Gas and bloating: common causes and when to see a doctor

Gas is a normal part of digestion. Everyone has gas in the digestive tract, and many people are bothered by it once in a while. Bloating, a feeling of fullness or swelling in the belly, is common too: research summarised by the US National Institutes of Health (NIH) suggests that between 16% and 31% of people experience it.

Most of the time gas is harmless, and small changes to how and what you eat can make a difference. Sometimes, though, it is a sign of something that needs a doctor. Below: where gas comes from, what adds to it, and which symptoms should not wait.

How much gas is normal?

According to the NIH, people pass gas an average of 8 to 14 times a day, and experts consider up to 25 times a day to be normal. People also typically burp up to 30 times a day. Having some gas is normal, especially during or after meals.

What counts as normal differs from person to person, as the UK's National Health Service (NHS) points out. Gas becomes a problem when it happens often, bothers you or gets in the way of your daily life, or when you notice a change from what is usual for you.

Is bloating the same as a swollen tummy?

Not always. Doctors separate a few things that often share one name:

• Burping is gas leaving the stomach through the mouth.
• Passing gas, or flatulence, is gas leaving through the back passage. A strong smell may come from sulphur in the gas.
• Bloating is the feeling that your tummy is full or swollen.
• Distension is when the tummy actually becomes larger than usual. Only about half of people with bloating also have distension.

The NHS lists the usual signs of bloating as a tummy that feels full or bigger than usual, tummy pain or discomfort, rumbling noises, and passing more gas than usual.

Where does the gas come from?

The NIH describes two main sources: air you swallow, and bacteria in your large intestine breaking down food that was not fully digested earlier on.

Swallowed air. Everyone swallows a little air when eating and drinking. Some of it leaves again when you burp; air that does not can move on into the intestines. You swallow more air when you:

• chew gum or suck on hard sweets;
• drink fizzy drinks;
• eat or drink too fast;
• smoke;
• wear dentures that are loose.

Carbohydrates your gut does not fully digest. Some foods contain sugars, starches and fibre that the stomach and small intestine do not fully break down. They pass to the large intestine, where bacteria break them down and create gas in the process. Eating more of these foods can mean more gas symptoms.

The NHS names a lot of gas in the gut as the usual reason for bloating.

Which foods commonly cause gas?

The foods below are on the lists of the NIH and the NHS. This is not a list of foods to cut out: they are everyday foods, and gas symptoms vary from person to person.

For some people, a lot of fibre or high-fat foods add to symptoms too, and the NHS suggests going easy on processed, sugary, spicy and fatty foods.

Can a health condition cause gas and bloating?

Yes. The NIH and the NHS both list health conditions that can cause more gas, or make normal amounts of gas feel worse:

• Irritable bowel syndrome (IBS) and other functional gut disorders, which are linked to how the brain and the gut work together.
• Problems digesting certain sugars, such as lactose intolerance (symptoms after foods or drinks that contain lactose, a sugar found naturally in milk and milk products) and dietary fructose intolerance.
• Coeliac disease, for which doctors may recommend a gluten-free diet.
• Constipation.
• Small intestinal bacterial overgrowth, a change in the bacteria of the small intestine.

Some people also feel bloated around the time of their period. Some medicines can cause extra gas, including anti-inflammatory painkillers such as ibuprofen, some laxatives, antifungal medicines and statins; do not stop or change a medicine without speaking to your doctor first. And bloating that does not go away can, now and then, be a sign of something more serious, such as ovarian cancer.

The NHS puts it plainly: do not self-diagnose. If you think a condition may be behind your symptoms, talk to a doctor about your diet before cutting foods out.

What everyday habits can help?

These suggestions come from the NHS and the NIH:

• Eat smaller meals more often, instead of a few large ones.
• Eat slowly. Chew with your mouth closed, avoid talking while you eat, and sit down for meals when you can.
• Cut down on chewing gum, hard sweets, fizzy drinks and drinking through a straw.
• Drink plenty of water, and go easy on alcohol and on the caffeine in coffee and tea.
• Exercise regularly.
• Avoid large meals late at night before bed, and do not slouch while eating.
• Peppermint tea is on the NHS list of things to try.
• When you feel bloated, gently massaging your tummy from right to left can help release trapped wind.
• If you are constipated, foods high in soluble fibre, such as oats or linseed, can help.
• If your dentures feel loose, ask your dentist to check the fit.

A pharmacist can also talk you through options you can buy and tell you whether you should see a doctor.

How can a food diary help?

Your doctor may ask you to keep a food and symptom diary. The NIH suggests writing down what you eat and drink and when your gas symptoms happen. The diary can show whether particular foods or drinks are linked to your symptoms, and help your doctor work out whether you have extra gas or are more sensitive to normal amounts.

Take it with you. Your doctor will also ask about your symptoms, your eating habits, any medical conditions, and the prescription and over-the-counter medicines and supplements you take. If a condition is found, your doctor or a registered dietitian may suggest an eating plan that suits it.

When to see a doctor

Gas is usually nothing to worry about. But the NHS and the NIH advise seeing a doctor if:

• gas or bloating bothers you or affects your daily life;
• your symptoms change suddenly;
• you feel bloated regularly, or keep feeling bloated after changing your diet;
• you have a stomach ache or bloating that does not go away or keeps coming back;
• you also have tummy pain, constipation or diarrhoea, or these keep coming back;
• you are losing weight without trying;
• you notice blood in your poo.

For women, frequent bloating deserves a check. The NHS lists feeling bloated or having a swollen tummy frequently, roughly 12 or more times a month, among the main symptoms of ovarian cancer. These symptoms are common and can be caused by many different conditions, but it is still important to have them checked.

Get medical advice urgently, the same day, if you have bloating together with vomiting, diarrhoea or constipation; a stomach ache; a high temperature, or feeling hot, cold or shivery; a swelling or lump in your tummy; a burning feeling in your chest from acid coming up; or if you cannot pee, poo or pass gas.

Call your local emergency number or go to an emergency department if your tummy is swollen and you have a severe stomach ache that came on very suddenly, you are vomiting blood or your vomit looks like ground coffee, or you have severe difficulty breathing.