Bloating and Gas – Causes of Feeling Full and Gassy

What is bloating?

The term “bloating” refers to a feeling of fullness in the abdomen. The sensation of fullness may also be accompanied by a visible distension or swelling of the abdomen. The most common cause for bloating is a buildup of gas in the digestive tract. However, digestive gas usually does not cause distension of the adomen. Expulsion of gas through flatulence or belching often provides relief from the bloating sensation.

Bloating that is persistent may be due to causes that are unrelated to gas accumulation in the gastrointestinal tract. However, not all causes of persistent bloating are pathological in nature. For example, persistent abdominal distension may be caused by obesity. Abdominal distension may also be a result of pregnancy. As the uterus expands, the digestive organs in the vicinity may get compressed, leading to a bloating sensation.

Is it gas or fluid?

The cause of persistent abdominal bloating should be investigated since persistent abdominal distension may indicate an underlying pathology. For example, fluid accumulation in the abdominal or pelvic cavity (technically referred to as ascites) may cause abdominal distension and bloating.

Abdominal swelling in ascites may be caused by accumulation of blood or peritoneal fluid. A physical examination can help in distinguishing ascites due to fluid accumulation from abdominal bloating caused by accumulation of gas in the digestive tract. Ascites produces a sound of moving fluid, whereas accumulation of gas produces a hollow sound in the abdomen. X-ray, MRI, and ultrasound can also be used to establish the presence of ascites.

Gas that gets trapped within the left side of the transverse colon can cause bloating, cramping, and pain in the left abdomen and chest that may be confused with heart pain or pancreatic pain. This condition is technically referred to as the splenic-flexure syndrome.

Read more on excessive belching.

Source of Gas in the Gut

Gas in the gastrointestinal tract is produced by the combined action of various digestive processes (physical, chemical, and enzymatic) within the gut. The microbial flora that is present in the gut contributes to gas formation by fermenting the food and waste products in the gut. Gas inhaled or consumed through the mouth also contributes to the gas in the gut.

The accumulated gas in the gut can be expelled through belching (via the mouth) or flatulence (through the anus). The flatus is mainly composed of odorless gases. However, bacterial decomposition of food in the intestine contributes to the odor of the flatus. For example, a rotten-egg odor in the flatus is caused by the hydrogen sulfide gas produced by the action of intestinal bacteria.

Production of hydrogen sulfide in the bowels may also be enhanced by the action of foreign bacteria, parasites and yeasts. Consumption of foods with high sulfur content (such as meat, eggs, beer, and cabbage) causes increased production of hydrogen sulfide. Conditions such as irritable bowel syndrome, bowel obstruction, gastroparesis, and food intolerance are also associated with increased production of hydrogen sulfide.

Other causes of offensive putrid odor in flatus include food poisoning, pseudomembranous colitis, ulcerative colitis, Crohn’s disease, and chronic gut infections. These conditions result in flatus that has putrid odors like that of fish, dead animals, or rotting garbage.

Read more on excessive stomach gas.

Causes of Bloating and Gas

Gas accumulation and bloating can be caused by a variety of conditions that affect multiple regions of the gastrointestinal tract.


Aerophagia refers to involuntary or voluntary swallowing of air that may occur during eating, drinking, smoking, and anxiety. This excess air gets trapped within the esophagus and is expelled through belching. Gas that reaches the lower gastrointestinal tract gets expelled as flatus. Aerophagia is not a common cause of bloating. However, it can contribute to flatulence.

Consumption of certain food types

Consumption of certain foods such as carbonated beverages, beans, cabbage, alcohol, sweets, oats, bread, rice, and potatoes can cause increased gas production via the action of intestinal bacteria. Certain medications such as laxatives, antibiotics, and painkillers can also cause increased gas and bloating.

Helicobacter pylori infection

Stomach infection by the bacteria, Helicobacter pylori, contributes to diseases such as gastritis, peptic ulcer, and gastrointestinal reflux disease (abbreviated as GERD). Gas accumulation, belching, flatulence and bloating are common signs and symptoms of these conditions.

Dumping syndrome

Dumping syndrome is characterized by rapid passage of stomach contents into the intestine. This syndrome is caused by conditions such as gastric bypass surgery, diabetic neuropathy, damaged pylorus and Zollinger-Ellison syndrome.

Decreased gut motility

Decreased gut motility gives more time for the intestinal bacteria to act on the food and wastes in the gut. This causes increased gas accumulation and bloating. Causes of decreased gut motility include anorexia nervosa, bowel obstructions, disorders of the nerves and smooth muscles of the gut, and certain medications.

Pancreatic insufficiency

Decrease in the level of pancreatic enzymes in the small intestine can be caused by various conditions such as pancreatitis, gallstones, cystic fibrosis, pancreatic cancer, pancreatic infections, drugs, abdominal trauma and surgery. Bloating and flatulence occur during pancreatic insufficiency.

Biliary stasis

Biliary stasis refers to reduced bile production and secretion. Hepatitis, cirrhosis, gallstones, gallbladder cancer, cholecystitis, and cholecystectomy are some causes of biliary stasis.

Food poisoning

Consumption of food that is contaminated with pathogenic bacteria, viruses, and parasites results in food poisoning.

Small intestinal bacterial overgrowth

Most of the gut bacteria reside in the large intestine. An overgrowth of bacteria within the small intestine can occur in various conditions such as diabetes, thyroid disorders, anorexia nervosa, intestinal obstruction, pancreatitis, slow gut motility and formation of diverticuli. An overgrowth of natural flora in the small intestine is referred to as small intestinal bacterial overgrowth (abbreviated as SIBO).

Intestinal malabsorption

Inability to digest and absorb certain components of food (such as fructose and sorbitol) can also cause bloating and gas accumulation.

Lactose intolerance

Lactose intolerance is a common condition in which a person is unable to digest the lactose sugar present in milk and dairy products. Gas accumulation and bloating are common features of this condition.

Celiac disease

Celiac disease is characterized by an inability to absorb the gluten protein present in wheat, rye, oats, barley and some starchy foods.

Intestinal obstruction

A partial or complete blockage in the small or the large intestine also contributes to gas accumulation and bloating.

Short bowel syndrome

Surgical removal of a part of the small intestine can result in a malabsorption disorder known as the short bowel syndrome.

Irritable bowel syndrome

Irritable bowel syndrome is a functional disorder that affects bowel movements and causes flatulence and bloating upon consumption of certain trigger foods.


Constipation is characterized by a difficulty in passing stools. The backed up stool in the gut can cause gas accumulation and bloating.

Pseudomembranous colitis

Pseudomembranous colitis refers to an inflammation of the colon that is caused by an overgrowth of the bacteria, Clostridium difficile. This condition is also referred to as antibiotic-associated colitis.

Diverticulosis and diverticulitis

The term “diverticuli” refers to small outpouches that may grow from the walls of the gastrointestinal tract. Inflammation of the diverticuli is referred to as diverticulitis.

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