This Gut Hormone Could Explain 40% of IBS-D Cases—and Lead to a Cure

Hey there, friend. If you've been struggling with IBS-Dirritable bowel syndrome with diarrheayou know the drill: endless bathroom trips, stomach cramps, and that awful feeling of being completely out of control. It's exhausting, frustrating, and honestly? Sometimes it feels like no one really understands what you're going through.

But what if I told you that there might be a real biological reason behind your symptoms? Something deeper than just stress or that sandwich you had for lunch?

Meet INSL5a little-known gut hormone that researchers at the University of Cambridge believe may be behind nearly 40% of IBS-D cases, especially those linked to bile acid malabsorption. And yes, this discovery might lead to a simple blood test and even an actual, real treatment path for chronic diarrhea. No more guesswork.

What Makes IBS-D Different?

Let's start from the beginning. IBS-D isn't just regular IBS with extra bathroom breaks. The "D" stands for diarrhea-predominant, and it means your gut is moving things along a little too quickly. This fast transit leads to loose stools, urgency, and sometimes painful cramps that feel like your body's in overdrive.

One of the key players behind this chaos is bile acid malabsorption (BAM). Picture bile acids as helpful little ferryboats that carry fats through your digestive system. Normally, they get reabsorbed in the last part of your small intestine and recycled. But in some people, they escape into the colonwhere they act like a laxative, triggering explosive diarrhea.

And here's where things get interesting

The Hormone Behind the Chaos

When bile acids reach the colon uninvited, something unexpected happens: the body releases a hormone called INSL5. Think of INSL5 as the gut's emergency alarm systemit kicks into high gear when bile acids show up where they shouldn't, sending signals to your intestines that trigger water secretion and muscle contractions.

That's rightthe very hormone meant to keep your gut balanced might actually be the cause of your constant trips to the bathroom. According to a 2025 study from Cambridge, elevated levels of INSL5 were found in a significant number of people with IBS-D who also showed signs of undiagnosed bile acid malabsorption [study].

So how does that compare to other gut hormones like CCK or GLP-1? Well, while these hormones influence digestion and blood sugar regulation, INSL5 has a much more dramatic effect when it comes to stimulating bowel movements. In a way, it's like the gut's version of pressing the gas pedal when you're already going 90 mph.

Hormone	Role in Gut Function	Linked to Diarrhea/Irritation?
INSL5	Responds to bile acids	Strongly linked to IBS-D
CCK	Slows gut motility	Not directly related
GLP-1	Glucose control	Can slow motility
Motilin	Controls migrating motor complexes	Indirectly linked

Can You Actually Be Tested For This?

You're probably thinking, "Okay, so my symptoms match all of this... but how would I actually know for sure?" Fair questionand this is where testing comes in. While there isn't yet a definitive INSL5 blood test widely available (though one is currently in the works), there are ways to check whether bile acid malabsorption might be behind your troubles.

The most reliable option right now is the 7-day stool bile acid test, which involves collecting your poop samples over several days to measure bile acid levels. Though it might sound less than glamorous, it's incredibly effective at identifying BAM. Another option is the SeHCAT scan, a nuclear imaging procedure that tracks bile acid absorptionbut it's not available everywhere, and costs can be high.

A Glimpse Into Future Diagnostics

Imagine taking a quick blood draw and knowing within minutes whether your diarrhea is caused by a specific hormonal imbalance. Sounds like something out of a sci-fi movie, right? Not anymore. Early clinical trials have started working on an INSL5-specific antibody test that could change the game. If successful, it would allow doctors to pinpoint exactly what's happening inside your gutand choose the right treatment without months of trial and error.

Test	Cost	Accuracy	Availability
SeHCAT Scan	$$$	High	Limited
7-day stool bile acid test	$$	Moderate-High	National Labs
New INSL5 blood test	?	Research phase	Coming soon

How Do These Hormone Treatments Work?

Now for the exciting part: treatment. Because once we understand the cause, we can target it directly. Researchers have been exploring ways to block INSL5 from activating the intestines, and early studies suggest that a drug already used for other conditionscalled naltrexonecould have a big impact. This opioid antagonist works by preventing INSL5 from binding to its receptor, essentially turning off the switch that causes diarrhea.

Of course, we still have to ask the important question: what kind of risks are involved with this approach? Any treatment that disrupts hormones isn't something to jump into lightly. The gut is a finely tuned system, and hitting one lever could affect others. That's why experts stress the importance of confirming the presence of BAM or elevated INSL5 before going down this path.

Treatment Type	Mode of Action	Risks	Best For
Hormone Treatments (e.g. INSL5 blockers)	Addresses root trigger	Emerging	Confirmed INSL5/BAM cases
Eluxadoline	Mu-opioid agonist, reduces motility	Constipation risk	Loose stool IBS-D
Rifaximin	Antibiotic, reduces bacterial overgrowth	Temporary relief	SIBO-linked IBS-D
Dietary (Low FODMAP)	Removes fermentable carbs	Nutrient deficiencies if overused	Broad IBS use

The Hidden Influence of Sex Hormones

And here's something else that might surprise you: hormones like estrogen and progesterone can also play a role in IBS-D. Women tend to report higher rates of the condition, and symptoms often worsen around that time of the month. Why? Because estrogen and progesterone don't just affect your mood or cyclethey also influence gut motility and how sensitive you are to abdominal discomfort.

Take the premenstrual phase, for instance. Your estrogen and progesterone levels drop, and chances are, so does your tolerance for anything off-kilter in your digestive tract. Suddenly, that cup of coffee hits different, and a stress-free day turns into a 24-hour rush to the toilet.

Menstrual Phase	Hormone Levels	GI Impact
Late luteal (premenstrual)	Estrogen & Progesterone	Worsened diarrhea, bloating
Ovulation	Estrogen	Variable motility
Menses	Lowest estrogen levels	Rectal sensitivity
Postmenopause	Estrogen	May decrease symptoms or cause constipation

Is This the Real Deal or Just Hype?

Let's address the elephant in the room. It's natural to wonder: Is this really going to change my life, or is it just more medical optimism that fades into thin air?

Well, based on what scientists have discovered about INSL5 and bile acids, there's solid evidence pointing to a breakthrough. Clinical trials are currently underway to test hormone-blocking agents, and early phase results have shown promising signs of reducing chronic diarrhea episodes in patients. Experts expect testing and potentially accessible treatments to become available by 20262027.

Still, there's a critical caveat here: not every case of IBS-D will respond to this treatment. Some people benefit more from diet changes, others from antibiotics like rifaximin, and many from managing their stress and lifestyle habits. What matters most is not rushing to a single solution, but rather walking into your doctor's office with informationand confidence about which tests might give answers.

Steps You Can Take Right Now

So where do you begin?

1. Talk to your doctor about getting tested for bile acid malabsorptionespecially if you've ruled out common triggers like lactose intolerance or gluten issues.
2. Track your symptoms. Are they worse during certain times of the month? After meals? At night? This helps create a clearer picture for your healthcare provider.
3. Stay updated on clinical trials that might include new hormone treatments. Patient registries or online forums can be helpful for staying in the loop.
4. Keep advocating for yourself. If you don't feel heard, get a second opinion. You deserve to understand what's going on in your gut.

Wrapping Up

If you've been waiting for something realsomething backed by science instead of guessworkthis could be it. We're on the edge of a major breakthrough that has the potential to solve one of gastroenterology's biggest mysteries, offering targeted relief for millions of people living with chronic diarrhea.

That's not just excitingit's empowering. Because when you finally have a name for what's causing your symptoms, and a treatment plan built on understanding rather than trial and error, it changes everything. From anxiety to confidence. From frustration to hope. From fumbling in the dark to finally turning on a light.

So go ahead, reach out to your doctor. Ask for a bile acid test. Start tracking your patterns and talking about your concerns. This might just be the start of something betternot only for your gut, but for your entire quality of life.

Wishing you every bit of peace, healing, and joy along the way

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.