Fatty liver disease is linked to a higher rate of chronic diarrhea than you’d expect from chance alone, and there are several plausible biological reasons why. A large U.S. population study found that people with presumed fatty liver disease had roughly a third higher odds of chronic diarrhea compared to those with normal bowel habits, even after accounting for body weight and other metabolic conditions. The connection is not as straightforward as, say, food poisoning causing stomach trouble. Instead, multiple overlapping pathways tie the liver’s fat accumulation to disrupted digestion, and some of the medications used to treat the disease can make things worse.
What the Population Data Actually Show
The clearest large-scale evidence comes from an analysis of U.S. national health survey data, which found that the prevalence of presumed fatty liver disease was about 13% among people reporting chronic diarrhea, compared to roughly 9.5% among people with normal bowel patterns. After adjusting for demographics, smoking, alcohol, body mass index, and other metabolic conditions, fatty liver disease was independently associated with diarrhea, with about 34% higher odds compared to normal bowel habits.1BMJ Open Gastroenterology. Associations of chronic diarrhoea with non-alcoholic fatty liver disease and obesity-related disorders among US adults That’s a modest but statistically meaningful increase, and it held up even when the researchers controlled for obesity on its own, meaning the fatty liver itself seems to contribute something beyond just being overweight.
A separate prospective study of 127 patients with confirmed fatty liver disease found a strikingly high rate of chronic diarrhea: one in four patients reported it. About half of those diarrhea cases showed features of bile acid diarrhea specifically, and having diarrhea was associated with a higher liver fibrosis score, suggesting the bowel problems tracked with disease severity.2PLOS ONE. Non-alcoholic fatty liver disease is associated with dysregulated bile acid synthesis and diarrhea: A prospective observational study So this is not just a quirk of survey data. Something about fatty liver disease appears to genuinely push the gut toward looser, more frequent stools.
Bile Acids Gone Wrong
The most well-studied mechanism connecting fatty liver to diarrhea involves bile acids, the compounds your liver makes from cholesterol to help digest fats. In a healthy system, the liver produces bile acids, the small intestine uses them to absorb fats, and then the end of the small intestine reabsorbs most of them and sends them back to the liver for recycling. This loop is tightly regulated by a signaling molecule called FGF19, which tells the liver how much bile acid is enough.
In fatty liver disease, this feedback loop goes haywire. The liver tends to overproduce bile acids, and the signaling that should put the brakes on that production weakens. The prospective study mentioned above found that patients with fatty liver disease and diarrhea had lower levels of FGF19 and higher levels of C4, a marker of increased bile acid production.2PLOS ONE. Non-alcoholic fatty liver disease is associated with dysregulated bile acid synthesis and diarrhea: A prospective observational study When excess bile acids spill into the colon, they pull water into the intestine and speed up motility. The result is watery, urgent stools, sometimes several times a day.
A retrospective cohort study using a specialized test for bile acid absorption (the SeHCAT scan) confirmed this overlap from the other direction. Among patients being evaluated for bile acid diarrhea, those with poor bile acid absorption were roughly three times more likely to also have fatty liver on imaging combined with elevated liver enzymes.3BMJ Open Gastroenterology. Novel associations of bile acid diarrhoea with fatty liver disease and gallstones: a cohort retrospective analysis In other words, bile acid diarrhea and fatty liver cluster together, likely because they share disrupted bile acid signaling as a root cause.4PubMed Central. Bile Acid Diarrhea and NAFLD: Shared Pathways for Distinct Phenotypes
A Leaky Gut and Bacterial Overgrowth
Bile acid disruption isn’t the only pathway. Fatty liver disease is also associated with increased intestinal permeability, sometimes called “leaky gut,” where the lining of the intestine becomes less effective at keeping its contents where they belong. Bacterial fragments, particularly lipopolysaccharides (LPS), can leak through the weakened barrier and travel to the liver, fueling inflammation there.5PubMed Central. The Role of Gut-Derived Lipopolysaccharides and the Intestinal Barrier in Fatty Liver Diseases But the traffic runs both ways: liver inflammation and fat accumulation appear to worsen gut barrier function, creating a self-reinforcing cycle.6Frontiers in Endocrinology. Endotoxins and Non-Alcoholic Fatty Liver Disease
Alongside this barrier problem, people with fatty liver disease are considerably more likely to have small intestinal bacterial overgrowth, or SIBO, where bacteria that should be concentrated in the colon colonize the small intestine instead. A meta-analysis pooling ten studies with over 1,000 participants found that fatty liver disease was associated with nearly four times the odds of SIBO.7European Journal of Gastroenterology & Hepatology. Small intestinal bacterial overgrowth and nonalcoholic fatty liver disease: a systematic review and meta-analysis SIBO can cause diarrhea through several channels: the misplaced bacteria interfere with fat absorption, deconjugate bile salts (making them less effective and more irritating to the colon), and ferment carbohydrates in places where that fermentation produces gas and draws water into the intestine.8PubMed Central. Small Intestinal Bacterial Overgrowth and Non-Alcoholic Fatty Liver Disease: What Do We Know in 2023?
So if you have fatty liver disease and persistent loose stools, it might not be the liver directly causing trouble. It could be that bacterial overgrowth in your small intestine, fed by the same metabolic conditions that caused the fatty liver, is the more immediate culprit.
When the Medications Are Making It Worse
Here’s where things get frustrating for patients: some of the most promising treatments for fatty liver disease list diarrhea as a common side effect. If you’ve started a new medication and your bowel habits changed around the same time, the drug itself may be the reason.
Resmetirom, the first drug specifically approved for fatty liver disease with fibrosis, causes diarrhea at notably higher rates than placebo. In the pivotal phase 3 trial, between roughly 24% and 31% of patients on resmetirom experienced diarrhea, compared to about 14% on placebo. The episodes were mostly mild to moderate and tended to cluster in the first 12 weeks of treatment, tapering off after that, with a median duration of about two to three weeks.9Nature Medicine. Resmetirom for nonalcoholic fatty liver disease: a randomized, double-blind, placebo-controlled phase 3 trial Meta-analyses of resmetirom trials confirmed that the drug roughly doubles the likelihood of diarrhea compared to placebo.10PubMed Central. Efficacy and safety of resmetirom among patients with non-alcoholic steatohepatitis: a systematic review and meta-analysis
GLP-1 receptor agonists, increasingly used for fatty liver disease because of their effects on weight and liver fat, bring their own gastrointestinal burden. A systematic review found that about 20% of patients using these drugs for fatty liver disease experienced diarrhea, and roughly 59% experienced some form of gastrointestinal side effect overall.11Frontiers in Medicine. Gastrointestinal adverse events associated with GLP-1 receptor agonists in metabolic dysfunction-associated steatotic liver disease (MASLD): a systematic review and meta-analysis Metformin, commonly prescribed for the diabetes that often accompanies fatty liver disease, is another well-known offender. The prospective bile acid study found that metformin use was significantly associated with diarrhea and altered bile acid signaling, compounding the problem in patients who already have disrupted bile acid metabolism.2PLOS ONE. Non-alcoholic fatty liver disease is associated with dysregulated bile acid synthesis and diarrhea: A prospective observational study
The practical upshot: if you have fatty liver disease and develop new or worsening diarrhea after starting a medication, it’s worth talking to your doctor about timing and dosage before assuming the liver disease itself is to blame.
The Pancreas Connection
Your pancreas secretes digestive enzymes that break down fats, proteins, and carbohydrates. When the pancreas underperforms, a condition called pancreatic exocrine insufficiency, undigested food (especially fat) passes through to the colon and causes greasy, foul-smelling diarrhea. This is a different kind of diarrhea from the watery, urgent type caused by bile acids, and it comes with its own clues: oily stools, bloating, and sometimes unintentional weight loss.
An emerging area of research suggests that fatty liver disease may be associated with reduced pancreatic enzyme output. One study found that patients with fatty liver disease had significantly lower fecal elastase levels (a marker of pancreatic function) compared to healthy controls, and that over 84% of fatty liver patients met laboratory criteria for pancreatic exocrine insufficiency.12Egyptian Liver Journal. Evidence of Pancreatic Exocrine Insufficiency in patients with Metabolic Associated Fatty Liver Disease patients That’s a surprisingly high number, and the researchers identified fatty liver disease as an independent predictor of pancreatic insufficiency.
That said, the evidence here is still early. A pilot study that went a step further, measuring actual fat digestion capacity in patients with low elastase, found that none of those patients had clinically meaningful fat malabsorption when tested with a more direct method.13PubMed. Non-alcoholic fatty pancreas disease and pancreatic exocrine insufficiency: pilot study and systematic review In other words, the lab test might flag reduced enzyme levels that haven’t yet translated into real digestive problems. This is an area where jumping to pancreatic enzyme supplements based on one blood test could lead to unnecessary treatment, so a careful workup matters.
How Advanced Liver Disease Changes the Picture
Everything discussed so far applies to fatty liver disease across its spectrum, from simple fat accumulation through inflammation and early scarring. But when fatty liver progresses to cirrhosis, the digestive problems often escalate. Cirrhosis brings its own layer of gut dysfunction: delayed stomach emptying, slowed transit through the small intestine, and worsened bacterial overgrowth.14PubMed Central. Gastrointestinal dysfunction in liver cirrhosis The portal hypertension that develops in advanced cirrhosis can cause fluid to weep into the intestinal wall, further disrupting absorption. Some patients develop a condition where the colon becomes engorged with dilated blood vessels, which can cause chronic watery diarrhea on its own.
People with cirrhosis from any cause, including fatty liver, also tend to have more pronounced gut barrier breakdown and bacterial translocation, which feeds back into worsening liver inflammation and the systemic inflammatory state that characterizes decompensated liver disease. If someone with known fatty liver suddenly develops persistent diarrhea along with other red flags like abdominal swelling, easy bruising, or confusion, the priority should be evaluating for cirrhosis progression rather than attributing the diarrhea to any of the milder mechanisms above.
Irritable Bowel Syndrome and the Overlap Problem
One complication in untangling this picture is that fatty liver disease frequently coexists with irritable bowel syndrome, particularly the diarrhea-predominant type. Population data show that the prevalence of fatty liver is higher in people with diarrhea-predominant IBS (about 13%) than in those with constipation-predominant IBS (about 9%).15PubMed Central. Non-alcoholic fatty liver disease in irritable bowel syndrome: More than a coincidence? A systematic review of the overlap between these two conditions concluded that their association is likely mediated through shared pathways, particularly altered bile acid metabolism, gut microbiome changes, and low-grade inflammation.16PubMed Central. Associations between irritable bowel syndrome and non-alcoholic fatty liver disease: A systematic review
This overlap matters practically because the diarrhea a fatty liver patient experiences might already be categorized as IBS, which is typically treated as a functional disorder with dietary modification and symptom management. If the underlying bile acid overproduction or bacterial overgrowth isn’t identified, those standard IBS treatments may not work well. Bile acid sequestrants, for instance, can be effective when bile acid diarrhea is the real driver, but they’re rarely the first thing a clinician reaches for when the diagnosis on the chart says IBS.
Inflammatory bowel disease is a separate issue worth mentioning. A nationwide population-based study found a statistically significant increase in fatty liver disease risk among patients with IBD.17Intestinal Research. Association between nonalcoholic fatty liver disease and incidence of inflammatory bowel disease: a nationwide population‑based cohort study The relationship between IBD and fatty liver probably runs through chronic inflammation, medication effects, and metabolic changes rather than through the bile acid pathways discussed earlier. If your diarrhea is bloody, accompanied by significant weight loss, or came on suddenly, IBD should be on the differential regardless of whether you also have fatty liver.
Children Are Not Immune
Fatty liver disease is no longer an adult problem. As childhood obesity rates have climbed, so has pediatric fatty liver disease, and the digestive symptoms appear to follow. A cross-sectional study comparing children with fatty liver to healthy controls found that diarrhea, along with reflux, abdominal pain, and indigestion, was significantly more common in the fatty liver group.18PubMed Central. Association Between Gastrointestinal Symptoms and Sleep Habits in Children with Metabolic Dysfunction-Associated Steatotic Liver Disease: A Cross-Sectional Study A separate study of children with fatty liver disease found that those with the condition had diarrhea more frequently than children with obesity alone or healthy-weight controls, and the diarrhea was linked to a higher rate of small intestinal bacterial overgrowth.19Gastroenterologia. Association of small intestinal bacterial overgrowth and non-alcoholic fatty liver disease in children
Pediatric cases deserve special attention because chronic diarrhea in children can quickly lead to nutritional deficiencies and growth concerns. Parents who know their child has fatty liver disease should flag persistent bowel changes to their pediatrician rather than assuming it’s just a sensitive stomach. SIBO in children is treatable with targeted antibiotics, and addressing it may improve both the gut symptoms and the liver disease trajectory.
Dietary Fructose and the Gut-Liver Loop
Diet is where many patients have the most control, and it’s also where the gut and liver are most directly connected. High fructose intake is a recognized driver of fatty liver disease, and the damage starts in the intestine itself. Fructose metabolism in the small intestine can impair the gut barrier and shift the microbial community, allowing more lipid-building substrates and bacterial products to reach the liver.20PubMed Central. The Contribution of Dietary Fructose to Non-alcoholic Fatty Liver Disease High-fructose foods, particularly sweetened beverages and processed snacks, can also cause osmotic diarrhea directly when consumed in amounts that overwhelm the small intestine’s absorption capacity. Many adults have limited fructose absorption ability and don’t realize it.
This means that the dietary pattern contributing to your fatty liver may simultaneously be causing your diarrhea through a completely independent mechanism. Reducing fructose intake can potentially improve both the liver condition and the bowel symptoms, making it one of the more straightforward interventions available. It won’t fix bile acid overproduction or bacterial overgrowth on its own, but it removes one contributing factor from a system that already has too many things going wrong at once.
What to Tell Your Doctor
If you have fatty liver disease and chronic diarrhea, the worst thing you can do is assume they’re unrelated or that the diarrhea is just something you have to live with. Several of the mechanisms behind the connection are treatable, but they require different approaches. Bile acid diarrhea responds to bile acid sequestrants. SIBO can be addressed with specific antibiotics. Medication-induced diarrhea often improves with dose adjustments or switching agents. Pancreatic insufficiency, if confirmed with proper testing, can be managed with enzyme supplements.
The challenge is that diagnosing the right mechanism takes some work. Stool tests, breath tests for SIBO, blood markers for bile acid overproduction, and sometimes imaging are needed to sort through the possibilities. A gastroenterologist who is aware of the gut-liver connections outlined here is better positioned to order the right workup than a general practitioner who may default to an IBS diagnosis. Keep a simple log of your bowel habits, noting stool consistency, frequency, urgency, and any relationship to meals or medications. That kind of specific information helps narrow the field faster than vague reports of “stomach trouble.”