Swollen Stomach (Bloat) – Common Causes

The term ‘swollen stomach’ is often used to describe generalized abdominal distension or bloating. However, it may also indicate swelling in only one quadrant of the abdomen. The general approach to abdominal bloating is to consider the 5 F’s which are :

  • Flatus
  • Fat
  • Fluid
  • Feces
  • Fetus

Common Causes of Swollen Stomach


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.

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