If you’ve been through a diverticulitis flare (maybe more than once), you know the routine. Severe pain, antibiotics or a hospital stay, a liquid diet, then a slow climb back to normal.
And then it’s supposed to be over.
Except for a lot of people, it isn’t quite over. The dull ache that comes and goes. The bloating that never fully settles. Bowel habits that stay unpredictable long after the flare has technically resolved.
A study published this year in Scientific Reports looked at the gut bacteria of people stuck in exactly that in-between zone — and the results may finally explain why.
Below is a video we made; there is also a written version underneath.
The Condition Most Doctors Never Name
There’s a term for this middle ground that most patients, and plenty of GPs, have never heard: SUDD, or symptomatic uncomplicated diverticular disease.
Diverticular disease actually moves through three distinct states. The first is diverticulosis: you have the small pouches in the colon wall, but no symptoms and no inflammation. Most people with this never even know they have it. The second is diverticulitis itself — active inflammation or infection in one of those pouches, causing fever and severe, localized pain, sometimes requiring hospitalization.
SUDD sits in between. You’ve had flares before, you’re not in one right now, but you’re not fully well either. You’re still experiencing ongoing abdominal pain, bloating, and irregular bowel habits that just linger. This middle state has historically been poorly understood and is often written off as IBS. However, the new research starts to explain what’s actually driving it.
Summary: Diverticular disease has three stages — symptom-free diverticulosis, active diverticulitis flares, and a poorly understood middle zone called SUDD, where lingering symptoms persist without an active flare. SUDD is frequently mislabeled as IBS because doctors haven’t had strong evidence for what causes it — until now.
What the New 2026 Study Actually Found
The research came out of Japan, run across five hospitals, comparing stool samples from three groups: 29 people diagnosed with SUDD, 35 people who had diverticula but no ongoing symptoms, and 68 healthy people with no diverticula at all as controls.
Two findings stood out. First, people with SUDD had noticeably higher levels of a bacterium called Ruminococcus gnavus compared to both other groups (1). This species is associated with inflammation and is known to break down the protective mucus lining of the gut, and it’s also been found at elevated levels in other digestive conditions, including Crohn’s disease and IBS (2).
Second, the SUDD group had significantly lower levels of a bacterial family called Coprococcus. This family plays a key role in fermenting dietary fiber into short-chain fatty acids — compounds that matter far more than most people realize for gut health.
It’s also worth noting the limits here: this was an exploratory, observational study with a relatively small SUDD group (29 people), conducted entirely in a Japanese population, so it can’t establish cause and effect and will need to be replicated in Western populations. Still, it’s a meaningful, peer-reviewed human study, one of the first of its kind to look specifically at this in-between state.
Summary: A 2026 Japanese study compared gut bacteria across three groups and found that people with SUDD had elevated levels of an inflammatory, mucus-degrading bacterium (Ruminococcus gnavus) and depleted levels of a fiber-fermenting bacterial family (Coprococcus). While the study is limited, it’s the clearest human evidence yet that gut bacteria differ in this overlooked middle stage of diverticular disease.
Why Losing Butyrate-Producing Bacteria Matters
The short-chain fatty acids produced by bacteria like Coprococcus, particularly one called Butyrate, are essentially fuel for the cells lining your colon. Butyrate keeps the tight junctions between those cells sealed, maintains the protective mucus layer, and keeps inflammation in check. Think of it as the maintenance crew constantly repainting and patching the inside wall of your gut.
When butyrate-producing bacteria decline, that lining becomes more vulnerable. The gut wall can become more permeable (sometimes called “leaky gut”), allowing substances that should stay contained to cross into the bloodstream.
This doesn’t necessarily cause an acute flare, but it can create the kind of low-grade, chronic irritation that shows up as the persistent pain, bloating, and bowel changes typical of SUDD.
Summary: Butyrate, produced by bacteria like Coprococcus, maintains the gut lining’s integrity and keeps inflammation low. When these bacteria are depleted, the gut wall becomes more permeable, which may explain the chronic, low-level symptoms people experience between flares — even without a full-blown flare occurring.
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What This Means for You Right Now
The practical takeaway centers on feeding the right bacteria. Butyrate is produced when gut bacteria ferment specific fibers, particularly fermentable fiber and resistant starch, found in foods like cooked-and-cooled potatoes, green bananas, oats, and legumes.
But fiber isn’t a one-size-fits-all fix, especially for anyone near a flare or sensitive to FODMAPs. The type, amount, and timing of fiber all matter, and they matter differently for each person. This study reinforces something worth taking seriously: the gut microbiome isn’t a passive bystander in diverticular disease — it may be an active driver of whether someone experiences these in-between symptoms.
The encouraging part is that the microbiome isn’t fixed. It responds to diet, sleep, stress, antibiotic history, and activity levels. But because the specific pattern of bacterial imbalance will differ from person to person, generic advice will always underperform compared to proper testing and a personalized approach.
Summary: Butyrate-boosting foods like resistant starch and fermentable fiber are a practical lever, but fiber tolerance varies widely, especially near a flare. Because gut bacteria patterns differ between individuals, a personalized approach — informed by testing — will outperform generic dietary advice for managing SUDD symptoms.
The IBS Overlap and Why It Matters
One more thread worth pulling: the same bacterium elevated in SUDD in this study, Ruminococcus gnavus, has also been found elevated in other digestive disorders, including IBS with diarrhea. Many people with a diverticular disease diagnosis have also wondered whether they have IBS, and the symptom overlap is real. This study raises the possibility that the two conditions may share a common microbial driver in some people, though the exact mechanism isn’t yet clear.
Summary: The bacterium linked to SUDD symptoms also shows up in IBS, hinting at a possible shared microbial mechanism between the two conditions — though this connection needs further research to confirm.
What Should Your Next Steps Be?
This new research is the clearest human evidence so far that gut bacteria composition looks different in people with lingering diverticular symptoms between flares — lower butyrate producers and higher Ruminococcus gnavus. Whether these bacterial shifts are causing the symptoms or resulting from them isn’t settled yet, but the pattern is real, and it points squarely at the microbiome as something worth investigating rather than ignoring.
If you’re dealing with ongoing symptoms in that in-between zone and want more than generic advice, understanding what’s actually happening in your gut through proper testing is the logical next step toward a personalized plan.
That’s exactly what we built our 4-SURE pathway. It’s a structured process that identifies whether you have the right eating pattern in place, whether the right tests have been done, and what your actual next step is based on your specific situation.
To learn more about our integrated approach, I invite you to apply for a nutrition assessment call with us. We’ll help you make sense of what’s really happening and map out the next steps to get you feeling confident again — not just temporarily avoiding symptoms, but addressing the root cause and fixing your gut issues for good.
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