When Fibromyalgia and IBS Collide: What a New Study Reveals About the Gut–Brain Connection

If you live with fibromyalgia, irritable bowel syndrome (IBS), or both, you’re not imagining it. These two conditions seem to “travel together” a lot.

A 2025 systematic review published in Cureus found that fibromyalgia and irritable bowel syndrome (IBS) frequently co-occur and share overlapping mechanisms involving the immune system, gut microbiome, neurotransmitters, and the gut–brain axis.

Many people with fibro also struggle with bloating, cramping, constipation, diarrhea, or all of the above. Others start with IBS and, over time, develop widespread body pain, fatigue, and brain fog that point toward fibromyalgia. It can feel like your whole system is on overload.

A new systematic review (a high-level study that pulls together many other studies) looked closely at how fibromyalgia and IBS might be connected—and what’s going on in the gut, brain, and immune system when they show up together.

This blog will present the findings in clear, everyday language, and then we’ll discuss what it might mean for you on your healing journey.

Big Picture: Fibro and IBS Are “Cousins,” Not Strangers

Researchers have known for a while that fibromyalgia and IBS often overlap:

• 28–59% of people with fibromyalgia also have IBS

• 32–77% of people with IBS also have fibromyalgia

Both conditions are more common in women and often take years to diagnose. They share many symptoms:

• Pain

• Fatigue

• Poor sleep

• Sensitivity to stress

• Anxiety and depression

Because the symptoms are so similar and both are “diagnoses of exclusion,” people can bounce from specialist to specialist for years before they get answers.

This new review pulled together 10 high-quality studies published between 2015 and 2025 and asked:

What is actually happening in the body when fibro and IBS show up together?

The themes they found are powerful — and hopeful:

1. The immune system is on high alert and somewhat misdirected.

2. The gut microbiome (your inner ecosystem) is out of balance.

3. Neurotransmitters like serotonin, dopamine, glutamate, and GABA are disrupted.

4. The gut–brain axis — the two-way communication between your gut and nervous system — is off-kilter.

Let’s unpack these.

1. The Immune System: When Your Body’s “Alarm System” Gets Stuck On

Think of your immune system as a team of guardians watching for threats. In this review, researchers found that in both fibromyalgia and IBS, the system seems to be:

• Overactivated

• Inflamed

• Not shutting off properly

Some of the key players:

• Mast cells – immune cells that release histamine and other chemicals. When overactivated, they can irritate nerves, increase pain, and stir up gut symptoms.

• Pro-inflammatory cytokines – chemical messengers (like TNF-α and various interleukins) that signal “danger” and drive inflammation.

In IBS, this immune activation can damage the gut lining, making the intestines more sensitive. In fibromyalgia, systemic inflammation contributes to widespread pain and crushing fatigue.

Stress also plays a significant role. The body’s stress system — the HPA axis (hypothalamic–pituitary–adrenal) — pumps out stress hormones like cortisol and CRH (corticotropin-releasing hormone. It’s one of the key hormones involved in activating the body’s stress response through the HPA axis.

Chronic stress:

• Activates mast cells

• Increases inflammatory cytokines

• Worsens both pain and digestive symptoms

This creates a vicious cycle:
Pain and GI distress → stress → more inflammation → more pain and GI distress.

2. Gut Dysbiosis & “Leaky” Barriers: When Your Inner Ecosystem Is Out of Balance

The review also highlighted gut dysbiosis — an imbalance in the trillions of microbes that live in our intestines.

In both IBS and fibromyalgia, researchers have found:

• Reduced beneficial bacteria, including certain Bifidobacteria and other species that:

  • Make short-chain fatty acids (SCFAs) like butyrate

  • Help maintain the gut lining

  • Support a healthy blood–brain barrier

  • Produce calming neurotransmitters like GABA

• Increased populations of other bacteria that may promote:

  • Inflammation

  • Pain sensitivity

  • Changes in gut motility (how quickly food moves through)

When this inner ecosystem is out of balance:

• The gut barrier can become “leaky,” allowing fragments of bacteria and inflammatory molecules to slip through into the bloodstream.

• This can trigger systemic inflammation, affect the nervous system, and contribute to both widespread pain (fibro) and gut pain/sensitivity (IBS).

Some people with fibromyalgia also have small intestinal bacterial overgrowth (SIBO), where bacteria move into parts of the small intestine where they don’t belong. This can cause gas, bloating, and pain — and may feed into the inflammation and sensitization loop.

In simple terms:

When the gut ecosystem is disturbed, the gut wall and even the blood–brain barrier can become more permeable, letting in signals that amplify pain, fatigue, and mood symptoms.

3. Serotonin, Tryptophan & Friends: The Chemistry of Pain and Sensitivity

The review found that neurotransmitters (the chemical messengers that help nerves communicate) are a big part of the story.

A few key ones:

• Serotonin (5-HT) – involved in pain perception, gut motility, mood, and sleep

• Tryptophan (Trp) – an amino acid that is the building block for serotonin

• Glutamate & GABA – glutamate is more “exciting” (can fuel pain and sensitivity), while GABA is calming

• Dopamine – involved in motivation, pleasure, and movement

What the studies suggest:

• In IBS:

  • Serotonin levels in the gut can be elevated, contributing to:

    • Abdominal pain

    • Diarrhea or constipation

    • Hypersensitivity in the intestines

• In fibromyalgia:

  • Serotonin in the central nervous system (brain and spinal cord) seems to be lower.

  • Less serotonin in pain pathways may mean:

    • More pain signals are getting through

    • More sensitivity to touch, pressure, and internal sensations

Tryptophan can be pulled down different metabolic pathways:

• One pathway leads to serotonin (soothing, stabilizing)

• Another leads to kynurenine and eventually quinolinic acid, which can be more neurotoxic and may increase glutamate activity and neuroinflammation.

Under chronic stress and inflammation, the body tends to push more tryptophan down this “stressful” pathway, which means:

• Less tryptophan available for serotonin

• More byproducts that may heighten pain, fatigue, sleep problems, and mood changes

The takeaway:

In people with both fibro and IBS, the combination of gut dysbiosis, immune activation, and altered tryptophan metabolism may skew the whole system toward more pain and less resilience.

4. The Gut–Brain Axis: A Two-Way Highway, Not a One-Way Street

The gut–brain axis is the constant back-and-forth conversation between your intestines and your nervous system. It includes:

• The vagus nerve (a major communication highway)

• The immune system

• Hormones and neurotransmitters

• The microbiome

In healthy conditions, this axis helps regulate digestion, mood, pain, and energy. In IBS and fibromyalgia, this conversation becomes distorted:

• The brain becomes more sensitive to pain signals (central sensitization).

• The gut becomes more reactive, with altered motility and heightened sensitivity to normal sensations, like gas and stretching.

• Immune signals and microbial by-products further amplify the noise in the system.

The review suggests that fibromyalgia + IBS together may reflect a deeper level of gut–brain axis disruption than either condition alone.

5. Probiotics & Fecal Microbiota Transplant (FMT): Hopeful… but Not Ready for Prime Time

Because the gut microbiome appears to be so central, researchers are very interested in therapies that restore a healthier inner ecosystem, including:

• Probiotics – beneficial bacteria taken as supplements or from foods

• Prebiotics – fibers that feed good bacteria

• Fecal microbiota transplant (FMT) – transplanting stool from a healthy donor to someone with dysbiosis (already a standard treatment for recurrent C. difficile infection)

Here’s what this review found:

• Some probiotics (including different Lactobacillus and Bifidobacterium strains) appear to:

  • Reduce some IBS symptoms

  • Support gut barrier function

  • Increase helpful SCFA production

  • Influence the nervous system pathways linked to pain and stress

• In fibromyalgia, a few small studies suggest probiotics may help cognitive and emotional symptoms, but pain relief is inconsistent so far.

• FMT has shown dramatic improvement in at least one case report involving a person with fibromyalgia, IBS, and chronic fatigue — but that’s one person, not a large trial.

The bottom line from the researchers:

• Probiotics and FMT are promising but not yet proven standard treatments for fibromyalgia or IBS.

• We need more high-quality, long-term studies to know:

  • Which strains help which patients

  • What doses work

  • How safe and effective is FMT really for these conditions

So… What Does This Mean for You Right Now?

Here are some gentle, grounded takeaways from this research:

1. You are not “crazy” or “making it up.”
   Fibro + IBS is a real and increasingly understood pattern. Your pain, fatigue, and gut symptoms are rooted in very real shifts in immunity, microbiome balance, and brain–gut communication.

2. Your gut and your nervous system are deeply connected.
   Supporting your gut health isn’t just about digestion; it may also influence pain, mood, sleep, and energy.

3. Stress management isn’t optional “self-care fluff” — it’s biology.
   Because the stress system (HPA axis) influences inflammation, gut permeability, and pain, anything that gently helps you downshift — such as breathing, mindfulness, pacing, time in nature, or restorative movement — is part of your healing toolkit.

4. Food and microbiome support matter.
   While this review focused on mechanisms rather than specific diets, it reinforces the idea that:

   • Reducing gut irritation and inflammation

   • Supporting beneficial bacteria (through fiber-rich foods, possibly probiotics, and individualized nutrition)
     may be meaningful pieces of the fibromyalgia-IBS puzzle.

5. We’re at the beginning of a more hopeful chapter.
   The review calls for:

   • Better research on gender differences (since women are more affected)

   • Studies that specifically include people who have both FM and IBS

   • Trials of microbiome-targeted therapies and serotonin-related medications tailored to this overlap

This is not about “fixing everything overnight.” It is about understanding your body more deeply, so you can make aligned choices and advocate for yourself in the medical system.

A FibroSoul Perspective: Tending the Inner Ecosystem

At FibroSoul, we look at fibromyalgia not just as a list of symptoms, but as a whole-system story:

• Your nervous system

• Your immune system

• Your gut

• Your hormones

• Your emotions

• Your spirit

All of these are in conversation, all the time.

This research on fibromyalgia and IBS reminds us that healing is not just about chasing pain — it’s about tending the inner ecosystem of your body with as much compassion and curiosity as possible.

In the coming FibroSoul resources, we’ll keep exploring:

• How nutrition and the microbiome may shift pain and energy

• Gentle ways to support the gut–brain axis

• Tools for nervous system regulation, pacing, and rest

• Ways to work with your care team to explore options like probiotics, SIBO testing, and more — always safely and individually

For now, you might pause, place a hand over your belly or your heart, and simply acknowledge:

My body is complex, but it is not broken. There are reasons for how I feel — and slowly, science is catching up to what I’ve known in my bones: everything is connected.

You deserve care that sees the whole of you — body, mind, and soul.