Dietary fiber makes the gut talk to the brain.

Does that sound weird? The explanation will come a little further down in the text.

You probably already knew that dietary fiber is carbohydrates from plants that cannot be digested by the small intestine. Instead, they continue into the large intestine, where they, in principle, work in two ways, both of which are important for our health. Either they also pass through the large intestine almost unchanged, acting as a bulk. These fibers, which are usually called non-fermentable, facilitate a smooth intestinal passage and bind toxic substances. The fermentable fibers, on the other hand, act as food for the bacteria in the large intestine. When fermented, they form many substances that are necessary for our metabolism. These include short-chain fatty acids that are needed, among other things, to keep the intestinal wall tight and prevent harmful substances from leaking into the blood. These substances are also part of a complex and relatively newly discovered signaling system between the large intestine and the brain. Hormones which, among other things, can tell the brain that we are full, are released from the intestinal wall. So: saying that the gut talks to the brain is quite correct.

The bacteria in the gut are usually called the gut flora. In a healthy adult, it consists of between four hundred and a thousand different bacterial species with a total weight of between one and two kilos. The gut flora is highly individual. It is founded early in life and is affected both by what we eat and by environmental factors. Different types of dietary fiber stimulate the gut flora in different ways. It is good to eat many different varieties, from, for example, whole grains, legumes, and vegetables.

The fermentable dietary fiber helps to lower cholesterol levels in the blood. Many dietary fibers also have a blood sugar regulating function that can last for a long time. For example, legumes, in combination with rye and barley, have been shown to give a slow and controlled rise in blood sugar that can provide something called a “second meal effect.” A prolonged feeling of satiety which means that you eat less of a subsequent meal. My research colleagues at the Antidiabetic Food Center (AFC) were able to show that the effect lasted for up to 14 hours after a meal. This should be good news for anyone trying to reduce or maintain weight. Such a blood sugar curve can also have other effects and even make our brains work better. One of my colleagues at the AFC set up a breakfast study with two groups of subjects. While one group was given a plain white bread, which gives a rapid and steep rise in blood sugar, the other group was given a white bread containing a fermentable dietary fiber, which allows the carbohydrates to be absorbed slowly. A couple of hours after breakfast, the groups’ so-called cognitive ability was measured in different ways, and those who ate the “slow” bread performed best. Even if that particular bread is not available for purchase in the store yet, the study’s result gives a hint about what kind of breakfast is right to eat for the brain to function optimally.

And of course, it’s a little fun to think that it’s the slow fibers that make the brain fast.

Some links to research articles that might be of interest:

Dietary fiber effect on cholesterol levels

Importance of diet for gut flora composition

Dietary fiber effect on cognition

Second meal-effect from barley and legumes

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