Abdominal Bloating

Abdominal bloating is a symptom: a feeling of fullness, pressure, trapped gas or abdominal swelling, which may occur with or without visible distension.

It is among the commonest gastrointestinal complaints, affecting up to 20 to 30% of the general population and reported by up to 90% of patients with irritable bowel syndrome.

• Bloating is not synonymous with gas excess. Objective measurement shows that most patients have normal gas volumes, and the symptom arises from visceral hypersensitivity, abnormal abdominal wall and diaphragm reflexes, dysmotility, and altered microbiota. A normal adult passes about 600 to 700 mL of gas daily (a mean of 14 to 23 passages), and the stomach and bowel contain 100 to 200 mL.

• Gas sources: swallowed air (aerophagia, 70% of gas in the stomach), bacterial fermentation of undigested carbohydrate in the colon (hydrogen, methane, carbon dioxide), carbon dioxide from the reaction of acid and bicarbonate, and diffusion from blood.

• Causes (by category):

  • Gastrointestinal functional: irritable bowel syndrome, functional dyspepsia, functional constipation, functional bloating, and aerophagia.

  • Dietary: fermentable carbohydrates (onions, garlic, legumes, wheat, apples), fructose, lactose, sorbitol and other sugar alcohols, fizzy drinks, cruciferous vegetables, and high fibre or high fat meals.

  • Malabsorption and bacterial: coeliac disease, lactose intolerance, small intestinal bacterial overgrowth, bile acid malabsorption, pancreatic exocrine insufficiency, giardiasis, and short bowel.

  • Motility: constipation, gastroparesis, and chronic intestinal pseudo obstruction.

  • Structural and organic: bowel obstruction, adhesions, volvulus, Crohn disease strictures, colorectal cancer, ovarian cancer, ascites (cirrhosis, heart failure, nephrotic syndrome, peritoneal malignancy, tuberculosis), pancreatic disease, gallbladder disease, and pelvic masses (fibroids, ovarian cysts).

  • Gynaecological and endocrine: premenstrual and menstrual bloating, pregnancy, menopause, endometriosis, hypothyroidism, and polycystic ovary syndrome.

  • Medicines: GLP-1 receptor agonists, opioids, anticholinergics, calcium channel blockers, iron, metformin, acarbose, orlistat, fibre supplements, laxatives, antidepressants, and levodopa.

  • Others: weight gain, fluid retention, hernia, and anxiety.

• It is more common in women (about 2 times) and in people with anxiety, depression and a history of abuse. Many patients have more than one contributing cause.

• A sense of fullness and swelling of the abdomen that often builds through the day, and may be worse after meals, with visible distension, belching, flatulence, borborygmi, and abdominal discomfort. Clothes become tight, and relief often follows passage of gas or stool or lying down overnight.
• Features suggesting the cause:
  • Postprandial bloating with early satiety, nausea or vomiting, epigastric pain: functional dyspepsia, gastroparesis.
  • Bloating with altered stools, and pain relieved by defecation: irritable bowel syndrome.
  • Bloating with infrequent hard stools: constipation.
  • Bloating after dairy products, fruit, sweeteners or wheat, with watery stools and flatulence: carbohydrate intolerance.
  • Bloating with diarrhoea, weight loss, anaemia, steatorrhoea, mouth ulcers or an itchy rash: coeliac disease.
  • Bloating with diarrhoea after antibiotics, surgery, or with diabetes or scleroderma: small intestinal bacterial overgrowth.
  • Excess belching and swallowing of air, with visible air swallowing: aerophagia.
  • Persistent bloating with abdominal swelling, weight loss, early satiety, urinary frequency, pelvic pain and a woman over 50 years: ovarian cancer.
  • Progressive distension with oedema, jaundice, shortness of breath, and a fluid thrill or shifting dullness: ascites.
  • Colicky pain, vomiting, constipation and absolute distension: bowel obstruction.
• Examination: weight, nutritional state, pallor, jaundice, oedema, thyroid, abdominal distension and tenderness, masses, ascites (shifting dullness, fluid thrill), hernias, bowel sounds, and digital rectal examination.
• Differential diagnosis: irritable bowel syndrome, functional dyspepsia, constipation, aerophagia, dietary fermentable carbohydrates, lactose and fructose intolerance, coeliac disease, small intestinal bacterial overgrowth, pancreatic insufficiency, gastroparesis, ascites, intestinal obstruction, ovarian cancer, pelvic masses, and medicine effects.
• Red flags: unintentional weight loss, rectal bleeding, iron deficiency anaemia, persistent vomiting, dysphagia, a palpable mass, new onset bloating persisting beyond 3 to 4 weeks in a woman over 50 years, ascites, jaundice, family history of ovarian, colorectal or coeliac disease, nocturnal symptoms, fever, severe or progressive pain, and a change in bowel habit in patients over 50 years.
• Complications: poor quality of life, anxiety, dietary restriction, malnutrition from unnecessary exclusion diets, and delayed diagnosis of serious disease.

• Clinical assessment: duration, timing (post-meal, evening, premenstrual), measure of distension, food triggers, bowel habit (stool chart), medicines (including supplements and sweeteners), weight changes, menstrual and gynaecological history, family history, and psychological stress. Keep a 2 week symptom and food diary.
• Examination: general state and weight, abdomen (distension, tympany, shifting dullness, masses, tenderness, hernias), rectal examination, and pelvic examination when indicated.
• First line tests (patients with persistent symptoms): full blood count, ferritin, C-reactive protein, urea and electrolytes, liver tests, albumin, coeliac serology (tissue transglutaminase IgA with total IgA), thyroid function tests, glucose, and faecal calprotectin for diarrhoea. Pregnancy test in women of childbearing age.
• CA125 and pelvic ultrasound in women with persistent or frequent bloating (more than 12 days per month) who are over 50 years, and in younger women with other symptoms.
• Abdominal ultrasound or CT for suspected ascites, masses, organ disease, or obstruction. Abdominal X-ray for suspected obstruction or faecal loading.
• Hydrogen and methane breath tests for lactose and fructose malabsorption and small intestinal bacterial overgrowth, with attention to their limitations. Stool Giardia antigen, faecal elastase, and bile acid tests if diarrhoea is present.
• Endoscopy: upper endoscopy with duodenal biopsies (coeliac disease, giardiasis, dyspepsia), and colonoscopy when red flags are present. Gastric emptying scintigraphy for suspected gastroparesis.
• Anorectal tests for constipation with evacuation difficulty, and abdominal wall tests in specialist centres for abdominophrenic dyssynergia.

• Treat any identified cause, and explain the mechanism of bloating, which is often not caused by excess gas.
• Dietary and lifestyle measures for all patients:
  • Eat regular meals slowly in a calm setting, chew food well, and avoid gum, hard sweets, drinking through straws, smoking and carbonated drinks, to reduce swallowed air.
  • Identify triggers with a food diary, and reduce known culprits (beans, onions, garlic, wheat in large amounts, brassica vegetables, apples and pears, sugar free products with sorbitol and mannitol, dairy if lactose intolerant).
  • Increase soluble fibre gradually (ispaghula husk 3.5 g once daily, up to 7 g twice daily with plenty of water), and avoid sudden increases in insoluble fibre.
  • Regular physical activity (30 minutes daily), weight control, and avoidance of tight clothes.
  • A low fermentable carbohydrate diet for 4 to 6 weeks with dietitian support, then structured reintroduction. It helps 50 to 70% of those with irritable bowel syndrome.
  • Alpha galactosidase enzyme (300 to 600 galactose units with the first bite of beans and vegetables) reduces gas from legumes in some people.
• Symptomatic treatment:
  • Peppermint oil enteric coated capsules 0.2 mL 3 times daily before meals for 4 to 8 weeks.
  • Simethicone 40 to 125 mg orally after meals and at bedtime (maximum 500 mg per day), for short term relief, with limited evidence of benefit.
  • Antispasmodics for pain: hyoscine butylbromide 10 to 20 mg orally 3 to 4 times daily, mebeverine 135 mg 3 times daily before meals, or alverine citrate 60 to 120 mg 3 times daily.
  • Probiotics for 4 weeks (Bifidobacterium or Lactobacillus species), and stop if no benefit.
• Targeted treatment:
  • Constipation: macrogol 1 to 2 sachets daily, increasing fluids and activity, with senna 7.5 to 15 mg at night when needed. Prucalopride 2 mg once daily (1 mg in those over 65 years) or linaclotide 290 micrograms orally once daily for constipation predominant irritable bowel syndrome.
  • Coeliac disease: strict lifelong gluten free diet after confirmed diagnosis (never start before testing), with dietitian support and correction of deficiencies.
  • Lactose intolerance: reduce lactose, use lactose free products, or lactase enzyme 3000 to 9000 units with dairy.
  • Small intestinal bacterial overgrowth: rifaximin 550 mg orally 3 times daily for 14 days (or 400 mg 3 times daily for 10 days), or ciprofloxacin 500 mg 12 hourly for 7 days, or amoxicillin clavulanate 625 mg 8 hourly for 7 days, and treat the underlying cause (dysmotility, strictures, proton pump inhibitor use). Relapse is common.
  • Pancreatic exocrine insufficiency: pancreatic enzymes (lipase 40,000 to 50,000 units with main meals, 20,000 to 25,000 units with snacks).
  • Gastroparesis: small frequent low fat low fibre meals, glycaemic control in diabetes, metoclopramide 5 to 10 mg orally 3 times daily before meals for no more than 5 days at a time, or domperidone 10 mg orally 3 times daily before meals for the shortest time (check the QT interval), under specialist care.
  • Functional dyspepsia: omeprazole 20 mg daily for 4 to 8 weeks, with amitriptyline 10 mg at night (increasing to 25 to 50 mg) for refractory symptoms.
  • Aerophagia: behavioural and speech therapy, awareness training, diaphragmatic breathing, and treatment of anxiety.
  • Abdominophrenic dyssynergia: biofeedback abdominal wall retraining with a physiotherapist.
  • Medicine induced bloating: reduce the dose or change the medicine (for example, slow titration or a switch from a GLP-1 receptor agonist, review of opioids and anticholinergics).
  • Ascites: diagnostic paracentesis, treatment of the cause, and diuretics (spironolactone 100 mg and furosemide 40 mg orally once daily in the morning, adjusted every 3 to 5 days to a maximum of 400 mg and 160 mg).
  • Ovarian cancer and other malignancy: urgent specialist referral.
  • Premenstrual bloating: reduce salt and caffeine, exercise, and review hormonal contraception, with a diuretic only in selected cases.
• Neuromodulators and psychological therapy for persistent functional bloating: amitriptyline 10 mg orally at night increased to 25 to 50 mg, cognitive behavioural therapy and gut directed hypnotherapy for 6 to 12 sessions.
• Special groups:
  • Pregnancy: reassurance, small meals, fibre, fluids, and lactulose or macrogol for constipation. Avoid excessive laxatives and unproven remedies.
  • Children: assess for constipation, lactose and fructose intolerance, coeliac disease, and aerophagia. Avoid unsupervised exclusion diets.
  • Elderly: investigate for malignancy and medicine effects, avoid anticholinergics, and review for ascites, obstruction and heart failure.
  • Diabetes: consider gastroparesis and autonomic neuropathy, review metformin and acarbose.
  • Renal and hepatic impairment: avoid magnesium containing laxatives, and adjust drug doses.
• Follow up: review at 4 to 8 weeks after starting treatment. Refer to gastroenterology, gynaecology or dietetics for red flags, abnormal tests, or no improvement with initial measures.