Gas-Related Symptoms

Belching (eructation) results from swallowed air or from gas generated by carbonated beverages. Aerophagia occurs normally in small amounts during eating and drinking, but some people unconsciously swallow air repeatedly while eating or smoking and at other times, especially when anxious or in an attempt to induce belching. Excessive salivation increases aerophagia and may be associated with various gastroesophageal (GI) disorders (eg, gastroesophageal reflux disease), ill-fitting dentures, certain medications, gum chewing, or nausea of any cause.

Most swallowed air is eructated. Only a small amount of swallowed air passes into the small bowel; the amount is apparently influenced by position. In an upright person, air is readily belched; in a supine person, air trapped above the stomach fluid tends to be propelled into the duodenum. Excessive eructation may also be voluntary; patients who belch after taking antacids may attribute the relief of symptoms to belching rather than to antacids and may intentionally belch to relieve distress.

A rare cause of excessive belching is supragastric belching. In supragastric belching, a rapid entry of air into the esophagus is expelled after tensing the abdomen. It may occur under volition or unconsciously and can severely affect quality of life (1).

Abdominal bloating may occur in isolation or along with other GI symptoms in patients with functional disorders (eg, aerophagia, nonulcer dyspepsia, gastroparesis, irritable bowel syndrome) or organic disorders (eg, ovarian cancer, colon cancer). Gastroparesis (and consequent bloating) also has many nonfunctional causes, the most important of which is autonomic visceral neuropathy due to diabetes; other causes include postviral infection, medications with anticholinergic properties, and long-term opioid use. However, excessive intestinal gas is not clearly linked to complaints of distention and bloating. In most healthy people, 1 L/hour of gas can be infused into the gut with minimal symptoms. It is likely that many symptoms are incorrectly attributed to “too much gas.”

On the other hand, some patients with recurrent GI symptoms often cannot tolerate small quantities of gas: Retrograde colonic distention by balloon inflation or air instillation during colonoscopy often elicits severe discomfort in some patients (eg, those with irritable bowel syndrome) but minimal symptoms in others. Similarly, patients with eating disorders (eg, anorexia nervosa, bulimia nervosa) often misperceive and are particularly stressed by symptoms such as bloating. Thus, the basic abnormality in patients with gas-related symptoms may be a hypersensitive intestine. Altered motility may contribute further to symptoms.

There is great variability in the quantity and frequency of rectal gas passage. As with stool frequency, people who complain of flatulence often have a misconception of what is normal. The average number of gas passages is about 13 to 21/day. Objectively recording flatus frequency (using a diary kept by the patient) is a first step in evaluation.

Flatus is a metabolic byproduct of intestinal bacteria; almost none originates from swallowed air or back-diffusion of gases (primarily nitrogen) from the bloodstream. Bacterial metabolism yields significant volumes of hydrogen, methane, and carbon dioxide.

Hydrogen is produced in large quantities in patients with malabsorption syndromes and after ingestion of certain fruits and vegetables containing indigestible carbohydrates (eg, baked beans), sugars (eg, fructose), or sugar alcohols (eg, sorbitol). In patients with disaccharidase deficiencies (most commonly lactase deficiency), large amounts of disaccharides pass into the colon and are fermented to hydrogen. Celiac disease, tropical sprue, pancreatic insufficiency, and other causes of carbohydrate malabsorption should also be considered in cases of excess colonic gas.

Methane is also produced by colonic bacterial metabolism of the same foods (eg, dietary fiber). However, about 10% of people have bacteria that produce methane but not hydrogen.

Carbon dioxide is also produced by bacterial metabolism and is generated in the reaction of bicarbonate and hydrogen ions. Hydrogen ions may come from gastric hydrochloric acid or from fatty acids released during digestion of fats—the latter sometimes produces several hundred milliequivalents of hydrogen ions. The acid products released by bacterial fermentation of unabsorbed carbohydrates in the colon may also react with bicarbonate to produce carbon dioxide. Although bloating may occasionally occur, the rapid diffusion of carbon dioxide into the blood generally prevents distention.

Diet accounts for much of the variation in flatus production among individuals, but poorly understood factors (eg, differences in colonic flora and motility) may also play a role.

Despite the flammable nature of the hydrogen and methane in flatulence, working near open flames is not hazardous. However, gas explosion, even with fatal outcome, has been reported during jejunal and colonic surgery and colonoscopy, when diathermy was used during procedures in patients with incomplete bowel cleaning.

1. 1. Koukias N, Woodland P, Yazaki E, Sifrim D: Supragastric belching: Prevalence and association with gastroesophageal reflux disease and esophageal hypomotility. J Neurogastroenterol Motil 21(3):398–403, 2015. doi: 10.5056/jnm15002

History of present illness in patients with belching should be directed at finding the cause of aerophagia, especially dietary causes.

In patients complaining of gas, bloating, or flatus, the relationship between symptoms and meals (both timing and type and amount of food), bowel movements, and exertion should be explored. Certain patients, particularly in the acute setting, may use the term "gas" to describe their symptoms of coronary ischemia. Changes in frequency and color and consistency of stool are sought. History of weight loss is noted.

Review of systems should seek symptoms of possible causes, including diarrhea and steatorrhea (malabsorption syndromes such as celiac sprue, tropical sprue, disaccharidase deficiency, and pancreatic insufficiency) and weight loss (cancer, chronic malabsorption).

Past medical history should review all components of the diet for possible causes (see table Some Causes of Gas-Related Symptoms).

The examination is generally normal, but in patients with bloating or flatus, signs of an underlying organic disorder should be sought on abdominal, rectal, and (for women) pelvic examination.

The following findings are of concern:

• Weight loss

• Blood in stool (occult or gross)

• "Gas" sensation in chest

Chronic, recurrent bloating or distention in a patient with abdominal pain that is related to defecation and associated with change in frequency or consistency of stool but without red flag findings suggests irritable bowel syndrome.

Long-standing symptoms in an otherwise well young person who has not lost weight are unlikely to be caused by serious physiologic disease, although an eating disorder should be considered, particularly in young women. Bloating accompanied by diarrhea, weight loss, or both (or only after ingestion of certain foods) suggests a malabsorption syndrome.

Testing is not indicated for belching unless other symptoms suggest a particular disorder.

Testing for carbohydrate intolerance (eg, lactose, fructose) with breath tests should be considered particularly when the history suggests significant consumption of these sugars. Testing for small intestinal bacterial overgrowth should also be considered, particularly in patients who also have diarrhea, weight loss, or both, preferably by aerobic and anaerobic culture of small-bowel aspirates obtained during upper GI endoscopy. Testing for bacterial overgrowth with hydrogen breath tests, generally glucose-hydrogen breath tests, is prone to false-positive (ie, with rapid transit) and false-negative (ie, when there are no hydrogen-producing bacteria) results. Testing for rare conditions such as sucrase-isomaltase deficiency can be considered in patients with refractory or severe symptoms (1).

New, persistent bloating in middle-aged or older women (or those with an abnormal pelvic examination) should prompt pelvic ultrasonography to rule out ovarian cancer.

1. 1. Husein DM, Rizk S, Naim HY: Differential effects of sucrase-isomaltase mutants on its trafficking and function in irritable bowel syndrome: Similarities to congenital sucrase-isomaltase deficiency. Nutrients 13(1):9, 2021. doi: 10.3390/nu13010009

1. 1. Moshiree B, Drossman D, Shaukat A. AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention: Expert Review. Gastroenterology. 2023;165(3):791-800.e3. doi:10.1053/j.gastro.2023.04.039