Character is eaten? Research finds that dietary fiber can change your mood

The so-called "people are what they eat" originally refers to what foods to eat can reflect a person's personality, or that people will like to eat different types of food under different mental states. A psychological study with reference to more than 500 case data found that the food a person likes to eat can reflect his/her personality and emotions, for example: people like to eat foods rich in sugar and caffeine when they are depressed ; And when in anger, they like to eat tough things, such as meat; those who are jealous will see whatever food is piled on the plate, which may indicate that they had opened up with their brothers and sisters at the table in childhood Fierce competition.

This study is the first close observation on the relationship between food and mental state, suggesting that diners may be able to change their diet to control their emotions.

In addition to temper and character, diet also affects a person's body shape and health. Extending the concept of "people are what they eat" means: what kind of food will be eaten, what kind of consequences will be brought to health. It can even be said that a person's physical condition is completely eaten out. In fact, it is true, many diseases and body types are eaten, especially obesity and its various complications.

For health, we should avoid improper diet, and prevent obesity and the diseases it brings from the source. In the daily diet, the health benefits of dietary fiber need to be paid more attention.

Benefits of dietary fiber

For a long time, as part of the diet, the potential health benefits of plant fiber have been appreciated. Epidemiological studies have shown that adding plant fiber to the diet can reduce the risk of heart disease, obesity and type 2 diabetes, and there is an inverse relationship between the two. Compared with animals that eat fiber-free food, animals that eat more plant fiber have lower fat content and are less likely to develop diabetes. However, what mechanism does plant fiber protect health through? Before, it was still unknown.

Two articles published in the journals "Nature" and "Cell" clarified the role of dietary fiber in dietary health. A team of scientists from France and Sweden successfully revealed the mechanism of action of plant fibers and made meaningful explorations to solve the mystery that plant fibers are beneficial to health.

Studies have found that the realization of this mechanism of action includes the intestinal flora and the ability of the intestine to produce glucose between two meals. Most fruits and vegetables are rich in fermentable fiber, which cannot be directly digested by the human body, but can be broken down by bacteria in the intestine into short-chain fatty acids, such as acetic acid, propionic acid or butyric acid, and these short-chain fatty acids can be absorbed by humans use.

Given that the potential health effects of dietary fiber have been widely known, and intestinal microbes are considered to be related to this because they contribute to the digestion of dietary fiber, therefore, the importance of intestinal microbes cannot be ignored.

The role of intestinal flora

The team of scientists led by Dr. Gilles Mithieux believes that the protective effect of dietary fiber is related to the ability of the intestine to produce sugar. Specifically, the intestine synthesizes glucose between two meals and releases it into the blood. The nerve endings of the portal vein can sense the glucose level and transmit signals to the brain. The brain triggers a series of protective signals.

The article shows that the intake of plant fiber may cause rapid conversion of the composition and function of the intestinal flora. Metabolites produced by microorganisms support metabolic health by regulating the control of glucose in the host. These results can guide our efforts to design "prebiotics" dietary supplements to manipulate the intestinal flora, thereby improving human health.

Soluble fibers, such as fructooligosaccharides and galactooligosaccharides, can be fermented by intestinal bacteria to produce short-chain fatty acids: acetic acid, propionic acid, and butyric acid.

Despite the similar chemical properties, the metabolism of these short-chain fatty acids is not the same, and their physiological effects on the host are also completely different. Among them, acetic acid is the most abundant short-chain fatty acid, which is a substrate for de novo synthesis of fat and biosynthesis of cholesterol by the liver; propionic acid is a substrate for liver gluconeogenesis; butyric acid is the energy substrate for intestinal cells in the colon. In addition, as signal transduction molecules, propionic acid and butyric acid can also bind and activate G protein-coupled receptors FFAR2 and FFAR3 (free fatty acid receptors, free fatty acid receptors).

Changing eating habits can change gut microbes

It is a recognized fact that changing dietary habits can change the composition of intestinal microbes. David et al. attempted to explore this phenomenon by measuring changes in the composition of intestinal microbes and gene expression profiles caused by changes in human dietary fiber intake.

To this end, they recruited 10 healthy human volunteers and divided them into two groups. One group was given a vegetarian diet and the other group was given meat food. They were observed for five consecutive days. During the study, at different time points, the volunteers’ stool samples were analyzed by sequencing 16S ribosomal RNA (to determine the relative abundance of different microorganisms) and RNA sequence (to determine the relative expression of microbial genes).

Within a few days of the start of the test diet, changes in microbial gene expression and community structure were seen. In the meat-eating group, these changes are related to a reversible physiological response (obesity), which is manifested as a large increase in bile-tolerant bacteria and fermented amino acids. On the contrary, the vegetarian group has higher plant polysaccharides derived from carbohydrate fermentation-fermenting bacteria and short-chain fatty acids. After the experimental diet was stopped, these parameters quickly returned to their original state.

This study confirmed that gut microbes can change rapidly according to dietary changes, and identified some molecular mechanisms, which may be the basis for healthy benefits from a plant-based diet.

The mechanism of action of dietary fiber and intestinal microbes

De Vadder et al. explored the many details of these mechanisms in detail, trying to understand exactly how short-chain fatty acids promote gluconeogenesis and thereby promote metabolic health. Different from liver gluconeogenesis, intestinal gluconeogenesis does not increase blood sugar under diabetic conditions; intestinal gluconeogenesis can activate portal glucose receptors, send signals to the brain, and produce beneficial effects on food digestion and glucose metabolism. Therefore, if dietary fiber and short-chain fatty acids can promote intestinal gluconeogenesis, it may be able to show that soluble fiber is good for metabolism.

Feeding rats oligofructose, propionic acid or butyric acid can improve glucose tolerance and enhance intestinal gluconeogenesis. However, propionic acid and butyric acid promote intestinal gluconeogenesis in different ways: propionic acid acts as a substrate or raw material for intestinal gluconeogenesis, and butyric acid acts as a signaling molecule to stimulate intestinal gluconeogenesis genes through cAMP signals. expression. In addition, propionic acid also directly activates the FFAR3 receptors in the peripheral nerves of the portal vein, and de-afferents from the portal area nerves, preventing propionic acid from intestinal gluconeogenesis stimulation, implying that the influence of propionic acid on intestinal gluconeogenesis involves intestinal-cranial nerve communication.

It is worth noting that feeding oligofructose or short-chain fatty acids can induce improvement in glucose tolerance, and it also requires gut-brain communication (determined by nerves in the portal area), and gluconeogenesis of the intestine (determined by the use of the small intestine of mice). G6Pase, that is, glucose-6-phosphatase catalyzes the decomposition of subunits).

David and De Vadder et al. used 16S ribosomal RNA sequences to track the changes in gut microbial composition. Among them, it is worth noting that unlike wild-type mice fed oligofructose, mice lacking G6Pase in the gut cannot be Benefit from fructose intake, although oligofructose caused very similar changes in the composition of the gut microbes of the two groups of mice. These results indicate that* the beneficial effects of diet on metabolic health may require not only a good composition of intestinal microbes, but also intestinal gluconeogenesis.*

Probiotics, prebiotics and post-prebiotics

A century ago, the Nobel Prize winner and Russian scientist Metchnikoff distinguished spoilage bacteria and sugar-decomposing bacteria from intestinal bacteria. The latter, especially the lactic acid bacteria, is good for health. His observation established the concept of using probiotics and prebiotics, which offset the adverse health effects of Western diets and lifestyles.

A large number of studies have pointed out that the use of probiotic supplements can stimulate specific intestinal bacteria to achieve established health goals. For example, ingesting starch products will escape digestion in the small intestine of healthy people. This is called "resistant starch", which can cause changes in the reproduction of intestinal microbes and transform them into more sugar-decomposing bacteria, similar to David The phenomenon observed by others in the plant-based diet.

Resistant starch feeding can also improve the insulin sensitivity of healthy adults, and oligofructose dietary supplements such as fructooligosaccharides and galactooligosaccharides can increase the proportion of bifidobacteria in human feces. Bifidobacterium has been proven to be beneficial to the health of young and old. Clinical trials have also shown that oligofructose and galactooligosaccharide can prevent atopic eczema in infants.

The research results of David and De Vadder et al. show that the probiotic method will provide a specific saccharification bacteria group that produces beneficial metabolites; the prebiotic method will supplement dietary fiber, which is conducive to the colonization and growth of intestinal bacteria. These two strategies are not mutually exclusive, but can be combined.

The third method is described in the research, by providing microbial metabolites directly as "postbiotics" to develop more dietary supplement strategies. The pharmaceutical industry may be interested in this approach, and the challenge will be to determine that synthetic FFAR3 agonists have improved pharmacodynamic characteristics that go beyond simple and cost-effective oral short-chain fatty acid supplementation.

The approach of probiotics, prebiotics and post-prebiotics is not as stark as they seem.

Here is a related case: In a mouse model of pathogenic E. coli infection, Bifidobacterium longum, as a probiotic, produces short-chain fatty acid acetic acid by transporting carbohydrates, which can strengthen the intestinal epithelial barrier function and therefore prevent fatalities. The Shiga toxin is transferred to the bloodstream, thereby protecting the host.

Questions about the transformation of new research still exist. For example, under different circumstances, the contribution of intestinal gluconeogenesis to human health is still uncertain. In any case, the work of David and De Vadder et al. provides a fascinating insight into the effects of dietary short-chain fatty acids on distant organs. Because acetic acid, propionic acid, butyric acid, and isovaleric acid are the most common metabolites in human feces—except for butyric acid, which is the most consumed by intestinal cells—also release into the bloodstream. Not surprisingly, short-chain dietary sources Fatty acids also have beneficial effects on tissues other than the intestine and brain.

A study conducted in a mouse model of allergic airway inflammation found that a high-fiber diet can reduce airway inflammation, while a low-fiber diet aggravated inflammation, which proves the existence of the intestine-lung axis. It is worth noting that the intake of propionic acid can reduce lung inflammation. In the case of FFAR3 dependence, it can reduce the ability of T lymphocytes from the lung draining lymph nodes to stimulate the dendritic cells in the precursor allergic phenotype. Although short-chain fatty acids have not been detected in the lungs, propionic acid can increase the production of dendritic cells in the bone marrow; in the lungs, the efficiency of allergic T cells before the activation of new dendritic cells is very low.

With its flexible metabolic capacity, the intestinal flora has become an important link between diet and host physiology. The research results of David and De Vadder et al. further explain this complex ecosystem and provide additional support for regulating the intestinal flora, which is an effective strategy to improve human health.