Studies indicate that many things may lead to the development of irritable bowel syndrome (IBS) and chronic fatigue syndrome (CFS). Researchers who look at factors the conditions share — including fatigue, pain, and in many instances, gut dysfunction — have come up with several theories based on scientific evidence that could explain why they often coexist: among them are infection, immune problems, and heightened pain perception. But scientists have yet to pinpoint one common denominator. “These are complex conditions — that’s why it’s so hard to say that there is one blood [test] or other type of medical test that’s going to diagnose these syndromes," says Lin Chang, MD, the director of the digestive health and nutrition clinic and a professor of medicine at the David Geffen School of Medicine at the University of California in Los Angeles. “They are both multifactorial.”

Symptoms and Diagnosis of the 2 Conditions 

With IBS, your bowels stop working the way they should, causing abdominal pain and a change in bowel habits — like diarrhea, constipation, or both. To get a diagnosis, you must experience abdominal pain at least three times a month for three months. IBS is called a functional bowel disorder, meaning there’s no known anatomical problem in the intestines, as with cancer or colitis. With chronic fatigue syndrome, you’re more than just tired. You have an unexplained, persistent fatigue that lasts for at least six months and isn’t helped by rest. Since there’s no test to diagnose it, doctors rely on symptoms to make a determination. Aside from fatigue, you also need to exhibit at least four of the following symptoms to be diagnosed with chronic fatigue:

Feeling unwell for more than a day after physical activityMuscle painHeadachesMemory problemsJoint painSleep disturbancesSore throatTender lymph nodes

These symptoms can resemble those of other diseases or conditions, so first your doctor will need to rule out other causes before making a definitive diagnosis of CFS. Some people with chronic fatigue can carry on life with some limitations, but about 25 percent are fully disabled by the condition, according to the National Fibromyalgia & Chronic Pain Association. It’s also important to note that both chronic fatigue syndrome and IBS are diagnosed more often in women than men in the United States.

6 Possible Ways the Conditions Are Connected

So, what’s the connection between the two conditions? Dr. Chang says that many factors may contribute to the development of both conditions. Here are some possible scenarios.

  1. Post-infectious syndromes IBS sometimes develops after a stomach bug or food poisoning, says Chang. Likewise, chronic fatigue syndrome has been seen in people after a bacterial, viral, or parasitic infection. “In fact, in chronic fatigue, one of the biggest theories is that some sort of infection is causing the symptoms,” she says. Studies from Norway have linked Giardia infection, or giardiasis, with both the development of IBS and CFS. The most recent study, published in 2018 in the journal Clinical Gastroenterology and Hepatology, tracked what happened after the parasite got into the water supply in Bergen, Norway, in 2004. In total, more than 1,200 exposed patients had confirmed giardiasis, causing diarrhea, stomach pain, and other intestinal problems, that was traced back to the outbreak. The long-term study followed nearly 600 individuals who recovered from the infection and compared their health with people who had not been infected. At the 10-year mark, 43 percent of the exposed individuals had developed IBS, compared with just 14 percent of those who had not been affected. CFS was reported in 26 percent of the infected group, compared with 11 percent of the others.
  2. Overactive immune response In IBS, scientists theorize that an immune response in the gut could trigger changes in secretions or the way the bowel moves or senses pain, causing symptoms, says Chang. In CFS, she says, a problem in the immune system may cause production of inflammatory substances that are linked to fatigue.
  3. An imbalance in gut bacteria Research suggests that people with CFS may have abnormal levels of certain gut bacteria. A study published in 2017 in the journal Microbiome found that people with chronic fatigue syndrome had higher levels of specific gut bacteria and lower levels of others compared with the gut bacteria of individuals without the condition. The researchers then checked to see if these imbalances were shared by patients who also had IBS. The results showed that participants did indeed have different patterns of gut bacteria abnormalities depending on whether they had both conditions or chronic fatigue syndrome alone. While the relationship between gut bacteria levels and chronic fatigue syndrome is not well understood, some researchers hypothesize that these disturbances may play a role in causing the condition. RELATED: Gut Bacteria May Influence Whether You’re Successful on a Diet
  4. Enhanced pain perception People with IBS and possibly those with chronic fatigue syndrome tend to process pain differently from people without the conditions. Chang explains it this way: “Say I have IBS or another chronic pain condition and you don’t, and someone applies intense pressure to our thumbnails. At the same [applied] pressure, I’ll feel it as a much more intense pain. I will rate it as 8 out of 10, and you’ll rate it as 2 out of 10. The pressure threshold that I feel pain will be lower than yours.” In IBS, the increased sensitivity occurs mainly in the bowels.
  5. Genetic predisposition Researchers are also looking at whether gene variations make people more vulnerable to getting IBS, chronic fatigue, or another functional syndrome. Environmental factors including stress may contribute to the development of these conditions or trigger a flare, Chang says. “It’s possible that the combination of chronic stress and a certain genetic type would predispose an individual to getting IBS and chronic fatigue syndrome,” she adds.

Treating Chronic Fatigue Syndrome and IBS

When IBS and chronic fatigue overlap, you may face a unique set of challenges. “You have to treat multiple symptoms, and patients have a harder time managing their symptoms because it’s overwhelming sometimes,” says Chang. In addition to specific symptom treatments, Chang uses interventions that she says are useful for both conditions:

Cognitive behavioral therapy Talk therapy can give you tools to manage your condition, provide you some sense of control, and help you feel less overwhelmed.Medications that reduce pain Talk to your doctor about what medications may help reduce the pain from both conditions.Lifestyle changes Having routine activities and daily structure and not overexerting yourself can help ease symptoms of both IBS and chronic fatigue.

Chang adds that improving mood and sleep will go a long way toward improving both conditions, as well.