Book summary “Gut”: summary

Introduction

You likely experience bowel habits as an embarrassing topic or a simple tube of waste management. Modern life often leaves you bloated, stressed, or confused by conflicting diet advice while ignoring your body's most sophisticated organ.

The gut is an astonishingly sophisticated organ that shapes our physical health, mental well-being, and daily emotional life.

Giulia Enders reveals that your digestive tract runs the show from brain chemistry to immune defense. You will explore the journey of food from mouth to exit while discovering how tiny organisms dictate your daily vitality.

• How does your digestive nervous system operate without brain input?
• Which microbes live inside you and protect your health?
• What causes your gut feelings and emotional states?

1. Gut Feeling and Anatomy

The human body develops essentially from three separate tubes: the cardiovascular system, the nervous system, and the intestinal tube. The intestinal tube runs from end to end through the body and gives rise to internal furnishings such as lungs, liver, gall bladder, pancreas, mouth, esophagus, and stomach before forming the gut.

The intestinal tube forms the core of human embryonic development, while the mouth, esophagus, and stomach feature sophisticated anatomical structures to process food and protect health.

Salivary glands filter blood to produce up to two pints of saliva daily, which hardens teeth but can also cause tartar. Saliva contains calcium to make teeth harder, but constant exposure can fossilize floating molecules into rough tartar. This rough surface helps harmful bacteria cling to teeth, making regular brushing essential.

Saliva uses mucin proteins to form protective microscopic nets that trap bacteria in the mouth. Salivary papillae shoot mucin nets to catch harmful germs. During sleep, saliva production drops significantly, allowing unhindered bacterial activity that causes morning bad breath.

• Brush your teeth before you go to bed at night to reduce bacteria
• Brush your teeth after you get up in the morning to clean up nocturnal microbes
• Use a tongue scraper to remove musty-smelling bacteria
• Chew gum to stimulate saliva production and clear mucin hideouts

Saliva contains a natural painkiller called opiorphin that is stronger than morphine and helps soothe oral sores. Discovered in 2006, opiorphin is produced in small amounts and acts as an oral anodyne, reducing pain sensitivity in the mouth and potentially possessing antidepressant properties. Waldeyer's ring of immune tissue in the throat, including the tonsils and lingual tonsils, trains the immune system until age seven. Tonsils investigate swallowed or inhaled foreign particles to train immune cells. Removing tonsils in children under seven can disrupt immune development and lead to an increased risk of obesity.

Icelandic and American researchers in 2012 split twenty-nine psoriasis patients into two groups, discovering that thirteen out of fifteen patients who had their tonsils surgically removed reported significant long-term skin improvement.

Structure of the Gut

The esophagus connects to the stomach at a side angle rather than the top to protect against abdominal pressure. Surgeons call this terminolateral connection a smart move because walking, laughing, or coughing doubles or multiplies abdominal pressure. Docking at the side means the esophagus deals with only a fraction of this pressure, preventing constant burping after a heavy meal.

The lopsided stomach separates fluids from solids, and excess gas in the stomach can trigger serious symptoms known as Roemheld syndrome. The stomach's misshapen Quasimodo structure allows water to flow straight down the shorter right-hand side toward the small intestine, while solid food plops against the larger side. Excessive gas buildup can press against the heart and nerves, causing dizziness, anxiety, or chest pain mimicking a heart attack.

Microscopic folds, villi, and microvilli in the small intestine create a massive surface area equivalent to about 4.5 miles in length. The gut enlarges its surface area to break down external substances until they are tiny enough for the body to absorb. Each square inch contains about 20,000 villi, covered in microvilli, which are further covered in sugary glycocalyxes, resulting in a total digestive surface area one hundred times greater than the skin.

Dietary fat bypasses the liver initially and enters the bloodstream directly via the lymphatic system to prevent capillary clogging. Because fat is insoluble in water, absorbing it directly into blood capillaries would clog them. Instead, fat is absorbed via thin lymphatic vessels that converge into the thoracic duct, which empties directly into the heart, bypassing the detoxifying liver until later in circulation.

The vermiform appendix acts as a storehouse for helpful bacteria and an immune checkpoint after bouts of diarrhea. Positioned just below the junction of the small and large intestines, the appendix is made almost entirely of immune tissue to monitor microbes. Researchers Randal Bollinger and William Parker discovered in 2007 that a healthy appendix acts as a storehouse of helpful bacteria to repopulate the large intestine after diarrhea flushes the terrain.

The large intestine doggedly processes leftovers for hours, absorbing crucial minerals, vitamins, and fluids before excretion. Taking around sixteen hours to process leftovers, the large intestine absorbs important minerals like calcium, energy-rich fatty acids, vitamin K, vitamin B12, thiamine, and riboflavin. It also fine-tunes water and salt levels, saving the body an entire quart of fluids daily.

Gluten can make the gut wall porous, triggering immune responses ranging from celiac disease to milder gluten sensitivity. Wheat plants produce gluten as a mild deterrent against insects. In humans, gluten can pass into gut cells in a partially undigested state, slackening cell connections and alarming the immune system. Celiac disease damages villi and requires a strict gluten-free diet, whereas gluten sensitivity causes milder symptoms without intestinal damage.

Lactose intolerance is a normal enzyme deficiency, while fructose malabsorption occurs when gut transporters are overwhelmed. In 75 percent of the world's population, the gene for digesting lactose switches off after weaning, sending undigested lactose to feed gas-producing microbes in the large intestine. Similarly, excessive fructose overtaxes GLUT5 transporters or unabsorbed fructose binds to tryptophan, potentially impacting serotonin production and mood.

Defecation is managed by a sophisticated team of two sphincters representing different nervous systems. The outer sphincter is consciously controlled, while the internal sphincter is unconscious and focuses on inner comfort. Before deciding to go, the internal sphincter lets a small taster through to sensor cells between the muscles to analyze whether the product is solid or gaseous.

Squatting is the anatomically natural position for defecation and prevents excessive strain on the gut. When sitting or standing, a lasso-like muscle creates a kink in the rectal tube as an extra closure mechanism, forcing feces to brake around a corner. Squatting relaxes this muscle, straightens the tract, and reduces the risk of hemorrhoids and diverticular disease.

Israeli doctor Dov Sikirov asked twenty-eight test subjects to use three different toilet positions, finding that squatting took an average of 50 seconds with complete emptying, compared to 130 seconds while seated.

• Incline your upper body forward slightly
• Put your feet on a low footrest placed in front of the toilet

The Bristol stool scale classifies fecal consistency into seven groups, with types 3 and 4 representing optimal digestive health. Developed by Dr. Ken Heaton at the University of Bristol in 1997, the scale ranges from hard separate nuts taking 100 hours to pass (Type 1) to entirely liquid stools passing in 10 hours (Type 7). Type 4 represents the ideal balance of fluid and solid content, resembling a smooth, soft sausage or toothpaste.

• Type 1: Separate hard lumps, like nuts (hard to pass)
• Type 2: Sausage-shaped, but lumpy
• Type 3: Like a sausage but with cracks on its surface
• Type 4: Like a sausage or snake, smooth and soft
• Type 5: Soft blobs with clear-cut edges (passed easily)
• Type 6: Fluffy pieces with ragged edges, a mushy stool
• Type 7: Watery, no solid pieces, entirely liquid

2. The Nervous System of the Gut

The enteric nervous system operates the digestive tract with complete autonomy, coordinating transport, swallowing, and emergency defense programs like vomiting.

The gut is cosseted by three coats of smooth muscle tissue directed by the enteric nervous system. If the connection to the brain is severed, the digestive tract continues operating as if nothing happened, a unique property not found in any other organ system.

Transport and Swallowing

Jaws can exert pressure of up to 180 pounds or 80 kilos on each molar, equivalent to the weight of a grown man. Tooth enamel is the hardest substance produced by the human body.

Adults swallow between 600 and 2,000 times a day, involving more than 20 pairs of muscles. In old age, coordinating muscles may work less precisely, increasing the risk of choking.

• Seek out a speech therapist to help whip your swallowing squad into good shape before choking attacks become too frequent.

The stomach swings food to and fro and lobs it against the stomach wall in a process called retropulsion. The stomach can stretch to accommodate two pounds or one kilo of food. Simple carbohydrates pass through quickly and spike blood sugar, while proteins and fats like steak are detained for hours. The stomach exit allows particles through only if they measure no more than 2 millimeters or one-twelfth of an inch, meaning a piece of steak may be churned for 6 hours.

An internal cleaning mechanism called the migrating motor complex sweeps leftover debris through the gut between meals. Nicknamed the little housekeeper, this complex begins an hour after digestion finishes, creating the rumbling belly sound. Constant snacking interrupts this cleaning process.

• Leave five hours between meals to allow the housekeeper time to clean.

The total transit time from fork to toilet averages one day, ranging from 8 hours for fast guts to 3.5 days for slow digesters. Cake particles may linger in the large intestine for 12 to 42 hours. A Dutch study indicated that once-a-day or less frequency is associated with lower risks of certain rectal diseases, while a healthy frequency reaches 2 to 3 times a day if sufficient bulk is provided.

Reflux, Vomiting, and Constipation

About a quarter of Europeans regularly experience reflux. Factors like cigarette smoke, pregnancy hormones, and certain foods relax the lower esophageal sphincter. Proton pump inhibitors and antacids provide short-term relief, but reliance on them for 4 weeks or more becomes a warning sign.

• Chew gum or sip tea to help nudge the nerves in the right direction downward.
• Use relaxation techniques to reduce hectic nerve instructions.
• Prop the upper body up to an angle of 30 degrees if attacks strike at night.

Vomiting is an orchestrated emergency defense program coordinated by the brain and gastrointestinal tract to expel toxins or save energy under stress. The body triggers excessive salivation to protect teeth from gastric acid, drains blood from the face, and uses abdominal muscles and the diaphragm to expel contents. Certain animals like rats and horses cannot vomit.

Forty studies validate the effectiveness of the P6 acupuncture point against nausea.

• Keep your eyes fixed on the horizon far ahead to reduce travel sickness.
• Listen to music on headphones, lie on your side, or try relaxation techniques.
• Consume genuine ginger to block the vomit center of the brain.
• Use pharmacy-bought drugs or antihistamine-like medications that suppress histamine.
• Gently stroke or apply pressure to the P6 acupuncture point located two to three finger-breadths below the wrist between the two prominent tendons.

Between 10 and 20 percent of people in the United States are constipated. Temporary travel constipation stems from schedule changes, dehydration, and unfamiliar toilets.

• Consume dietary fiber such as psyllium seed husks and plums alongside sufficient fluids, aiming for an appropriate daily dose of 30 grams or one ounce.
• Do not suppress the urge to go to the toilet.
• Try the rocking squat technique by bending your upper body forward toward your thighs and straightening up on the toilet.
• Use osmotic laxatives, fecal lubricants, or hydragogues as targeted box-of-tricks options, keeping in mind it can take three days for the large intestine to fill up again after a strong laxative.

3. The World of Microbes

Trillions of microorganisms inhabit the gastrointestinal tract, forming a complex ecosystem that trains our immune system and shapes metabolism.

The vast majority of the human microbiome resides inside the gut, where it aids digestion, manufactures vitamins, and influences metabolism. In 2007, work began on an atlas of human bacteria to map this internal community. Comprising 100 trillion bacteria across more than 1,000 different species, the gut microbiome acts as an internal ecosystem that breaks down otherwise indigestible foodstuffs.

99 percent of the body's microbiome is found in the gut. Up to 4½ pounds or 2 kilos represents the maximum weight of the gut's microbiome. 1/32 of an ounce or 1 gram of feces contains more bacteria than there are people on Earth. Less than 1 percent of the gut population is made up of E. coli. Skewed proportions within this bacterial community have been linked to obesity, malnutrition, and chronic digestive disorders.

Researchers checking belly button flora in 2011 found a volunteer's navel contained bacteria previously known only in Japanese coastal waters.

I Am an Ecosystem

The human gut hosts representatives of three major living categories: eukaryotes, archaea, and bacteria. Eukaryotes feature large, complex cells including yeasts. Archaea are intermediate organisms often known for thriving in extreme environments like extreme heat or acid. Bacteria make up over 90 percent of the gut population and are categorized into lineages and families.

Biologists divide bacteria into over twenty phyla. Extremophiles tolerate conditions ranging from 212 degrees Fahrenheit for hyperthermophiles to minus 112 degrees Fahrenheit for cryophiles in laboratory freezers. Other groups include acidophiles, barophiles, and halophiles.

Gut bacteria possess a massive collective genetic library, called a biome, that significantly expands our metabolic capabilities beyond our human DNA. Taken together, gut bacteria have 150 times more genes than a human being. These genes act as operational plans that can influence your body's abilities, such as how you digest specific foods or process medications like acetaminophen.

Babies possess more active genes for digesting breast milk, obese people have more genes for breaking down carbohydrates, and older people have fewer genes for dealing with stress.

Human gut microbiomes organize into three distinct enterotypes dominated by specific bacterial families regardless of age or gender. Researchers in Heidelberg discovered in 2011 that one of three bacterial families always dominates the gut ecosystem: Bacteroides, Prevotella, or Ruminococcus. These enterotypes dictate how you process food, detoxify substances, and interact with other bacteria.

The Bacteroides enterotype excels at carbohydrate extraction and functions as a biological factory for vitamin B7. Bacteroides possess vast genetic blueprints to manufacture enzymes needed to extract energy from almost any ingested food. They also produce biotin, which neutralizes the toxic effects of avidin and supports vital metabolic processes.

Genetic engineers created transgenic corn producing avidin to poison insect pests, which poses a future risk of biotin deficiency for grazing pigs.

The Prevotella enterotype is frequently found in vegetarians and produces sulfur compounds along with thiamine. Prevotella bacteria work alongside flagellated Desulfovibrionales to scour mucus membranes for proteins, releasing sulfur compounds. They also produce thiamine, preventing deficiency conditions like beriberi.

Polishing rice removes the thiamine it contains, and a diet consisting predominantly of polished rice historically led to beriberi, first described in Asia in AD 500.

The Immune System and Our Bacteria

The vast majority of the human immune system is located in the gut, where immune cells undergo essential training to tolerate helpful bacteria and recognize pathogens. 80 percent of the immune system is located in the gut. Fenced off within the gut's mucus membrane, bacteria allow defensive cells to practice identifying foreign structures without harming you. Immature immune cells that fail to distinguish between body tissue and external elements are eliminated during boot camp training before entering the bloodstream.

Experiments with germ-free mice reveal that a lack of microbial colonization leads to severe structural, metabolic, and behavioral abnormalities. Completely sterile laboratory mice exhibit hyperactive behavior, lack of caution, enlarged appendixes, shriveled digestive tracts with sparse villi, and reduced immune cells. Introducing specific bacteria or fecal transplants from other subjects can partially or fully reverse these deficiencies.

A baby's initial gut colonization depends heavily on the method of birth and early contact with maternal microbes and breast milk. Vaginally born infants are coated in protective maternal bacteria dominated by Lactobacillus, whereas cesarean-section infants acquire skin-derived environmental germs and face higher risks of allergies and asthma. Breast milk supplies essential antibodies and specialized nutrients like Bifidobacteria that fuel proper metabolic and immune development.

Over a third of all children in Western countries are born by cesarean section. Three-quarters of newborns who pick up typical hospital germs are born by cesarean section. It takes 3 years for infant gut flora to develop and stabilize.

Gut microbes contribute significantly to human nutrition by predigesting complex food components and synthesizing essential vitamins. In the industrialized world, 90 percent of nutrition comes from direct food intake, while 10 percent is supplied by bacteria. They break down complex plant carbohydrates and create vitamins that your own human cells cannot synthesize.

Fresh cabbage contains fewer vitamins than sauerkraut because bacteria manufacture extra vitamins during fermentation.

• Choose supermarket yogurt that explicitly states it contains mainly dextrorotatory lactic acid.

4. The Brain-Gut Connection

The primary evolutionary reason animals have a brain is to enable and coordinate physical movement. Sessile animals like the sea squirt eat their own brain immediately after settling down on a secure rock for the rest of their life. Everything the brain does serves to produce or suppress movement.

The vagus nerve serves as the fastest and most important physical communication highway connecting the gut to the brain.

Signals from the gut travel up the vagus nerve to influence key emotional, motivational, and fear-processing centers in the brain. In an experiment by John Cryan's team, mice fed with the probiotic bacterium Lactobacillus rhamnosus (JB-1) exhibited reduced stress hormones, increased motivation, and better memory; however, severing their vagus nerve completely eliminated this behavioral difference. The European Union approved vagus nerve stimulation treatment for depressive disorders in 2010.

Chronic stress forces the brain to divert energy away from the gut, weakening its protective mucus layer and altering its bacterial balance. When the brain perceives prolonged emergency situations or time pressure, it borrows energy from the gut via sympathetic nerve fibers.

Hypnotherapy can effectively retrain hypersensitive nerves in the gut and significantly reduce abdominal pain for irritable bowel syndrome sufferers. For children with irritable bowel syndrome, hypnotherapy has been shown to produce a 90-percent reduction in pain compared to a 40-percent reduction achieved by standard drugs.

• Ensure the chosen hypnotherapist is recognized by a reputable institution.
• Use guided imagery and thought journeys to reduce pain signal intensity and alter stimulus processing.

Human self-awareness and feeling maps originate in the insular cortex, which synthesizes internal bodily signals from organs like the gut. Bud Craig spent 20 years staining nerve fibers and tracking their paths to demonstrate that the insula receives physical data streams and refreshes its feeling picture approximately every forty seconds.

Update on the Brain-Gut Connection

Certain gut bacteria, known as psychobiotics, can gradually influence human emotional states and reduce tendencies toward anger and brooding. Twenty reliable studies involving human subjects have explored psychobiotics, noting a three to four weeks delay before bacterial effects on emotional state often appear.

A French study investigated a combination of Bifidobacterium longum and Lactobacillus helveticus, finding that test subjects experienced positive improvements in depressive tendencies, anger parameters, and the perception of physical aches after four weeks. A Dutch team using a daily bacteria mixture for four weeks found that subjects improved their scores in anger and brooding by at least 10 percent from an average baseline score of 43 out of 136 points. Three weeks of Lactobacillus casei Shirota improved the disposition of ill-tempered subjects.

Specific probiotic strains can help reduce physical and subjective stress symptoms, particularly in sleep-deprived individuals. In a study of 581 subjects divided into four groups, those given Bifidobacterium bifidum felt slightly less stressed during exam periods compared to peers who slept equally badly but did not receive the bacterium. Lactobacillus helveticus and Bifidobacterium infantis did not produce this specific stress-reduction effect.

Bifidobacterium longum 1714 reduces day-to-day stress, lowers stress hormone levels during acute stress, and improves memory performance. Irish researchers tested Bifidobacterium longum 1714 on humans who wore an electrode helmet, plunged their hands into ice-cold water, and solved mental puzzles on a tablet PC. Participants achieved 15 percent lower levels of day-to-day stress compared with the placebo group and made two to five fewer mistakes in memory tasks.

• Put on a funny helmet.
• Plunge one of your hands into ice-cold water.
• Solve mental puzzles on a tablet PC.

The gut plays a measurable partial role of 10 to 15 percent in mood and stress, but its exact involvement in recovering from fully fledged clinical depression is still being researched. Irish researchers harvested gut bacteria from people with depression and implanted them into rats whose own microbes were first removed, causing the rats to develop depressive behaviors. Scientists investigated probiotic bacteria on depression in a 2015 study and a 2017 study, utilizing the twenty-one questions included in the Becks Depression Inventory psychometric test.

5. Diet, Parasites, and Cleanliness

Maintaining digestive health requires understanding dietary fiber, managing harmful parasites and bacteria, and practicing smart cleanliness alongside targeted probiotics.

Harmful Bacteria and Parasites

Salmonella bacteria enter the food chain primarily through contaminated animal feed and poultry processing. They survive freezing temperatures easily, but exposure to 167 degrees Fahrenheit for ten minutes kills all Salmonella bacteria.

• Always use plastic chopping boards because they are easier to clean properly and provide fewer grooves and ridges for bacteria to hide in.
• Always wash anything that comes into contact with raw meat or eggshells thoroughly with hot water—chopping boards, hands, cutlery, kitchen sponges, and colanders, for example.
• Whenever possible make sure that meat and egg-based foods are cooked through, and use good-quality, fresh eggs stored below 50 degrees Fahrenheit.
• Think beyond the kitchen and wash hands properly after handling pet reptiles like iguanas.

Helicobacter pylori is a bacterium that colonizes the human stomach. It survives acid by neutralizing it and burrowing into the mucus membrane. At least half of humankind harbor this bacterium.

• Test patients with stomach complaints by giving them a fluid to drink and identifying marked, odorless gas in their breath using a special machine if H. pylori is present.

Toxoplasma gondii parasites reproduce in cats and use intermediate hosts like rats and humans. Active infections increase traffic accident risks and deplete serotonin precursors.

• Change cat litter every day if there is a pregnant woman in the house, ensuring she does not handle it.
• Avoid raw food and always wash fruit and vegetables thoroughly to prevent toxoplasma transmission.

Pinworms are common gut parasites that migrate to the anus at night to lay eggs. This induces itching that prompts scratching and transfers eggs back to your mouth.

• Spread cheeks, stick tape to the anus and the surrounding area in the morning, pull it off, and bring it to the doctor for examination.
• Change bedclothes and underwear every day, washing them at 140 degrees Fahrenheit or hotter.
• Practice regular hand washing and treat intense itching with creams rather than scratching.

Smart Cleanliness and Probiotics

Smart cleanliness aims to reduce bacteria numbers rather than annihilate them. You maintain a healthy equilibrium of beneficial and harmless microbes through measured habits.

• Dilution: wash fruit and vegetables to dilute soil-dwelling bacteria, or air out rooms.
• Drying: keep surfaces, armpits, and food dry because bacteria cannot breed on dry surfaces.
• Temperature: refrigerate food below 41 degrees Fahrenheit and wash contaminated laundry at 140 degrees Fahrenheit or more.
• Cleaning: remove fat and protein films using water and cleaning fluid.

Antibiotics are powerful weapons that kill dangerous pathogens along with vast numbers of helpful gut bacteria. One in four people in Germany take antibiotics once a year on average.

• Do not take antibiotics unless it is really necessary, such as for severe pneumonia.
• Always complete the full course of antibiotics if prescribed.
• Choose organically farmed meat to avoid resistant bacteria bred by agricultural antibiotic use.
• Wash fruit and vegetables thoroughly to avoid consuming tiny amounts of antibiotic residues.
• Take special care abroad in bacterial problem countries and cook it, peel it, or leave it.

Probiotics are edible living bacteria that help restore a healthy balance in the gut. They are delivered through fermented foods and targeted supplements.

• Try probiotic products for about four weeks to test their effectiveness.
• Check that the product is within its best-before date and contains the specific bacterial strain targeted for your complaint.

Prebiotics are specialized dietary fibers that pass undigested into the large intestine to nourish beneficial bacteria exclusively.

• Gradually increase dietary fiber intake rather than switching abruptly to avoid overproduction of gas.
• Include prebiotic foods such as leeks, asparagus, onions, garlic, endives, salsify, artichokes, and cooled potatoes or rice.

Fermenting vegetables at home using salt and natural bacteria is a safe and effective way to prepare food. You can use simple ingredients to support your gut health.

• Select vegetables like cabbage or carrots that have not been treated with pesticides.
• Slice thinly or grate for a one-week fermentation time, or leave whole for four to six weeks.
• Add one-third of an ounce to half an ounce of salt for every 2.2 pounds of vegetables, avoiding iodized salt.
• Knead the mixture thoroughly to mix the salt, break down tough cell walls, and extract water.
• Press the cabbage firmly into an airtight jar ensuring all vegetable matter is submerged beneath the liquid.
• Add a clean boiled rock, stone, or special weight if needed to keep vegetables pressed down beneath the liquid level.

10 Key Ideas

1. The intestinal tube forms the core of human embryonic development, while the mouth, esophagus, and stomach feature sophisticated anatomical structures to process food and protect health.
2. Squatting is the anatomically natural position for defecation and prevents excessive strain on the gut.
3. The enteric nervous system operates the digestive tract with complete autonomy, coordinating transport, swallowing, and emergency defense programs like vomiting.
4. Microscopic folds, villi, and microvilli in the small intestine create a massive surface area equivalent to about 4.5 miles in length.
5. The vagus nerve serves as the fastest and most important physical communication highway connecting the gut to the brain.
6. Human gut microbiomes organize into three distinct enterotypes dominated by specific bacterial families regardless of age or gender.
7. Skewed proportions within the gut's bacterial community have been linked to obesity, malnutrition, and chronic digestive disorders.
8. Helicobacter pylori is a bacterium that colonizes the human stomach and survives acid by neutralizing it and burrowing into the mucus membrane.
9. Antibiotics are powerful weapons that kill dangerous pathogens along with vast numbers of helpful gut bacteria.
10. Certain gut bacteria, known as psychobiotics, can gradually influence human emotional states and reduce tendencies toward anger and brooding.