IBS explained: how it's diagnosed and what actually helps

"It's probably just IBS." Plenty of women hear some version of that sentence and leave the appointment feeling brushed off. It can sound like a shrug, as if the doctor simply ran out of ideas.

In reality, irritable bowel syndrome is a specific diagnosis with defined criteria, a sensible testing strategy and treatments that have been studied in controlled trials. Knowing how it works makes it easier to get good care, and to notice when something else might be going on.

What IBS is

IBS belongs to a group called functional bowel disorders. Other members of the group include functional constipation, functional diarrhea and functional abdominal bloating or distention (Mearin et al., 2016). In these conditions, the problem lies in how the gut works and feels rather than in visible damage to it.

IBS is common. A meta-analysis of population surveys found that about 3.8% of adults met the stricter Rome IV criteria, and 9.2% met the older Rome III criteria. It was more common in women than in men, at 12.0% versus 8.6% (Oka et al., 2020).

How doctors diagnose it

IBS is diagnosed mainly from your symptoms, using the Rome IV criteria. In short, you need recurring abdominal pain, on average at least one day a week over the last three months, linked to at least two of the following (Mearin et al., 2016):

• The pain is related to having a bowel movement
• It comes with a change in how often you go
• It comes with a change in how your stool looks

The symptoms also need to have started at least six months before diagnosis. Bloating is very common in IBS, but frequent bloating without this kind of pain may fit a different functional diagnosis.

Doctors then sort IBS by your main stool pattern: IBS with constipation, IBS with diarrhea, mixed, or unclassified. This matters because treatments differ by subtype. Among people with IBS, women are more likely than men to have the constipation-predominant type (Lovell and Ford, 2012).

Which tests make sense

For years, IBS was treated as a diagnosis of exclusion, reached only after a long list of tests came back normal. The American College of Gastroenterology's 2021 guideline suggests a different approach: a positive diagnostic strategy based on symptoms, which gets people to appropriate treatment sooner (Lacy et al., 2021).

That doesn't mean no testing. For people with IBS and diarrhea symptoms, the guideline suggests a blood test for celiac disease and a stool test called fecal calprotectin to help rule out inflammatory bowel disease (Lacy et al., 2021). Your doctor will also look for red flags, and a colonoscopy may still be needed if you're due for screening or have warning signs.

Why it can show up in midlife

IBS can start at any age, and there's rarely a single cause. One well-documented trigger is a bout of gastroenteritis. In a meta-analysis of 45 studies including 21,421 people who had an intestinal infection, 10.1% had IBS 12 months later. Women had about twice the odds of developing it (Klem et al., 2017).

Changes in hormones and gut sensitivity may also play a part for women in their 40s. We've covered what shifts in the gut after 40 in more detail. What matters most for diagnosis is timing: symptoms that are brand new after 50, or that come with red flags, deserve a closer look before anyone settles on IBS.

Treatments with the best evidence

The ACG guideline graded the evidence for many common treatments. Some highlights (Lacy et al., 2021):

• A limited low-FODMAP trial. Recommended to improve overall symptoms, ideally as a short-term test followed by reintroducing foods. Inulin is one of the most common FODMAPs in gut health products. Here's why it can backfire.
• Soluble fiber. Recommended for overall IBS symptoms, while insoluble fiber, such as wheat bran, is not.
• Gut-directed psychotherapy. Approaches such as cognitive behavioral therapy and gut-directed hypnotherapy are suggested for overall symptoms. That isn't because IBS is "in your head," but because the gut and brain constantly communicate.
• Prescription options by subtype. For IBS with constipation, the guideline recommends two classes of prescription drugs, chloride channel activators and guanylate cyclase activators. For IBS with diarrhea, it recommends the antibiotic rifaximin.

The guideline doesn't recommend probiotics for overall IBS symptoms, because the evidence is still weak and inconsistent. If you choose to try one anyway, pick named strains and set a clear time limit.

When it might not be IBS

IBS shouldn't be used to explain everything. Go back to your doctor if you notice blood in your stool, weight loss you can't explain, anemia, symptoms that wake you at night, or symptoms that start or change sharply after 50. A family history of colon cancer, celiac disease or inflammatory bowel disease also matters. None of these means something serious is happening, but they change which tests make sense.

If IBS is confirmed, treat it like any long-term condition: one change at a time, tracked for several weeks. If you're adding a soluble fiber, Gentle Fiber is one option, with 6 g of partially hydrolyzed guar gum (PHGG) per stick and no inulin or psyllium.

Sources

1. Mearin F, Lacy BE, Chang L, et al. Bowel disorders. Gastroenterology. 2016;150(6):1393-1407. PMID 27144627
2. Oka P, Parr H, Barberio B, Black CJ, Savarino EV, Ford AC. Global prevalence of irritable bowel syndrome according to Rome III or IV criteria: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2020;5(10):908-917. PMID 32702295
3. Lovell RM, Ford AC. Effect of gender on prevalence of irritable bowel syndrome in the community: systematic review and meta-analysis. Am J Gastroenterol. 2012;107(7):991-1000. PMID 22613905
4. Lacy BE, Pimentel M, Brenner DM, et al. ACG clinical guideline: management of irritable bowel syndrome. Am J Gastroenterol. 2021;116(1):17-44. PMID 33315591
5. Klem F, Wadhwa A, Prokop LJ, et al. Prevalence, risk factors, and outcomes of irritable bowel syndrome after infectious enteritis: a systematic review and meta-analysis. Gastroenterology. 2017;152(5):1042-1054.e1. PMID 28069350

This article is for general information and isn't medical advice. Talk to your healthcare provider before starting a new treatment for IBS, or if your symptoms change.