive tract, remaining intact. In other words, they resist digestion (resistant starch). This type of non-digestible starch is called resistant starch and acts a like a soluble fiber.
From a scientific point of view:
“Instead of being digested by the enzyme amylase in the upper part of the digestive tract, the resistant starch reaches the intestine where it is fermented and converted into short-chain fatty acids. These fats are acidifying and lower the pH of the intestine, facilitating the growth of good bacteria and inhibiting the growth of pathogenic bacteria. All this fermentation and the availability of fatty acids supplies energy to the enterocytes (the cell wall of the colon) that essence, represent a barrier against infection.”
Types of resistant starch (non-digestible)
There are four types of resistant starch.
1) One present in grain, seeds and legumes
2) That in starchy foods such as potatoes and raw green bananas
3) That forms when some starchy foods (such as potatoes and rice) are cooked and then cooled. The cooling converts part of the starch digested in a durable form through a process called retrogradation
4) That prepared by man-made chemical processes
How does resistant starch act on the bacterial flora of the intestine?
The main reason why resistant starch works is that it acts as a soluble fiber (fermentable). It passes through the stomach and small intestine undigested until it reaches the colon where it is absorbed by the good bacteria in the gut.
The bacteria in the gut exceeds the cells in a ratio of 1 to 10. While most of the foods we consume feeds only 10% of the cells, fermentable fiber and resistant starch feeds on the remaining 90% .
Resistant starch feeds the healthy bacterial flora with a positive effect on both the quality and quantity of bacteria .
When bacteria digest resistant starch, they form different compounds, including gas and short-chain fatty acids, in particular a fatty acid called butyrate.
The importance of butyric acid
In many animals, the highest concentration of butyrate is located in the gut. This is because it is produced by intestinal bacteria deriving from carbohydrates that can not be digested as cellulose and pectin.
It thus appears that butyrate was present in the intestines of mammals for so long that the wall of the intestine evolved in such a way that it can be used as a primary source of energy. Butyrate has many more functions to nourish the intestine. It’s anti-cancer and anti-inflammatory, so much so that researchers use supplements of butyrate and butyrate enemas to treat IBD conditions such as ulcerative colitis and Crohn’s disease. Some scholars argue that the problems affecting the bowel inflammation may be caused or exacerbated, in the first instance, by a lack of butyrate.
Butyrate and other short chain fatty acids produced by intestinal bacteria have an extraordinary effect on intestinal permeability. In experiments in vitro and in mice, the short chain fatty acids cause a rapid reduction in intestinal permeability. The loss of intestinal permeability is prevented by butyrate (or fiber) in mice with ulcerative colitis. This shows that butyrate and other short-chain fatty acids have their place in maintaining the integrity of the intestinal barrier.
The benefits of resistant starch
- Promotes the increased production of butyrate than other prebiotics and supports the proliferation of a healthy bacterial flora in the intestine
- Reduces the pH of the intestine and inflammation with benefits that help reduce the risk of colorectal cancer.
- Improves insulin sensitivity and postprandial glucose
- Improves appetite control
However, not all studies agree on the fact that the consumption of resistant starch ports all benefits.
Calories, carbohydrates, and fat resistant
Resistant starch is not digestible and therefore acts as a prebiotic fiber (food for the bacterial flora). The fermentation that occurs in the intestine produces butyric acid, a short chain fatty acid that is absorbed. And when it is absorbed (in the form of fatty acid), it contains 9 kcal per gram, like any other fat, and as 4 kcal per 1 gram of carbohydrates.To which, the fibers are not absorbed in the upper part of the digestive tract, but converted into fat and absorbed in the lower part, or in the colon.
Resistant starch content in foods
Before the advent of agriculture, our ancestors obtained resistant starch and other fermentable fibers from the consumption of various wild plants such as bulbs, tubers and herbs, foods that (besides not being very palatable nowadays) are not even readily available. According to some estimates, our ancestors ate up to 135 grams of fermentable fiber per day, resulting in beneficial bacterial flora. Today, for many reasons, consumption is decreased, and the depletion of the bacterial flora of the modern man is one of the most obvious consequences. In the era of microwaves, fast-food outlets, and globalized supermarkets, who would want to consume tubers, bulbs and roots raw, daily?
But we can somehow remedy this deficiency. A short list with some of the foods and those less rich in resistant starch:
- Raw potato starch : 9 grams per tablespoon (12 grams)
- Raw white potatoes : 25 grams per 100 grams
- White potatoes cooked : 2-5 grams per 100 grams
- White potatoes cooked and let cool for 24 hours: 5-10 grams per 100 grams
- Legumes (beans, lentils) cooked and left to cool: 5-10 grams 177-198 grams
- Cooked rice : 2-9 grams per 100 grams of rice
- Rice cooked and left to cool for 24 hours : 5-13 grams per 100 grams
- Plantain flour : 5 grams per tablespoon
- Dried plantain 50 grams of resistant starch per 100 grams
- Banana (unripe) : 10-20 grams (pint-sized, but can reach up to 34 gr.)
- Ripe banana : 0 grams
- Beet, Turnip, Carrot : 0 grams
- Jerusalem artichokes : 0 grams
- White flour : 0 grams
The amount of resistant starch in the food varies depending on whether raw, cooked, cooled, and according to the cooking method used. There is no single, official method to measure the amount of resistant starch in foods.
Sweet potatoes contain virtually resistant starch, except in very tiny amounts. The foods cooked and cooled for at least 24 hours may then be heated (temperature to no more than 60 ° C). Without that, the amount of resistant starch would be tainted. The raw and unmodified potato starch is composed of 78% resistant starch. One tablespoon (12 grams) of unmodified resistant starch contains 9 grams of resistant starch (not cooked).
The virtues of parboiled white rice
Parboilded rice has twice the amount of fiber than white rice cooked. Parboiled rice has a low glycemic index (38) than (89) of white rice. Once cooked, putting the rice in the fridge instead of letting it cool to room temperature produces a greater amount of resistant starch. On top of feeding the good bacteria in the intestine, resistant starch reduces the glycemic impact of slowing down the rate of digestion of sugars.