Most people with gastroparesis do not have normal bowel habits. While the condition is defined by delayed stomach emptying, its effects rarely stop there. Research shows that roughly a third of gastroparesis patients have delayed colonic transit, and constipation severe enough to affect daily life is common. Some patients swing the other direction and develop chronic diarrhea instead, often driven by secondary problems like bacterial overgrowth or bile acid imbalances. The short version is that gastroparesis tends to disrupt the entire gut, not just the stomach.
Constipation Is the Most Common Bowel Problem
When researchers specifically studied bowel habits in gastroparesis patients, the results were striking. In a large analysis that measured both symptoms and actual transit times, about 34% of patients rated their constipation as severe or very severe, another 24% called it moderate, and only 42% reported none, very mild, or mild constipation. So more than half of gastroparesis patients deal with meaningful constipation. The study also found that delayed colonic transit was present in roughly 32% of the group, confirming that the sluggish motility extends well beyond the stomach for many people.1PubMed Central. Constipation in Patients with Symptoms of Gastroparesis: Analysis of Symptoms and Gastrointestinal Transit
A separate study comparing gastroparesis patients to people with normal gastric emptying found an even higher rate of slow-transit constipation: about 65% of those with confirmed gastroparesis had it, versus 28% of people whose stomachs emptied normally. The same study found that structural pelvic-floor problems like rectocele and intussusception were also significantly more common in the gastroparesis group.2Journal of Neurogastroenterology and Motility. High Prevalence of Slow Transit Constipation in Patients With Gastroparesis
An interesting wrinkle is that the severity of constipation does not appear to track with how delayed your stomach emptying is. In the first study, constipation severity showed no correlation with gastric retention measured on emptying tests. Instead, it correlated with small bowel, colonic, and whole gut transit times. This matters because it suggests constipation in gastroparesis is not simply a downstream effect of food sitting in the stomach too long. The problem runs deeper, involving motility issues throughout the digestive tract.1PubMed Central. Constipation in Patients with Symptoms of Gastroparesis: Analysis of Symptoms and Gastrointestinal Transit
When Gastroparesis Causes Diarrhea Instead
It sounds contradictory: a condition defined by things moving too slowly through the stomach can also cause loose, frequent stools. But diarrhea is a recognized problem in gastroparesis, and it has its own set of mechanisms. In a propensity-matched study comparing gastroparesis patients to those with functional dyspepsia, functional diarrhea was about 68% more common in the gastroparesis group.3PubMed Central. Exploring Clinical Similarities and Distinctions Between Gastroparesis and Functional Dyspepsia: A Propensity‐Matched Cohort Study
Researchers have proposed several pathways for how this happens. When the stomach empties poorly, it can lead to excess acid production. That extra acid floods the small intestine, where it can damage the lining and interfere with fat absorption. The acid also inactivates digestive enzymes and causes bile salts to precipitate, which leads to fatty, greasy stools. On top of that, when only small amounts of food dribble into the duodenum at a time, the body still releases a full dose of bile in response. The result is a lopsided ratio of bile to food, and the excess bile acids can overwhelm the intestine’s ability to reabsorb them. Free bile acids irritate the colon directly, triggering water secretion and faster movement, producing diarrhea in a process similar to bile acid malabsorption syndrome.4PubMed Central. Gastric peroral endoscopic myotomy improves chronic diarrhea in patients with refractory gastroparesis
For some patients, this means alternating between constipation and diarrhea, sometimes in the same week. It is one of the more frustrating aspects of gastroparesis, because the bowel pattern feels unpredictable and can make dietary planning even harder than it already is.
Small Intestinal Bacterial Overgrowth and Its Role
One of the most significant secondary problems in gastroparesis is small intestinal bacterial overgrowth, commonly called SIBO. When the stomach and small intestine move slowly, the normal housekeeping contractions that sweep bacteria downstream between meals become weak or infrequent. Bacteria that should be confined to the colon proliferate in the small intestine instead, where they ferment food and produce gas, bloating, and either diarrhea or constipation depending on the type of overgrowth.
A systematic review pooling data from multiple studies estimated that about 41% of gastroparesis patients have SIBO.5PubMed Central. Prevalence of small intestinal bacterial overgrowth in patients with gastroparesis: a systematic review and meta-analysis Other research using lactulose breath testing has reported even higher rates, with some studies finding that 60 to 70% of gastroparesis patients test positive.6American Journal of Gastroenterology. 3248 SIBO and Gastroparesis: Downstream Effects of Diabetes The spread between those numbers likely reflects different testing methods and patient populations, but the overall message is consistent: SIBO is extremely common when the stomach empties slowly.
SIBO matters for bowel habits because it independently causes diarrhea, bloating, and malabsorption. If you have gastroparesis and your bowel symptoms seem out of proportion to what you would expect, or if you develop new diarrhea or worsening bloating, SIBO is worth investigating. Treatment usually involves a course of antibiotics, though recurrence is common because the underlying slow motility that allowed the overgrowth in the first place has not changed.
Why So Many Gastroparesis Patients Also Have IBS
If you have gastroparesis and feel like your lower gut has a mind of its own, you are not imagining things. Studies consistently find that irritable bowel syndrome co-occurs at high rates. In one quality-of-life study using standardized diagnostic criteria, IBS coexisted in 64% of gastroparesis patients. Having IBS on top of gastroparesis was associated with significantly worse physical quality of life, and the combination added to the burden of nausea, pain, and medication use.7PubMed Central. Factors that Contribute to the Impairment of Quality of Life in Gastroparesis
In a separate propensity-matched comparison, IBS was found in about 24% of gastroparesis patients versus 27% of people with functional dyspepsia, a slightly lower rate. But chronic idiopathic constipation was more than twice as common in the gastroparesis group (about 10% versus 4%), and slow-transit constipation was also nearly twice as prevalent (roughly 8% versus 4%).3PubMed Central. Exploring Clinical Similarities and Distinctions Between Gastroparesis and Functional Dyspepsia: A Propensity‐Matched Cohort Study
The overlap makes clinical sense. The nerves and smooth muscle that control the stomach are part of the same enteric nervous system that governs the colon. When something goes wrong with gut motility, it rarely confines itself neatly to one organ. For patients, this means that “stomach” symptoms and “bowel” symptoms are often different expressions of the same underlying problem, not two separate conditions that happen to coexist by bad luck.
The Diabetes Connection
Diabetes is one of the most common causes of gastroparesis, and it brings its own set of bowel complications that layer on top. Long-standing, poorly controlled diabetes damages the enteric nervous system through a combination of oxidative stress, inflammation, and direct nerve injury. This damage affects not just gastric motility but also intestinal secretion, absorption, and colonic function, leading to what researchers describe as irregular bowel habits across the entire gastrointestinal tract.8PubMed Central. Enteric neuropathy in diabetes: Implications for gastrointestinal function
Diabetic autonomic neuropathy can produce chronic diarrhea, and in some cases fecal incontinence, as complications distinct from gastroparesis itself.9PubMed Central. Diabetic autonomic neuropathy of the gastrointestinal tract This creates a challenging clinical picture: a person with diabetic gastroparesis may have slow stomach emptying causing nausea and early fullness at the top of their digestive tract, while simultaneously having diarrhea or incontinence at the bottom, driven by nerve damage to the colon and rectum. The two problems can feel contradictory, and patients sometimes wonder if one of their diagnoses is wrong. Usually, both are real. They just reflect damage to different segments of the same nervous system.
SIBO rates may be especially high in diabetic gastroparesis. One proposed explanation is that diabetes impairs the migratory motor complex, the cyclical wave of contractions that sweeps through the small intestine between meals to clear out residual food and bacteria. When these waves are diminished or absent, bacteria accumulate, compounding the diarrhea and malabsorption that autonomic neuropathy is already causing.6American Journal of Gastroenterology. 3248 SIBO and Gastroparesis: Downstream Effects of Diabetes
Testing Beyond the Stomach
Standard gastroparesis workups focus on measuring gastric emptying, usually with a scintigraphy test where you eat a radiolabeled meal and a camera tracks how quickly it leaves the stomach. But as the research makes clear, knowing your stomach is slow does not tell you what your colon is doing. If bowel problems are a major part of the picture, additional testing can help.
One tool is the wireless motility capsule, a swallowable device that records pH, pressure, and temperature as it travels through the entire digestive tract. Because it moves through the stomach, small intestine, and colon in sequence, it provides transit time measurements for each region and for the whole gut in a single test.10PubMed Central. A technical review and clinical assessment of the wireless motility capsule This kind of information can be clinically useful because, as noted earlier, constipation severity in gastroparesis correlates with colonic and whole-gut transit times rather than with gastric retention itself.1PubMed Central. Constipation in Patients with Symptoms of Gastroparesis: Analysis of Symptoms and Gastrointestinal Transit Knowing whether your colon is also slow can change the treatment approach.
Radiopaque marker studies offer another way to evaluate colonic transit. You swallow a capsule containing small markers, then get X-rays a few days later to see how many markers have passed and where they are sitting. The study that found 65% slow-transit constipation in gastroparesis patients used this method.2Journal of Neurogastroenterology and Motility. High Prevalence of Slow Transit Constipation in Patients With Gastroparesis For patients stuck in a cycle of severe constipation that is not responding to laxatives, knowing that the colon itself has impaired motility can guide the choice of therapy and set more realistic expectations about what dietary changes alone can accomplish.
Managing Bowel Symptoms When Your Stomach Is Already the Problem
One of the trickiest aspects of gastroparesis is that the dietary advice for the stomach often clashes with what the bowel needs. Gastroparesis diets tend to emphasize low-fiber, low-fat, small-volume meals to reduce nausea and improve gastric emptying. But low fiber is the opposite of what a sluggish colon wants. Reducing fiber intake can worsen constipation that is already a problem for more than half of gastroparesis patients.
There is no single protocol that resolves this tension cleanly. Some patients find that soluble fiber supplements (which dissolve rather than adding bulk the way raw vegetables or bran would) are tolerable enough to help the colon without provoking stomach symptoms. Others need osmotic laxatives or prescription medications that target colonic motility directly. The key insight from the research is that constipation in gastroparesis is not merely a side effect of eating less; it reflects genuine motility impairment in the lower gut, and it may require its own treatment plan rather than being dismissed as a secondary nuisance.
For diarrhea, the approach depends on the cause. If SIBO is confirmed by breath testing, a course of targeted antibiotics can provide temporary relief, though many patients need repeated courses. If bile acid excess is suspected, bile acid sequestrants may help. If autonomic neuropathy is the driver, antidiarrheal medications and careful attention to blood sugar control are the usual strategy, since nerve damage progresses more slowly when glucose levels are better managed.
Pelvic Floor Problems in Gastroparesis
A dimension that often gets overlooked is the pelvic floor. The study that evaluated gastroparesis patients with anorectal testing found significantly higher rates of structural pelvic floor issues. About 89% of gastroparesis patients had rectocele (a bulging of the rectal wall), compared to 60% of people with normal gastric emptying. Intussusception, where part of the rectal wall telescopes into itself during straining, was present in roughly 44% of the gastroparesis group versus 12% of controls.2Journal of Neurogastroenterology and Motility. High Prevalence of Slow Transit Constipation in Patients With Gastroparesis
These structural changes matter because they affect how effectively you can evacuate stool even when the colon manages to move things along. Chronic straining from slow-transit constipation likely contributes to these problems over time. Interestingly, the rate of dyssynergic defecation, where the pelvic floor muscles contract when they should be relaxing, was almost identical between gastroparesis patients and controls (about 41-42% in both groups). So the coordination issue is common across the board, but the structural damage is disproportionately concentrated in people with gastroparesis.
Pelvic floor physical therapy, which involves retraining the muscles involved in defecation, can help with both dyssynergia and the functional consequences of structural changes like rectocele. It is underutilized in gastroparesis care, partly because the focus tends to stay on the stomach. If you are doing everything right for your constipation and still struggling to evacuate, a pelvic floor evaluation is worth pursuing.
Why Women May Experience Worse Symptoms
Women are disproportionately affected by gastroparesis. While the exact reasons are still being worked out, research points to the role of sex hormones in regulating a key enzyme called neuronal nitric oxide synthase, which produces nitric oxide, a molecule that helps smooth muscle in the gut relax. Impairment of this system is considered one of the main factors in gastroparesis, and sex hormones appear to influence how well it functions.11PubMed Central. Gender bias in gastroparesis: is nitric oxide the answer?
This has implications for bowel habits as well. If the same smooth-muscle relaxation pathway is compromised throughout the gut and not just in the stomach, it helps explain why whole-gut dysmotility, including constipation, slow colonic transit, and pelvic floor problems, tends to cluster in the same patients. Hormonal fluctuations across the menstrual cycle can also independently affect gut motility, meaning that women with gastroparesis may notice their bowel symptoms shift predictably with their cycle, getting worse in the luteal phase and somewhat better after menstruation. This is not unique to gastroparesis, but it is more pronounced when baseline motility is already impaired.