Your trousers fit the way they always do in the morning, until they start pressing against your belly by the evening and you notice getting up off the sofa that something has shifted over the course of the day. In between sat a perfectly ordinary day with coffee in the morning, lunch at your desk, two meetings and a beer after work, so nothing that would really explain the difference.

Bloating is one of those complaints almost everyone knows and hardly anyone mentions, even though somewhere between 15 and 30 per cent of adults report dealing with it regularly, depending on the survey. For many it stays an uncomfortable evening, while for others it shapes what they wear for weeks on end, how they plan their meals and sometimes whether they go out at all.

What follows sorts out what is actually happening in your abdomen, which everyday triggers sit behind it most often, what tends to be worth your effort and at what point a medical opinion makes sense.

Pressure inside and a bigger waistline are two separate things

Medicine keeps two observations apart that usually end up sharing a single word in everyday language. One is the sensation of tightness, pressure and fullness, meaning everything you notice yourself. The other is a measurably larger abdominal girth, the part other people can see. The two often turn up together, although in some people they appear separately: a few feel the pressure very clearly while almost nothing changes on the outside, and in others the belly visibly pushes forward across the day without hurting at all.

The distinction is useful to you because different mechanisms sit behind the two variants. It also explains why dietary advice does very little for some people, while breathing and posture suddenly make a noticeable difference.

Gas in the gut is routine business

Your gut produces gas every single day, because bacteria in the colon break down all those carbohydrates that weren't fully absorbed higher up. That releases mainly hydrogen and carbon dioxide, with methane on top in a proportion of people. Then there's the air you swallow while eating, drinking and talking, which also has to go somewhere afterwards.

Passing wind ten to twenty times a day counts as entirely unremarkable, even if that sounds like rather a lot at first. Spread across a whole day, most people simply never notice.

Here's something worth knowing: people with pronounced bloating often have much the same amount of gas in their abdomen as everyone else, which measurements confirm in plenty of cases. The difference lies in how sensitively the abdomen registers that volume and how the body responds to it mechanically.

Why your belly visibly grows over the course of the day

Perception. In many people with irritable bowel syndrome or recurrent bloating, sensitivity in the abdominal cavity is set higher, so a volume of gas others don't notice at all arrives as distinct pressure. This visceral hypersensitivity is well documented and a measurable property of the nervous system monitoring your abdomen.

The abdominal wall. Imaging studies show that filling in the abdomen sets off an unhelpful chain reaction in some people: the diaphragm descends while the front abdominal wall slackens at the same time, which gives the contents room towards the front and increases girth visibly, even though the amount of gas has stayed roughly the same. The clinical term for this is abdominophrenic dyssynergia. The way it usually runs, the diaphragm rises, the abdominal wall holds its tension and very little of it shows on the outside.

That's exactly why recurrent bloating is worth looking at through breathing and posture, ideally alongside specialist physiotherapy that works specifically with the abdominal wall and diaphragm.

The most common everyday triggers

Eating pace. Eating quickly, talking between bites and taking big gulps brings a lot of air along with it, which then travels through your digestive tract and makes itself felt by the evening at the latest.

Fizzy drinks and chewing gum. Sparkling water, beer and soft drinks deliver their gas directly. Gum and sweets have you swallowing more often, even with nothing arriving in your stomach.

Certain carbohydrates. Pulses, onions, garlic, cabbage, wheat products, stone fruit and some dairy contain sugars and fibres that are only partly absorbed in the small intestine and end up feeding your bacteria in the colon, which produces gas. All of these are foods that do your body good and belong on your plate. With a sensitive gut it's worth paying closer attention to portion size and spreading such foods across the day, because your gut handles smaller amounts considerably better.

Sugar substitutes. Sorbitol, xylitol, maltitol and erythritol turn up in sugar-free gum, sweets, protein bars and light products, where they're easy to miss while shopping. In larger amounts they have a laxative and gas-forming effect, which means a glance at the ingredients list sometimes delivers the whole explanation.

Fibre increased too quickly. Jumping from very little to a lot has your gut answering with bloating for the first few days, because the bacteria need a while to adjust to the new amount. Taken in small steps over two to four weeks, the same change goes far more smoothly.

Large meals late at night. Your gut works more slowly overnight, so a big portion shortly before bed sits around for longer and is often still noticeable the next morning.

Alcohol. It irritates the lining, changes the pace of things in the gut and, with beer and sparkling wine, brings gas of its own along too.

Stress and short nights. The link between head and gut is physically real, since stress measurably alters gut motility and too little sleep amplifies how loudly your abdomen reports every signal upwards.

Constipation. One of the most common reasons of all, because sluggish emptying leaves more material sitting in the bowel to ferment away quietly. Anyone wanting to get on top of their bloating is best off looking at their bowel habits first.

Movement. Even a walk after a meal gets the bowel muscles going noticeably, whereas long stretches of sitting slow the whole journey down.

Your cycle. In the second half of the cycle, progesterone slows bowel movement and fluid settles into the tissue on top of that. Plenty of people with a uterus know the belly that reliably goes up a size a few days before a period.

When something more is going on

With bloating that stays with you for weeks and months, a targeted work-up at your practice is worth it.

Lactose intolerance. Roughly 15 to 20 per cent of adults in Germany can only digest milk sugar to a limited degree, which typically shows up one to three hours after dairy with bloating, cramps and loose stool. A breath test at your practice brings clarity within a single appointment.

Fructose malabsorption. Here the uptake of fruit sugar in the small intestine is limited, which is why many people react to juices, dried fruit, honey and larger amounts of fruit, while small portions work perfectly well.

Coeliac disease. An autoimmune condition in which gluten damages the lining of the small intestine, affecting around one per cent of the population in Germany. The order of events matters here, since the diagnostics only work while you're still eating gluten. So get tested first, before you take anything off your plate.

Irritable bowel syndrome. Bloating is one of its cardinal symptoms, while IBS itself remains a diagnosis of exclusion, meaning other causes have to be off the table first. We've written at length elsewhere on the blog about how much it shapes your sex life too.

Bacterial overgrowth in the small intestine. Known as SIBO, a concept still debated among specialists, largely because testing methods remain inconsistent. If your belly swells right after eating and other symptoms come with it, that's a topic for a gastroenterology practice.

Thyroid and medication. An underactive thyroid measurably slows digestion, and several commonly prescribed agents slow the bowel as well, which shows up as pressure and fullness. If your symptoms started around the same time as a new treatment, raise it openly at your practice.

When you should get it medically assessed

The following warrant investigation:

• Weight loss you can't explain
• Blood in your stool, or black and tarry stool
• Symptoms that wake you at night
• Fever, persistent vomiting or severe pain
• Pallor, exhaustion or breathlessness as a possible sign of iron deficiency
• Bloating that is new, lasts for weeks and differs from your usual pattern
• New symptoms from around the age of 45
• Bowel cancer, coeliac disease or inflammatory bowel disease in your family
• Pain during sex that happens regularly

One thing we want to highlight in particular: if the belly stays swollen for several weeks in people with ovaries and pressure in the lower abdomen, feeling full very quickly or needing to pass urine more often come with it, that combination warrants a gynaecological assessment, since it occurs with ovarian cancer among other things. In the vast majority of cases a harmless explanation turns up. Guidelines still recommend a prompt assessment with exactly this combination of symptoms, because early clarification achieves a great deal here.

What helps in everyday life

Eat more slowly. The least spectacular measure with the best returns, because smaller bites, proper chewing and a fork put down in between noticeably reduce how much air goes along for the ride, which makes for a calmer evening.

Regular meals. Your gut likes routine, which is why three reliable meals work better for many people than constant snacking, where digestion never properly settles.

Build up fibre calmly. The guidance is at least 30 grams a day, and it's worth moving towards that in small steps while drinking enough alongside it, so the fibre can work at its best.

Movement after meals. Ten to fifteen minutes of walking is entirely enough and ranks among the best-supported measures against a feeling of fullness.

Support your bowel in emptying. As long as things get going reliably, less material is left behind to ferment. Fluids, fibre, movement and a fixed slot in the morning contribute most to that, because the bowel reflex is strongest for most people after breakfast. Following the urge as soon as it shows up helps as well, since the signal grows quieter over time when it keeps getting overridden.

Breathe into your belly. With abdominophrenic dyssynergia this works at exactly the right spot: lie flat, one hand on your belly, breathe in slowly through the nose, out even more slowly, for five minutes. With persistent symptoms, physiotherapy for the pelvic floor and abdominal wall can take that work further in a targeted way.

Warmth and massage. A hot water bottle or a clockwise circular massage relaxes the abdominal muscles, costs nothing and works within minutes for plenty of people.

Classic home remedies. Fennel, anise, caraway and peppermint as a tea tend to feel good with mild symptoms.

Elimination with a plan. If you want to try a structured dietary change, the usual candidate is a phase low in FODMAPs, meaning less of those sugars and fibres that ferment particularly strongly in the colon, from onions, wheat, pulses and stone fruit for instance. Keep it time-limited and do it with dietetic support, because the change runs in three phases and the third one, reintroducing foods step by step, is where the real insight comes from. Anyone who keeps cutting out more foods over months instead ends up with a very small range of meals that's hard to sustain day to day and strips the gut flora of the diversity it lives on.

A diary for two weeks. Note food, sleep, stress, bowel habits, cycle and symptoms roughly, and after a fortnight you'll see patterns that pass you by day to day. It's also the best preparation for a conversation at your practice.

Which leaves the question of how all this fits with the part further up, where pulses, cabbage and wholegrains appear as triggers. Both hold true at once, since fibre-rich foods do bring more gas with them in the first few weeks, while the bacteria in your colon adjust to the larger amount. Once that adjustment period is over, digestion runs more smoothly with them than on a low-fibre diet, where the journey slows down and stool stays firmer. So pace and portion size are what count: build up slowly, spread things across the day and drink enough alongside.

If fibre keeps falling short in everyday life, you can additionally build a supplement into your diet. That's exactly what Gut Feeling is made for, a daily gut routine in capsule form that Every Health developed together with clinicians from gastroenterology and nutritional research. The base is psyllium husk, a soluble plant fibre that binds water and adds bulk. Alongside it there's a well-researched bacterial strain, fennel seed, a fibre blend of baobab and acacia plus calcium from red algae, which contributes to the normal function of digestive enzymes. Drink a large glass of water with every dose so the fibre can work at its best, and start with a small dose if your gut is sensitive, because extra fibre can produce a little more gas in the first few days.

A balanced diet is something a supplement doesn't replace. Vegetables, pulses, fruit and wholegrains remain the foundation that most of this rests on.

A calm belly likes routine

For most people, bloating traces back to a handful of habits reinforcing one another, from eating fast through long days of sitting and large portions late in the evening to short nights and a bowel that empties sluggishly. Every one of those is something you can adjust and often one of them is enough to make the evening feel different.

Anything that sticks around for weeks or turns up as something new belongs in a practice. For everything else, what you mostly need is a bit of patience with your own belly, because your gut takes weeks rather than days to settle into new routines.