A gut-friendly everyday life

Exercise, sleep, social contact and breaks: what your gut picks up from the rest of your life.

How solid is the research? Promising

That stress worsens gut symptoms is well established. How strongly sleep, exercise and social contact change the microbiome itself has only been studied in smaller studies in humans.

Healthy state

The gut has its own nervous system with hundreds of millions of nerve cells, more than the spinal cord. It controls movement, secretions and blood flow largely by itself and is in constant exchange with the brain via the Vagus nerve The tenth cranial nerve and the most important nerve of the rest-and-digest system. It connects the brainstem and the abdominal organs; most of its fibres tell the brain what is happening in the gut. More in the chapter “The vagus nerve: the data line between belly and head”, hormones and immune signals. The exchange runs in both directions, but most fibres report from the gut to the brain. That is why excitement hits the stomach, and why the brain notices when the gut is irritated.

Digestion begins in the head. Seeing, smelling and tasting food trigger saliva, stomach acid and pancreatic juices via the vagus nerve before the first bite is down; this cephalic phase prepares the gut. If you eat calmly and chew well, you break food down mechanically, mix in salivary enzymes and swallow less air. At rest, in balance between the sympathetic and parasympathetic system (the accelerator and brake of the autonomic nervous system), digestive juices flow, blood flow is right and gut movement is even.

Between meals, a Migrating motor complex A wave of muscle contractions that sweeps the stomach and small intestine empty about every one and a half to two hours when fasting. Eating interrupts it. More in the chapter “Intermittent fasting and meal timing: 16:8, 5:2 and Ramadan” runs through the small intestine about every hour and a half to two hours, the migrating motor complex (MMC). It sweeps leftovers and bacteria towards the colon and so protects against colonisation of the small intestine. It starts only after some hours without eating. If you constantly graze, you give it no chance; a break of three to four hours between meals gives it room. Sleep is part of this too, since it is particularly pronounced at night.

The gut also follows an internal clock. It is more active by day and quieter at night; in the morning after getting up and breakfast the gastrocolic reflex triggers the urge to go. Hormones such as cortisol and melatonin, and even the composition of the Microbiome, gut microbiota The community of all microbes in the gut, mainly bacteria, plus viruses, fungi and archaea. Most live in the colon. More in the chapter “Building microbial diversity”, fluctuate over the day. Exercise supports this mechanically and through hormones: a brisk walk stimulates gut activity, and in one study endurance training also changed the gut microbiota, independent of diet. And people who spend a lot of time together share gut bacteria, even outside the family. The microbiome is therefore not just private but shared with the surroundings.

Regular meals and sleep: gut movement runs calmly and evenly.

Disrupted state: causes and effects

Constant stress, too little sleep and eating on the go keep the body in alarm mode. The sympathetic system (the “accelerator” side) and stress hormones such as corticotropin-releasing hormone throttle digestive juices and blood flow to the gut, speed up or slow down movement depending on the person, and activate Mast cells Immune cells beneath the skin and mucous membranes, filled with histamine and other messengers. They raise the alarm in allergies, infections and stress. More in the chapter “Mast cells: alarm cells in the gut, histamine and the disputed MCAS” in the gut wall. Studies in humans and animals show that stress can make the gut more permeable and more sensitive to stimuli it would otherwise barely notice. That is why excitement turns into diarrhoea in some people and constipation in others.

Sleep and gut influence each other. A Meta-analysis An analysis that combines the results of several studies. It is only as good as the studies it includes. of 36 studies found sleep disorders clearly more often in Irritable bowel syndrome Recurring abdominal pain linked to bowel movements, without tests finding another cause. Today it is understood as a disorder of gut–brain interaction. More in the chapter “The gut-brain axis” than in healthy people; those who sleep badly usually have more gut symptoms the next day, and symptoms in turn disturb sleep. Which direction dominates is hard to say in an individual. Shift work, changing sleep times and “social jet lag” (weekends completely different from weekdays) disturb the gut’s internal clock, as does late, heavy eating shortly before bed.

Constantly eating on the side has several consequences. If the cephalic phase is missing because you look at a screen, you chew less and swallow more air, which promotes belching and bloating. If you snack all day, you interrupt the cleansing wave: in people with irritable bowel syndrome and an abnormal Breath test After drinking a sugar solution, hydrogen and methane in the breath are measured several times. This can reveal sugar intolerances and signs of bacterial overgrowth. More in the chapter “Gut tests: what they show and what they do not”, fewer such waves were measured, which fits the tendency for bacteria to persist in the small intestine. The urge to go is often ignored for lack of time; repeated suppression can promote constipation. Lack of exercise also contributes to sluggish gut movement. Too much of a good thing is possible as well: very intense endurance exercise diverts blood from the gut to the muscles and causes diarrhoea and cramps in some people.

As for the microbiome, the evidence remains cautious. A systematic review of 13 human studies found links between psychological stress and the gut microbiota but no uniform change; much comes from animal studies. It is worth countering a misunderstanding: “Your stress broke your gut” is too simple. Irritable bowel usually arises from several factors, including infections, diet and predisposition; daily life and stress are amplifiers, not the only cause. It differs by person: women are affected more often, hormonal fluctuations can shape symptoms, and with age gut movement often becomes more sluggish.

Constant snacking and ongoing stress: gut movement becomes restless.

What often helps

Lifestyle

Diet, exercise, sleep, social contact and dealing with stress.

Daily exercise A brisk walk or cycling stimulates gut activity. In one study, just a few weeks of endurance training measurably changed the gut microbiota. What counts is regularity; with a sensitive gut, moderate effort is often better tolerated than very hard sessions. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [1]
Regular sleep times The gut follows a daily rhythm. Regular sleep and meal times help it keep this rhythm. Do not eat dinner too late or too heavy, so that the cleansing wave can work at night. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [2]
Human closeness People who spend a lot of time together share gut bacteria, even outside the family. Whether that makes you healthier is open, but it shows how social the microbiome is. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [3]
Eat calmly Eat slowly, chew well and leave three to four hours between meals. Put the screen away and take two or three breaths before the first bite so that the cephalic phase can work. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [4][5]
Take the urge to go seriously In the morning after breakfast and coffee the gastrocolic reflex is strongest: plan time for it and give in to the urge instead of suppressing it. A routine forms after a few weeks. Promising How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
Small islands of relaxation Breathing exercises with a long exhale, walks, singing or conversation activate the brake of the autonomic nervous system. Two to three minutes before or between meals are enough to start; more in the chapter on the vagus nerve. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.

Natural supplements

Supplements do not replace a medical check-up. Discuss dosage and interactions with your doctor or pharmacist.

Magnesium Magnesium oxide and citrate have a laxative effect and are used for constipation. Good studies on relaxation or the gut microbiota are lacking. With reduced kidney function, discuss it with a doctor first. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
Soluble fibre for constipation Psyllium husk as soluble fibre is recommended for irritable bowel syndrome and constipation, whereas insoluble bran is rather not. Start slowly and drink plenty, otherwise you will bloat. Promising How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [6]

Medical treatments

Information, not a treatment recommendation. Decide together with a doctor. Approval and availability differ from country to country.

Gut-directed psychotherapy Gut-directed hypnotherapy and cognitive behavioural therapy relieve IBS symptoms. The guideline suggests them even when there is no mental illness. Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [6]
Have sleep problems checked too If you sleep badly for a long time, have causes such as sleep apnoea, restless legs or depression checked. Better sleep often eases gut symptoms too, and that is a route of treatment in its own right. Promising How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [7]

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How we rate the evidence

Trust score 5 of 5:Established: Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies.
Trust score 4 of 5:Well supported: Several randomised studies in humans with largely consistent results.
Trust score 3 of 5:Promising: Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies.
Trust score 2 of 5:Plausible: Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms.
Trust score 1 of 5:Experimental: Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.

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