Still bloated after a normal colonoscopy and blood tests?
The short answer
A normal colonoscopy and normal blood tests make serious bowel disease much less likely, though they don't examine every organ, which is why the baseline below matters. They also don't explain your bloating, and "go low-FODMAP and live with it" is not the only option left.
Bloating is a symptom, not a diagnosis. In my clinic, persistent bloating almost always falls into one or more of four recognisable types, each with its own test and its own treatment. The aim is to work out which type you are, rather than trying treatments at random.
The four types are Backed-up, Balloon belly, Fermenter and Slow stomach. Most people recognise themselves in one or two within a minute.
First, the baseline
Before sorting bloating into types, serious causes need to be excluded. Most people reading this have already had:
Colonoscopy (and often gastroscopy), to exclude bowel cancer, inflammation and other structural disease.
Coeliac serology, a blood test that is recommended for anyone with persistent bloating [1].
Pelvic ultrasound in women, particularly with new, persistent bloating after 50, to exclude an ovarian cause.
If you haven't had these and have red flags (weight loss, bleeding, anaemia, a change in bowel habit later in life, or a family history of bowel or ovarian cancer), start there with your GP. If you have had them, and you're still bloated, read on.
The four types of bloating
Type | You might be this type if… | What we check | What helps |
1. Backed-up | Bloating builds through the day and eases after a good bowel motion, even if you think your bowels are "normal" | Abdominal X-ray, anorectal manometry, transit study; pelvic ultrasound in women | Laxatives or prokinetics; pelvic floor biofeedback |
2. Balloon belly | Flat in the morning, looks pregnant by evening, yet scans show little extra gas | Clinical pattern; tests to exclude the other types | Diaphragmatic breathing and biofeedback; low-dose neuromodulators |
3. Fermenter | Gas, burping or bloating within a few hours of carbohydrate or high-FODMAP foods | SIBO and IMO breath tests; lactose and fructose breath tests | Targeted antibiotics; dietitian-led low-FODMAP with reintroduction |
4. Slow stomach | Full after small meals, nausea, bloating high in the upper abdomen | Gastric emptying study; medication review | Prokinetics; smaller, more frequent meals |
Most people are one or two types. The overlaps are explained further down.
Type 1: Backed-up
This is the most common type I see, and the most often missed, because many people in this group say their bowels are normal.
A daily bowel motion doesn't always mean the bowel is emptying fully. I regularly see people who describe "normal" stools whose abdominal X-ray shows a heavily loaded colon. Faecal loading on X-ray is a supporting finding, not proof of constipation: it varies, and it doesn't always match symptoms. Read alongside your history and examination, though, it often changes the conversation.
What we check
Abdominal X-ray to look for faecal loading, as one piece of the picture.
Anorectal manometry, when emptying feels incomplete or needs straining. It looks for pelvic floor dyssynergia, where the muscles tighten instead of relaxing during a bowel motion. The AGA recommends it for bloating linked to constipation [1].
Colonic transit study, in selected cases that don't respond to treatment [1].
Pelvic ultrasound in women, if not already done.
What helps
Treating constipation properly often relieves bloating, and the AGA recommends constipation medications for bloating when constipation is present [1]. That may mean an osmotic laxative, a prokinetic such as prucalopride, or a secretagogue. When the pelvic floor is the problem, biofeedback retrains it [1].
Type 2: Balloon belly
If your stomach is flat in the morning and you look several months pregnant by evening, the cause is often not extra gas. It's how your abdominal muscles respond to normal gas.
Normally, when the gut fills after a meal, the diaphragm relaxes upward and the abdominal wall tightens to hold everything in. In people with visible distension, this reflex runs backwards: the diaphragm contracts downward and the abdominal wall relaxes, pushing the belly out. This is called abdominophrenic dyssynergia (APD), and it has been shown in measured studies of muscle activity [2, 3].
The trigger is usually visceral hypersensitivity: a gut that senses ordinary amounts of gas as uncomfortable, setting off the abnormal reflex.
What we check
APD is a clinical diagnosis. The pattern is typical, and tests for the other three types are usually normal or only partly explain the symptoms.
What helps
Because APD is a reflex, it can be retrained. In a 2024 randomised trial, biofeedback that taught patients to control the diaphragm reduced distension scores by about two-thirds, with no benefit from placebo [4]. The AGA recommends diaphragmatic breathing and low-dose neuromodulators, which turn down gut sensitivity [1]. Gut-directed hypnotherapy and CBT also help [1].
Type 3: Fermenter
If bloating, gas or burping follows carbohydrate or high-FODMAP foods within hours, the issue is usually fermentation: bacteria breaking down food in a part of the gut, or in amounts, that they shouldn't.
There are three main causes:
Carbohydrate malabsorption, such as lactose or fructose that isn't absorbed and reaches bacteria further down [1].
SIBO (small intestinal bacterial overgrowth), where hydrogen-producing bacteria grow in the small bowel [5].
IMO (intestinal methanogen overgrowth), the newer name for methane-positive breath tests. Methane slows gut transit, so IMO tends to cause bloating with constipation [5, 7].
What we check
Breath tests measure the hydrogen and methane produced after a test sugar. They are used selectively, in people whose symptoms point this way, not as a screen for everyone [1, 5]. They also have real limitations: results can be affected by fast transit, recent antibiotics and test preparation, and no breath test is a perfect measure of small bowel bacteria [5]. I use them to support a diagnosis, read together with your symptoms, not as a stand-alone verdict.
What helps
Targeted antibiotics. Rifaximin is minimally absorbed and stays largely in the gut. Its strongest evidence is in IBS without constipation: in two large randomised trials, it relieved bloating in about 40% of patients vs 30% on placebo [6]. Those trials didn't require a positive breath test. Evidence for treating breath-test-confirmed SIBO comes from smaller studies, reviewed in the ACG guideline [5]. IMO usually needs a combination treatment. In Australia, rifaximin is not PBS-subsidised for this use.
A dietitian-led low-FODMAP diet, with structured reintroduction rather than long-term restriction [1].
If you've already tried low-FODMAP without lasting relief, that doesn't rule out this type. It often means the underlying fermentation hasn't been tested or treated.
Type 4: Slow stomach
This type is about the upper gut. You feel full after a small meal, the bloating sits high under the ribs, and nausea is common.
The stomach may empty slowly, or may not relax properly to accommodate food. Causes include diabetes, a previous viral illness and medications. GLP-1 medicines such as semaglutide and tirzepatide slow stomach emptying and are now a common cause of new bloating. Opioid painkillers do the same.
What we check
A gastric emptying study, when nausea or vomiting is part of the picture. The AGA advises against ordering it routinely for bloating alone [1, 8].
A medication review, which is quick, free and often the most useful step.
What helps
Smaller, more frequent and lower-fat meals; prokinetic medication where emptying is confirmed slow [8]; and, where possible, adjusting the medicine responsible.
Most people are two types
The types overlap, and the overlaps explain why single treatments often only half-work.
Fermenter + Backed-up. Methane from IMO slows the bowel [7], and a slow bowel gives bacteria more time to ferment. Treating only one side tends to bring the bloating back.
Backed-up + Balloon belly. A loaded colon stretches a sensitive gut, which can trigger the abnormal abdominal wall reflex.
Slow stomach + Balloon belly. The same reflex has been measured after meals in people with functional dyspepsia [3].
This is why I assess all four before choosing treatment. Finding your combination is usually what turns years of trial and error into a plan that works.
Getting assessed
I see patients with persistent bloating after normal investigations at the Mater Hospital, North Sydney, and Northern Beaches Hospital, Frenchs Forest. A GP referral is required. Bring your colonoscopy report, blood results and any previous breath tests.
General information only, not a substitute for individual medical advice.
Related reading
References
Moshiree B, Drossman D, Shaukat A. AGA clinical practice update on evaluation and management of belching, abdominal bloating, and distention. Gastroenterology. 2023;165(3):791-800. doi:10.1053/j.gastro.2023.04.039
Villoria A, Azpiroz F, Burri E, et al. Abdomino-phrenic dyssynergia in patients with abdominal bloating and distension. Am J Gastroenterol. 2011;106(5):815-819. doi:10.1038/ajg.2010.408
Burri E, Barba E, Huaman JW, et al. Mechanisms of postprandial abdominal bloating and distension in functional dyspepsia. Gut. 2014;63(3):395-400. doi:10.1136/gutjnl-2013-304574
Barba E, Livovsky DM, Accarino A, Azpiroz F. Thoracoabdominal wall motion-guided biofeedback treatment of abdominal distention: a randomized placebo-controlled trial. Gastroenterology. 2024;167(3):538-546. doi:10.1053/j.gastro.2024.03.005
Pimentel M, Saad RJ, Long MD, Rao SSC. ACG clinical guideline: small intestinal bacterial overgrowth. Am J Gastroenterol. 2020;115(2):165-178. doi:10.14309/ajg.0000000000000501
Pimentel M, Lembo A, Chey WD, et al. Rifaximin therapy for patients with irritable bowel syndrome without constipation. N Engl J Med. 2011;364(1):22-32. doi:10.1056/NEJMoa1004409
Pimentel M, Lin HC, Enayati P, et al. Methane, a gas produced by enteric bacteria, slows intestinal transit and augments small intestinal contractile activity. Am J Physiol Gastrointest Liver Physiol. 2006;290(6):G1089-1095. doi:10.1152/ajpgi.00574.2004
Camilleri M, Kuo B, Nguyen L, et al. ACG clinical guideline: gastroparesis. Am J Gastroenterol. 2022;117(8):1197-1220. doi:10.14309/ajg.0000000000001874
References retrieved via PubMed.
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