Gas and Bloating

Why it happens, when it matters, and how it can be eased.

What are gas and bloating?

Gas and bloating of the abdomen are extremely common complaints. Most of the time they are not the sign of a serious disease; but if they last a long time, disturb daily life or come with other symptoms, the cause may need investigating.

Gas means the air and other gases in the digestive system. It leaves the body by belching from the mouth or by passing from the bowel.

Bloating is the feeling of fullness, pressure or tightness in the abdomen.

There is an important distinction here:

Feeling bloated does not necessarily mean there is a large amount of gas in the abdomen.

In some people the amount of gas is normal, yet marked bloating is felt because the bowel is more sensitive to a normal amount of gas. Where the girth of the abdomen genuinely increases visibly, this is called abdominal distension. According to the NIDDK, only about half of the people who experience bloating also have visible distension.

How is gas formed in the bowel?

There are two main sources of gas in the digestive system.

1. Swallowed air

We all swallow some air while eating and drinking.

In particular:

• Eating very fast,
• Chewing gum,
• Fizzy drinks,
• Drinking through a straw,
• Smoking

can increase the amount of air swallowed. Some of it leaves by belching; the rest may pass on into the bowel.

2. Gas made by bowel bacteria

Some of the carbohydrates we eat cannot be fully digested and absorbed in the small intestine.

When they reach the large bowel they are broken down by the bowel bacteria. Gas is formed during this process, which is called fermentation.

This is in fact part of normal digestion.

Is passing wind normal?

Yes.

Passing wind is a normal function of a healthy digestive system.

Studies report that people pass bowel gas on average about 8–14 times a day, and that in some healthy people passing wind up to 25 times may still be within normal limits.

So what matters is not only “how many times you pass wind”.

It matters more if the gas is new, has increased markedly, causes pain, or comes with other symptoms.

What are the commonest causes of bloating?

There is no single cause. Sometimes several mechanisms act together.

Diet

More gas may be formed while some foods are being digested.

In particular:

• Dried beans, chickpeas and lentils,
• Onion and garlic,
• Cabbage, broccoli and cauliflower,
• Some fruits,
• Some cereal products,
• Fizzy drinks,
• Some artificial sweeteners

may increase gas and bloating in some people.

But it is not right to forbid all of these foods to everyone.

A food that troubles one person may cause no problem at all in another.

Lactose intolerance

When the lactose in milk cannot be digested well enough, it reaches the large bowel and is fermented by bacteria.

The result may be:

Bloating + gas + abdominal pain + diarrhoea

Lactose intolerance and milk allergy are not the same condition.

Coeliac disease

Gas and bloating may also be seen in coeliac disease.

But bloating alone does not mean coeliac disease is present.

If coeliac disease is suspected, it is important that the person does not start a gluten-free diet on their own initiative before testing; doing so can affect the results of the coeliac tests.

Irritable bowel syndrome (IBS)

Gas and bloating are quite common in IBS.

In some patients with IBS the problem may be less that a great deal of gas is produced than that the bowel perceives a normal amount of gas more strongly.

Communication between the brain and the bowel, and the pattern of bowel movements, may also play a part in the feeling of bloating.

For this reason simply telling the patient:

“Do not eat foods that cause gas.”

is not always enough.

Does constipation cause bloating?

Yes.

Constipation is one of the very common causes of gas and bloating.

Slowing of the passage of bowel contents and the accumulation of stool can produce fullness and bloating in the abdomen.

In these people, correcting the constipation may be more effective than trying to treat the gas alone. The AGA also recommends considering treatment directed at constipation in patients with bloating who are constipated.

Does SIBO cause gas and bloating?

Yes, in some patients.

SIBO means an abnormal increase in the number or distribution of bacteria in the small intestine.

It can cause symptoms such as gas, bloating, abdominal discomfort and diarrhoea.

But there is an important point:

Not everyone with gas and bloating needs to be investigated for SIBO.

The AGA recommends that SIBO tests be used only in patients with appropriate risk factors and clinical suspicion.

So the approach that has become widespread on the internet — “I am bloated, so I must have SIBO” — is not correct.

Can gas and bloating come from stomach conditions?

Yes.

Fullness and bloating in the upper abdomen after meals in particular may be associated with:

• Functional dyspepsia,
• Gastroparesis,
• Certain stomach conditions.

Reflux and belching may also sometimes accompany complaints of bloating.

For this reason whether the bloating is in the upper or the lower abdomen, its relation to meals, and whether it changes after opening the bowels can help in the diagnosis.

How is the diagnosis made?

Gastroscopy, colonoscopy or a scan is not needed for every complaint of gas and bloating.

Assessment begins first with:

how long the symptoms have been present + their relation to meals + bowel habit + medication + accompanying symptoms + physical examination.

If thought necessary, blood or stool tests, coeliac tests, breath tests for particular carbohydrate intolerances, or other investigations may be carried out.

Endoscopy and imaging are considered particularly in patients with alarm features, recent deterioration or an abnormality on examination. The AGA likewise does not recommend imaging or endoscopy routinely for everyone.

How can gas and bloating be reduced?

The cause should be sought first.

Simple measures may help many people:

• Eating slowly and chewing well,
• Avoiding very large portions,
• Cutting down fizzy drinks,
• Chewing less gum,
• Taking regular physical activity,
• Correcting constipation if present,
• Noticing which foods increase the complaint.

Keeping a food and symptom diary may make it easier for some patients to identify trigger foods.

Is a low-FODMAP diet necessary?

Not everyone with bloating needs to start a low-FODMAP diet.

But a short, controlled low-FODMAP approach may help some patients with marked bloating associated with IBS in particular.

This diet does not mean forbidding all FODMAP-containing foods for a long period. Where needed, foods are reintroduced in a controlled way after elimination, so that the foods the person is genuinely sensitive to can be identified.

The AGA recommends that restrictive diets of this kind be carried out where needed with a dietitian experienced in gastrointestinal disease.

Do probiotics relieve gas and bloating?

There is a great deal of advertising and a great many different products in this field.

But it has not been shown that all probiotics have the same effect or that they reliably relieve bloating.

Indeed, the AGA’s clinical approach to gas, bloating and distension does not recommend the routine use of probiotics to treat abdominal bloating and distension.

It would therefore not be right for this site to recommend a particular probiotic as a “gas remedy”.

Can stress really cause bloating?

Yes. But this does not mean the complaint is psychological or imagined.

The brain and the bowel are in constant communication.

Stress, anxiety and changes in the sensitivity of the bowel can make a person perceive normal bowel movements and gas as more troublesome.

In some patients the coordination of the diaphragm and the abdominal wall muscles also changes, which can contribute to visible swelling of the abdomen.

For this reason diaphragmatic breathing, cognitive behavioural therapy and other brain-gut behavioural treatments may help selected patients.

Can gas and bloating be a sign of cancer?

Most of the time, no.

Gas and bloating are very common complaints and the great majority do not arise from cancer.

But where bloating that was not present before and is steadily increasing is accompanied by:

• Unintentional weight loss,
• Anaemia,
• Blood in the stool,
• Black stools,
• Persistent or increasing abdominal pain,
• Recurrent vomiting,
• A marked change in bowel habit

other underlying conditions should be investigated.

When should I see a doctor?

It is useful to have gas and bloating assessed if they are new, have become constant, are steadily increasing, or are markedly affecting your daily life. The NIDDK likewise recommends medical assessment if the symptoms change suddenly or are accompanied by other complaints such as pain, constipation, diarrhoea or weight loss.

Where there is weight loss, anaemia, bloody or black stools, persistent vomiting, fever or severe abdominal pain in particular, a doctor should be seen without delay.

In brief

Gas and bloating are not a disease in themselves but a symptom.

In most people they arise from benign causes such as diet, swallowed air, bowel movements and the sensitivity of the bowel to gas. In others, lactose intolerance, IBS, constipation, coeliac disease or other digestive conditions should be investigated.

The aim of treatment is not to forbid every “gas-forming” food, but to find the real cause of the complaint in that person and to avoid unnecessary restrictions.

This content is for general information. Diagnosis and treatment should be planned by a doctor according to the patient’s complaints and clinical features.

Currency: This was prepared taking account of the NIDDK’s current patient information and the American Gastroenterological Association’s (AGA) clinical practice update on Belching, Abdominal Bloating and Distention.