The gut microbiome and its role in ulcerative colitis

Your gut is home to trillions of bacteria and other tiny living organisms. These microorganisms, also called microbes, make up your gut microbiome. A growing body of research is shedding light on the important role the gut microbiome plays in human health and disease.

Studies show that changes in the gut microbiome are common in people who have ulcerative colitis (UC). These changes may influence inflammation and how the condition behaves over time.

Here are some things to know about the gut microbiome, how it relates to ulcerative colitis, and which diet and lifestyle choices support the community of organisms living in your gut.

The gut microbiome is made up of bacteria, viruses and fungi that live in the gastrointestinal (GI) tract. Most of these microorganisms live in the large intestine, also called the colon. There are about 1,000 different species of bacteria that live in the GI tract, and they make up the majority of microbes in the gut microbiome.

The bacteria in the gut are helpful in many ways, including:

• Breaking down parts of food that your body cannot digest on its own.
• Producing vitamins and short‑chain fatty acids (SCFAs), which help regulate inflammation and support the immune system.
• Supporting the protective lining of the intestines, which helps prevent harmful germs and toxins from triggering inflammation.

Studies show that people with ulcerative colitis (UC) often have a condition called dysbiosis, which means the mix of microbes in the gut is out of balance. This can include too few helpful bacteria, too many potentially harmful bacteria and a lower variety of microbes

When the gut microbiome is out of balance, microbes may produce fewer short‑chain fatty acids and other helpful substances that support a healthy intestinal lining. These changes can affect how the immune system responds and may increase inflammation, especially in conditions like ulcerative colitis.

There's no evidence that changes in the gut microbiome alone cause ulcerative colitis.

The exact cause of UC isn't known. Research suggests that the condition develops from a combination of factors, which may include dysbiosis of the gut microbiome, certain genes, how the immune system responds, weakness or damage to the lining of the colon, diet, a history of smoking, or using certain medicines.

Research shows that inflammation can alter the gut microbiome and that changes in the microbiome can increase inflammation. But researchers don't yet fully understand how this cycle begins or what role it plays in developing ulcerative colitis.

Microbiome‑based treatments are currently limited to clinical trials. Promising research is underway, but results are not consistent.

One therapy being studied as a possible treatment for ulcerative colitis is fecal microbiota transplantation (FMT). This involves transferring processed stool from a donor into a recipient's gut to restore balance to the gut microbiome.

Clinical trials show that FMT may help treat ulcerative colitis for some people, but results vary. Many factors can influence how well the procedure works, including donor selection, how the stool is prepared and delivered, the severity of disease, and a person's overall health, diet and lifestyle. Because of these uncertainties, FMT is considered experimental for ulcerative colitis and is offered only through clinical trials.

The foods you eat strongly influence the microbes living in your gut. Diets high in sugar, salt or fat, highly processed or fast foods, or alcohol are linked to fewer beneficial bacteria and less diversity in the gut microbiome. Over time, these patterns may reduce the production of short‑chain fatty acids (SCFAs) and other substances that support a healthy gut lining and help regulate inflammation.

In contrast, diets rich in fruits, vegetables and fiber help nourish beneficial gut bacteria. Gut bacteria use parts of your diet — especially fiber — as a source of energy. Fiber isn't digested in the small intestine, so it reaches the colon, where bacteria break it down. During this process, bacteria produce SCFAs, vitamins and other helpful compounds.

Short‑chain fatty acids are important for people with ulcerative colitis because they:

• Are a main energy source for cells in the colon.
• Help calm inflammation.
• Support and strengthen the gut barrier.

Some people with ulcerative colitis (UC) can't tolerate eating much, if any, fiber — especially during a flare-up. The goal isn't to eat as much fiber as possible, but to find ways to support the microbes living in your gut that your digestive system can tolerate.

If your healthcare professional recommends a low‑fiber or low‑residue diet, you still have options to support your microbiome and overall nutrition.

Change the texture. Instead of raw fruits and vegetables, try steaming, baking, blending, roasting or grilling produce. This makes them easier to digest.

Choose soluble fiber foods. Soluble fiber is often less irritating than insoluble fiber for some people. Examples include oatmeal, sweet potatoes without skin, bananas and cooked carrots. Some people may tolerate small amounts of ground flax.

Try resistant starch. Resistant starch is a type of carbohydrate that feeds gut microbes. Examples include slightly green bananas and cooked‑then‑cooled oatmeal, rice and potatoes. These foods can be reheated before eating.

Consider fermented foods. Some fermented foods contain beneficial bacteria that support the gut microbiome. Examples include yogurt, kefir and sauerkraut. Look for labels that say "live and active cultures" or "live probiotics." If dairy worsens symptoms, lactose‑free versions may be an option.

Fermented foods stored in the refrigerator are more likely to contain live microbes. Shelf‑stable canned or jarred products are often pasteurized, which removes live cultures.

Be cautious with probiotic supplements. Many people assume probiotic supplements will fix the gut microbiome, but evidence is mixed. The American Gastroenterological Association does not recommend probiotic supplements for treating ulcerative colitis in most situations. This doesn't mean they never help, but they should be treated like medicine and discussed with your healthcare professional before use.

Research shows that daily habits can support or disrupt the gut microbiome.

Sleep. Poor or irregular sleep can alter gut bacteria and may make the GI tract more sensitive.

Stress and emotional well‑being. Stress hormones can change how quickly or slowly food moves through the digestive tract and how well the lining of the intestine functions. These changes can affect the gut microbiome. Managing stress can help support a more stable gut environment.

Physical activity. Regular movement is linked to a more diverse microbiome and bacteria that produce helpful substances. Even gentle activity can help over time.

Smoking and vaping. Tobacco exposure is linked to changes in gut bacteria and increased inflammation.

Alcohol. Limiting alcohol can help support a healthy gut lining and more stable gut microbiome.

Antibiotics. Antibiotics are sometimes necessary for treating UC, but they also can reduce helpful bacteria. Use antibiotics only when needed and under the guidance of your healthcare team.

The tiny microbes living in your gut are your partners in health and wellness. Talk with your care team about the food and lifestyle choices that will support the gut microbiome to help you feel your best.