Functional Bloating

Functional bloating is recurrent bloating (a subjective sensation of trapped gas, pressure or fullness in the abdomen) and distension (visible, measurable increase in abdominal girth). It is present at least 1 day per week for the last 3 months, with onset at least 6 months before diagnosis.

Diagnosis requires the absence of irritable bowel syndrome, functional constipation, functional diarrhoea, or functional dyspepsia criteria, and no identifiable structural or biochemical cause.

• It affects about 10 to 30% of the general population, and women are affected up to twice as often as men. Peak age is 20 to 50 years. It is a leading reason for primary care and gastroenterology referral, and impairs quality of life and productivity.
• Mechanisms (multifactorial):
  • Visceral hypersensitivity: a heightened perception of normal volumes of intestinal gas and distension.
  • Abdominophrenic dyssynergia: a paradoxical response to gas or food in which the diaphragm contracts (descends) and the abdominal wall muscles relax, instead of the normal accommodation, leading to protrusion of the abdomen (distension) without an increase in gas volume.
  • Altered gut motility, slow transit of gas, and abnormal gas handling.
  • Gut microbiota changes and fermentation of poorly absorbed carbohydrates (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) producing gas, and small intestinal bacterial overgrowth in some patients.
  • Altered central processing of pain, with anxiety, depression, and stress as modulators.
  • Constipation and delayed colonic transit, which increase the gas load.
• Triggers: meals (especially high in fermentable carbohydrates, fat, fizzy drinks, legumes, onions, garlic, wheat, artificial sweeteners), menstruation (cyclical bloating in 70% of women), stress, swallowed air (aerophagia, chewing gum, rapid eating), and weight gain.
• Distension is typically progressive during the day and worst by the evening, settling overnight when lying flat.
• Many patients (about 90% of those with irritable bowel syndrome and 50% of those with functional constipation) have bloating, and functional bloating as a stand alone diagnosis applies when the other criteria are not met.

• Recurrent abdominal bloating and visible distension, worse after meals and later in the day, with relief overnight, and sometimes with belching, flatulence, borborygmi, abdominal discomfort, early satiety and fullness. The patient may need to loosen clothes.
• No alarm features: no weight loss, bleeding, anaemia, nocturnal symptoms, or progressive pain.
• Examination: the abdomen is soft, with no mass, tenderness or ascites. The abdomen may be visibly distended, and distension can disappear under general anaesthesia or when lying down, supporting abdominophrenic dyssynergia. Tympany may be increased.
• Differential diagnosis: irritable bowel syndrome, functional constipation, functional dyspepsia, coeliac disease, lactose and fructose intolerance, small intestinal bacterial overgrowth, gastroparesis, pancreatic exocrine insufficiency, bile acid malabsorption, giardiasis, inflammatory bowel disease.
• Further differentials: ascites (liver disease, heart failure, malignancy), ovarian cancer, other pelvic masses, pregnancy, hypothyroidism, medicines (GLP-1 receptor agonists, opioids, anticholinergics, calcium channel blockers, acarbose, metformin, iron), weight gain, and intestinal pseudo obstruction.
• Red flags: new persistent bloating in women over 50 years (consider ovarian cancer), weight loss, rectal bleeding, iron deficiency anaemia, change in bowel habit in those over 50 years, nocturnal symptoms.
• Further red flags: vomiting, progressive distension with ascites, abdominal mass, family history of colorectal, ovarian or coeliac disease, fever, jaundice, and severe pain.
• Complications: poor quality of life, dietary restriction and nutritional deficiency, avoidance of social activities, anxiety, depression, and unnecessary investigation or surgery.

• Clinical diagnosis based on symptoms after exclusion of organic disease in patients with alarm features. Document the pattern (timing, relationship to meals and menstruation, distension measurement), diet, medicines, bowel habit, and psychological factors using a symptom diary (2 weeks).
• Initial tests in patients with persistent symptoms and no alarm features: full blood count, ferritin, C-reactive protein, coeliac serology (tissue transglutaminase IgA with total IgA), thyroid function tests, glucose or HbA1c, and faecal calprotectin when diarrhoea is present. Pregnancy test where appropriate.
• Women over 50 years with persistent bloating (more than 12 times a month): serum CA125 and pelvic ultrasound to exclude ovarian cancer.
• Further tests, directed by the findings:
  • Hydrogen and methane breath tests for lactose and fructose malabsorption, and small intestinal bacterial overgrowth, with careful interpretation (poor specificity).
  • Faecal elastase for pancreatic insufficiency, and stool tests for Giardia.
  • Abdominal ultrasound for ascites, liver disease and masses, CT for suspected structural disease, and gastric emptying study when upper gastrointestinal symptoms or vomiting predominate.
  • Upper endoscopy with duodenal biopsies for coeliac disease, and colonoscopy for red flags.
  • Anorectal physiology and colonic transit studies for constipation with bloating.
  • Abdominal circumference or abdominal wall electromyography, in specialist units, to demonstrate abdominophrenic dyssynergia.
• Screen for anxiety, depression and somatic symptom disorder.

• Explain the condition, that the findings are not dangerous, and that distension reflects abnormal gut and abdominal wall responses rather than excess gas. Reassurance reduces anxiety and consultations.
• Lifestyle and dietary measures:
  • Regular meals, eating slowly, chewing well, small portions, avoiding gum, hard sweets, fizzy drinks, drinking through a straw, and smoking, to reduce swallowed air.
  • A food and symptom diary to identify triggers.
  • Increase soluble fibre (ispaghula husk 3.5 g once daily, increased slowly to 7 g twice daily) and avoid insoluble bran, which worsens bloating. Physical exercise (30 minutes of walking daily) improves gas transit.
  • A low fermentable carbohydrate diet (restriction of fermentable oligosaccharides, disaccharides, monosaccharides and polyols) for 4 to 6 weeks under a dietitian's supervision, followed by a structured reintroduction to find personal triggers and then a long term, least restrictive diet. About 50 to 70% of patients respond. Avoid prolonged strict restriction because of the risk to the microbiota and nutrition.
  • Reduce sorbitol, mannitol and xylitol in sugar free products, and review lactose, fructose and legume intake.
• Medicines (modest, short term benefit):
  • Peppermint oil, enteric coated, 0.2 mL (181 to 187 mg) orally 3 times daily before meals for 4 to 8 weeks. Avoid in reflux, hiatus hernia, and gall stones.
  • Simethicone 40 to 125 mg orally after meals and at bedtime (up to 500 mg per day), or activated dimeticone, with little evidence of benefit beyond placebo, but with a good safety profile.
  • Antispasmodics for pain: hyoscine butylbromide 10 to 20 mg orally 3 to 4 times daily, mebeverine 135 mg orally 3 times daily before meals, or alverine citrate 60 to 120 mg orally 3 times daily. Avoid in glaucoma, prostatic enlargement, and ileus.
  • Probiotics: a 4 week course of a multi strain product or Bifidobacterium or Lactobacillus species, stopping if there is no benefit.
  • Rifaximin 550 mg orally 3 times daily for 14 days, for suspected small intestinal bacterial overgrowth or bloating with diarrhoea, with a response in about 40 to 50% (up to 2 retreatments).
  • Constipation: macrogol 1 to 2 sachets daily, or prucalopride 2 mg daily (1 mg in those over 65 years).
  • For bloating with constipation: linaclotide 290 micrograms orally once daily on an empty stomach, 30 minutes before the first meal of the day (diarrhoea is the main adverse effect).
  • Neuromodulators for persistent symptoms with visceral hypersensitivity: amitriptyline 10 mg orally at night, increased by 10 mg every 1 to 2 weeks to 25 to 50 mg, or nortriptyline 10 to 25 mg at night, for at least 3 months. Review anticholinergic effects, constipation and drowsiness. Duloxetine 30 to 60 mg daily, or sertraline in comorbid anxiety, are alternatives.
  • Avoid charcoal, bulk agents without evidence, repeated antibiotics, and opioids.
• Abdominophrenic dyssynergia: biofeedback assisted abdominal wall retraining by a physiotherapist (diaphragmatic breathing with relaxation of the diaphragm and active tone in the abdominal wall, 4 to 6 sessions), which reduces distension in about 60 to 70% of those with confirmed dyssynergia.
• Psychological therapy: cognitive behavioural therapy and gut directed hypnotherapy (6 to 12 sessions), mindfulness, and stress management.
• Treat associated conditions: coeliac disease (gluten free diet), lactose intolerance (lactose restriction), pancreatic insufficiency (enzyme replacement), small intestinal bacterial overgrowth, constipation, aerophagia (speech therapy and behavioural therapy).
• Treat gastroparesis with dietary changes, metoclopramide 5 to 10 mg orally 3 times daily before meals for a maximum of 5 days at a time, or domperidone 10 mg 3 times daily, under specialist care.
• Special groups:
  • Pregnancy: bloating is common (progesterone effect), so use diet, fibre, exercise, and macrogol or lactulose for constipation. Simethicone and peppermint oil have limited data, and are avoided in first trimester unless needed.
  • Children and adolescents: reassurance, dietary history, exclusion of constipation, coeliac disease and lactose intolerance, and behavioural therapy. Avoid restrictive diets without supervision.
  • Elderly: investigate more readily for malignancy and medicine effects, and avoid anticholinergic drugs.
  • Women with cyclical bloating: advise on timing, use of exercise, salt and caffeine reduction, and review hormonal contraception.
  • Renal impairment: avoid magnesium containing laxatives.
• Follow up: review at 4 to 8 weeks to assess response, and after dietary reintroduction. Refer to a gastroenterologist or dietitian for refractory symptoms, abnormal tests or red flags, and to gynaecology for suspected ovarian or pelvic disease.