Persistently loose stools usually point to one of a handful of causes: your diet, a medication you’re taking, or an underlying digestive condition that speeds up your bowel or prevents it from absorbing water and nutrients properly. If your stools have been soft, mushy, or watery for weeks rather than days, something is consistently disrupting the way your colon processes waste. The good news is that most causes are identifiable and treatable once you know where to look.
What “Loose” Actually Means
The Bristol Stool Chart, a visual scale used by gastroenterologists, classifies stool into seven types. Types 5 through 7 all fall into the loose category. Type 5 is soft blobs with clear-cut edges. Type 6 is fluffy, mushy pieces with ragged edges. Type 7 is entirely liquid with no solid pieces at all. All three suggest your bowels are moving too fast, pushing contents through before enough water gets absorbed.
Having a Type 5 stool once in a while is normal. The concern starts when you rarely or never produce a formed stool, particularly Types 6 and 7 on a regular basis. Chronic loose stools, generally defined as lasting four weeks or more, deserve investigation beyond just “something I ate.”
Dietary Causes That Keep Stools Soft
Certain carbohydrates are poorly absorbed by the small intestine. When they reach the colon intact, bacteria ferment them and produce gas. At the same time, these unabsorbed sugars pull water into the bowel through osmosis, making stool looser and more urgent. This group of carbohydrates, collectively called FODMAPs, includes fructose (in fruit, honey, and high-fructose corn syrup), lactose (in dairy), sorbitol and mannitol (in sugar-free gum and some stone fruits), and certain fibers found in wheat, onions, and garlic.
The effect is dose-dependent. A small amount of fructose might not bother you, but a smoothie with mango, honey, and apple juice could tip you over the threshold. Many people with chronically loose stools discover that their gut handles each of these sugars differently, tolerating some but not others. A structured elimination diet, where you remove all high-FODMAP foods for two to six weeks and then reintroduce them one category at a time, is the standard way to identify your personal triggers.
Caffeine and alcohol also speed up bowel motility directly. If you drink several cups of coffee a day or have regular alcohol intake, that alone can keep your stools perpetually soft.
Medications That Cause Chronic Loose Stools
If your loose stools started around the time you began a new medication, that’s worth flagging. Metformin, one of the most widely prescribed drugs for type 2 diabetes, is a well-known offender. It appears to increase intestinal motility and reduce bile salt absorption in the small intestine. Those unabsorbed bile salts then reach the colon and trigger a secretory effect that pulls water into the bowel. For some people, metformin-related diarrhea shows up early. For others, it can develop years into treatment.
Antibiotics disrupt gut bacteria and can cause loose stools that persist for weeks after the course ends. Magnesium supplements, antacids containing magnesium, certain blood pressure medications, and SSRIs (a common class of antidepressants) can all soften stool as well. If you suspect a medication, don’t stop it on your own, but do bring it up with your prescriber, because alternatives or dose adjustments often exist.
Bile Acid Malabsorption
This is one of the most underdiagnosed causes of chronic loose stools. Your liver produces bile acids to help digest fat. Normally, the end of your small intestine reabsorbs about 95% of them. When that recycling system fails, excess bile acids flood the colon and cause watery diarrhea, often urgently and sometimes multiple times a day.
Studies estimate that 25% to 30% of people investigated for chronic unexplained diarrhea turn out to have bile acid malabsorption. One study of patients who met the diagnostic criteria for diarrhea-predominant irritable bowel syndrome found that 24% actually had bile acid malabsorption when formally tested. That means a significant number of people walking around with an “IBS” label may have a different, specifically treatable condition. A bile acid binder medication often resolves symptoms within days when this is the cause.
IBS With Diarrhea
Irritable bowel syndrome with diarrhea (IBS-D) is diagnosed when you have recurrent abdominal pain linked to bowel movements, along with a change in stool frequency or form, for at least six months. There’s no single test that confirms it. Instead, it’s diagnosed after other conditions have been ruled out.
IBS-D tends to involve cramping that eases after a bowel movement, urgency, and loose stools that cluster in the morning or after meals. Stress and anxiety frequently make it worse, because the gut and brain share nerve pathways that influence motility. Unlike inflammatory bowel disease, IBS doesn’t cause visible damage to the intestinal lining. A stool test measuring a protein called calprotectin can help distinguish between the two: levels below 50 micrograms per gram strongly suggest IBS rather than inflammatory disease, with a higher cutoff of 100 pushing the negative predictive value to 97%.
Microscopic Colitis
If you’re a woman over 50 with persistent watery diarrhea that doesn’t respond to dietary changes, microscopic colitis is worth considering. This condition causes inflammation in the colon lining that looks completely normal during a standard colonoscopy. It’s only visible under a microscope, which is why biopsies are essential for diagnosis.
There are two subtypes, collagenous colitis and lymphocytic colitis, but both present the same way: chronic watery diarrhea, sometimes with mild cramping. Certain medications, including proton pump inhibitors and NSAIDs like ibuprofen, have been linked to triggering it. Treatment typically brings significant relief.
Signs Your Stools May Be Fatty
Not all loose stools are the same. If yours are pale or clay-colored, greasy, unusually bulky, foul-smelling, foamy, or hard to flush, you may be passing undigested fat. This is called steatorrhea, and it points to a different set of problems than watery diarrhea. It can mean your pancreas isn’t producing enough digestive enzymes, your body isn’t absorbing fat properly due to celiac disease or another small intestine condition, or bile flow from your liver is blocked.
Fatty stools often float and may leave an oily film in the toilet. If this description matches what you’re seeing, it’s a meaningful clue that narrows the diagnostic search considerably.
How Doctors Investigate Chronic Loose Stools
The workup typically starts with blood tests looking for signs of inflammation, celiac disease antibodies, thyroid function (an overactive thyroid speeds up the gut), and markers of nutritional deficiency that would suggest malabsorption. A stool sample can check for infections, calprotectin levels to screen for inflammatory bowel disease, and fecal fat content if steatorrhea is suspected.
If initial tests are inconclusive, a colonoscopy with biopsies may follow, particularly to rule out microscopic colitis or inflammatory bowel disease. Testing for bile acid malabsorption is less standardized, especially in the United States, but some doctors will try a therapeutic trial of a bile acid binder to see if symptoms resolve, which serves as both a diagnostic and treatment step.
Patterns Worth Paying Attention To
Before your appointment, tracking a few details can speed up diagnosis significantly. Note whether loose stools happen after meals, in the morning, or unpredictably throughout the day. Pay attention to whether certain foods reliably trigger them. Record whether you also have bloating, gas, cramping, urgency, or any sense of incomplete evacuation.
Certain features raise the level of concern. Unintentional weight loss, blood in the stool, diarrhea that wakes you from sleep, or signs of anemia like unusual fatigue or pallor suggest something beyond a functional disorder and warrant prompt evaluation. But even without those red flags, chronically loose stools that interfere with your daily life or have persisted for more than a month are worth investigating. Dehydration and nutritional deficiencies can develop gradually when your bowel isn’t absorbing properly, even if you otherwise feel fine.