Abdominal Bloating (Swollen Stomach) Causes and Conditions

What is abdominal bloating?

Abdominal bloating is any enlargement of the abdomen (distension) or fullness sensation in the abdomen with/without distension. When there is visible enlargement then this abdominal distension (enlargement of the abdomen) is most commonly due to one of the following :

  • Fat
  • Fluid
  • Feces
  • Flatus
  • Fetus

Bloating that is transient and may come on suddenly and pass just as quickly is more likely due to gas accumulation within the gut. While fluid may also cause bloating, often the term ‘bloat’ is associated with gas while abdominal swelling is attributed to fluid accumulation (ascites).


In this case, the abdominal distention is due to gas in the gastrointestinal tract. Gas in the gut may be due to :

  • Gas from swallowing of air (aerophagia) – this gas contains mainly oxygen and nitrogen and is more likely to be found in the esophagus, stomach and first part of the small intestine.
  • Gas from bacterial action on food – this as contains mainly carbon dioxide, methane and hydrogen and is more likely to be found in the small intestine and large intestine.
  • Gas that diffuses from the blood into the gastrointestinal tract – mainly nitrogen.

At any time, the gut contains less than 200 ml of gas because the gas is usually passed out as a belch, flatus or certain elements like hydrogen are even absorbed into the blood and passed out through the lungs. However, the total movement of gas in and out of the gut can be between 7 to 10 liters per day. Only about 600 to 700ml of this gas is passed out as flatus (average 15 expulsions per day).

Apart from abdominal bloating, excessive gastrointestinal gas may be evident as :

Other articles related to gas in the gastrointestinal tract :


This is related to a gain in body weight (overweight or obesity) due to an increase in body fat percentage. The normal body fat percentage is approximately 15% to 20% in men and 22% to 28% in women although this may be lower in an athlete.

The fat accumulation may be throughout the body and is accentuated in certain areas like :

  • Men – abdomen and areas above (android or apple-shape)
  • Women – abdomen and areas below like the hips, thighs, buttock (gynoid or pear shape)

An increase in body fat is a result of an excessive intake of calories (food, overeating) compared to the calories used (physical activity).

Some of the other causes that need to be considered include :

  • Hypothyroidism
  • Cushing’s syndrome and Cushing’s disease
  • Eating disorders
  • Polycystic ovary syndrome (PCOS)
  • Diabetes mellitus although weight loss is a more common feature.
  • Drugs


This fluid accumulation within the abdomen can occur in the peritoneal cavity which is a potential space between the parietal peritoneum on the abdominal wall and visceral peritoneum that surrounds the abdominal organs and other structures. The peritoneal cavity extends downwards (inferiorly) into the pelvic cavity.

Normally there is little or no intraperitoneal fluid (fluid within the peritoneal cavity) in men but there can be as much as 20ml (milliliters) of fluid in women. This may change during the course of the menstrual cycle and may be more evident in the lower abdomen or pelvic cavity.

Pathological fluid accumulation (edema) in the abdominal cavity  is known as ascites. Some of the causes of abdominal bloating includes :

  • Cirrhosis
  • Pancreatitis
  • Infection
  • Lymphatic obstruction
  • Kidney failure
  • Heart failure
  • Malignancy – cancer of the digestive organs or ovary.

Intra-abdominal bleeding should also be considered if there are signs of shock.


Intestinal chyme is the watery intestinal contents (digested food and water) that enters the colon and gradually passes through the colon. The colon is responsible for absorption of residual nutrients and water from the intestinal chyme as well as storage of the contents and feces. As the intestinal chyme passes through the colon, it goes through changes in the consistency :

  • fluid upon entering the ascending colon
  • semi-fluid as it approaches the right colic flexure (hepatic flexure)
  • mushy in the transverse colon
  • consistency between mushy and semi-solid as it approaches the left colic flexure (splenic flexure)
  • semi-solid in the descending colon
  • solid in the sigmoid colon

Any obstruction within the colon, impairment of the movement of colonic contents or failure to pass feces regularly will cause a build up within the colon. Causes include :

  • Constipation – most common cause
  • Paralytic ileus
  • Tumor
  • Impacted feces
  • Adhesions
  • Intussusception
  • Volvulus
  • Melanosis coli and laxative misuse syndrome
  • Hirschsprung’s disease
  • Acquired megacolon


Any woman who is of a reproductive age should be considered to be pregnant unless proven otherwise, especially if there is reporting of a missed period (amenorrhea), swelling and/or tenderness of the breast and episodes of nausea and vomiting particularly in the morning (‘morning sickness’). Abdominal distension is a normal part of pregnancy. The time when the distension becomes obvious varies among women (anywhere between 8 weeks to 16 weeks). It can be as early as within the first 4 weeks or as late as 20 weeks.

Causes of Abdominal Gas Bloating

Abdominal bloating refers to a clearly visible distension of the abdomen. This is in contrast to the feeling of being bloated which is a sensation of fullness in the abdomen, usually in the upper parts of the abdomen.

Gas production within the alimentary tract is a normal occurrence. It arises as a result of gas being produced during chemical digestion, the byproduct of bacteria consuming nutrients within the gut and decomposition of waste. Two very common and non-pathological causes of gas bloating is the swallowing of air, which is known as aerophagia, and the consumption of carbonated beverages like fizzy soda, beer and sparkling wine.

The gut contains less than 200 milliliters of gas although anywhere between 1 to 2 liters of gas is passed out in a day. In most cases associated with abdominal gas bloating, excessive belching or flatulence, the volume of gastrointestinal gas is not larger than normal.

Although rare, gas outside the bowels but within the abdominal cavity is known as pneumoperitoneum. It is a result of perforation of the stomach or intestines, as gas escapes from the gut into the peritoneal cavity. This is usually very painful and considered as a medical emergency as microorganisms from the gut will enter the sterile peritoneal cavity and result in a serious, even life-threatening, infection (peritonitis).

Signs and Symptoms of Abdominal Gas Bloating

Abdominal bloating as a result of gas accumulation within the gut may result in a number of signs and symptoms apart from the visible enlargement of the abdomen. This includes :

Changes in bowel movement, like loose stool to diarrhea or constipation, and a general sense of feeling unwell or lethargic may also be present. These signs and symptoms may occur independently as concomitant features of the cause or may be a result of gas accumulation within the gut.

The enlargement is usually generalized throughout the abdomen as a result of gas accumulation. Rarely pockets of gas are trapped in one section of the bowel, usually the colon, where it will cause a visible and palpable bulge in one quadrant of the abdomen.

Conditions that Cause Abdominal Gas Bloating

A number of conditions may result in abdominal bloating due to gas accumulation within the gut. These causes are discussed further under :

Irritable bowel syndrome (IBS)

Abdominal bloating is one of the features of IBS, although the gas volume within the bowel does not appear to be greater than normal. Gas bloating may occur very suddenly and can severe to the extent that the abdominal distension can become painful due to stretching of the abdominal wall and even alter the usual clothing sizes.


Some of the following infectious conditions may result in abdominal bloating due to gas accumulation.

Food Intolerance and Malabsorption

The inability to digest or absorb the following substances may provide additional nutrition for the the naturally occurring intestinal bacteria to consume. Gas is often produced as a byproduct by these bacteria. In addition, the decomposition of these nutrients will also contribute to gas accumulation.


The ability to digest certain or all foods may be compromised as a result of inactivation of digestive enzymes or a lack of these enzymes. The control mechanisms involving the digestive hormones or nerve supply to the gut may also be compromised.  This is discussed further under Digestive Problems.

Gastrointestinal Motility

The rapid or slow transit of food and chyme through the gastrointestinal tract may impair both digestion and absorption. This may be due to weak muscle activity or lack of coordination in peristalsis, obstructions or resection or strangulation of the bowels.


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