Research suggests a potential connection between autism and irritable bowel syndrome (IBS). Studies have shown that digestive symptoms are more common in autistic individuals than in neurotypical people.

IBS refers to a group of symptoms including diarrhea, constipation, cramping, and bloating. People with IBS may experience these symptoms in response to certain foods, stress, or other triggers.

While research has shown these symptoms are more common in autistic people, it is unclear what the link is, or whether IBS is the cause in all cases.

This article looks at the prevalence of IBS in autistic people, possible connections between IBS and autism, and how the symptoms may affect them. It also discusses the signs of IBS, IBS treatments, and whether probiotics and diet affect autism.

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According to a 2022 review, various studies have found that digestive symptoms, such as diarrhea, abdominal pain, and constipation, are common in autistic children and adolescents.

Although these symptoms are typical of IBS, the research often discusses digestive issues and gut health in more general terms and does not always link them to IBS specifically.

The authors found that the symptoms were more prevalent in autistic people than in neurotypical individuals.

Another 2021 research article states that between 46% and 84% of autistic children have gastrointestinal symptoms or disorders, including:

Scientists have several theories for why digestive symptoms may be more prevalent in autistic people.

The gut-brain axis

The gut-brain axis refers to the complex two-way communication system between the digestive tract and the brain.

The communication system relies on various components, including elements of the immune system, certain neurotransmitters and neural pathways, and the gut microbiota.

The gut microbiota are the trillions of bacteria and other microorganisms in the GI tract that affect various bodily and neurological functions.

A 2020 review of past research notes there is evidence of differences between the gut microbiota in autistic people and neurotypical people. These differences may contribute to IBS-like symptoms, which, in turn, could potentially intensify autism symptoms by causing distress.

Possible microbiota differences in autistic people include the following:

  • higher levels of the fungus candida albicans, which may affect the body’s ability to absorb minerals and carbohydrates
  • lower-than-usual levels of Prevotella, a bacterium that encourages gut health
  • lower levels of lactobacillus, a type of bacteria that helps the gut break down food and resist infection
  • higher levels of the bacteria Clostridium, which may lead to various GI symptoms

It is important to note that these findings do not mean that microbiome disturbances cause autism. More research is necessary to understand the causes.

Eating habits

Many autistic people experience sensory hypersensitivity, which means that certain textures, flavors, or smells may be distressing to them.

Sensory difficulties may lead to a person eating a restricted diet, which could influence gut health. They may not get enough fiber, which could lead to constipation, or they may develop dysbiosis, which is an imbalance of gut flora.

Mental health

Past research suggests that mental health conditions affect 70% of autistic people. The most common of these is anxiety, which is especially prevalent in autistic children.

Researchers believe autistic children may be more reactive to stress than neurotypical children. Anxiety and stress can be potential triggers for IBS.

Additionally, a systematic review found that people who have traumatic experiences are more likely to develop IBS. Autistic people are more likely to experience trauma than those who are not autistic.

Genetics

A 2024 study found genetic associations between IBS and autism, as well as multisite pain and fatigue. The authors theorize that this association may explain why these things often occur together, as they may have shared genetic roots.

However, the authors also say this association may partly explain the association. The study did not establish if one directly causes the other, so more research is necessary to understand how genes play a role.

IBS and other digestive issues can cause stress, and in autistic people, they may feel overwhelming to the senses.

This may cause more pronounced autism symptoms, particularly in people who have difficulty communicating their symptoms to others.

A 2020 review notes that digestive symptoms in autistic children may lead to:

The symptoms, or their knock-on effects, may also reduce quality of life or lead to other complications.

The signs of IBS typically include recurring abdominal pain, diarrhea, and constipation.

However, if a person has difficulty discussing these symptoms with others, loved ones may not be aware of them. In these cases, the signs of a health condition may manifest through changes in behavior or emotions.

  • increased or unusual vocalizations, such as frequent swallowing or moaning
  • increased irritability or aggression
  • movements such as tapping or grimacing
  • anxiety

Some autistic children also have pica, which is the ingestion of non-edible items. Pica has an association with IBS and constipation, although scientists currently do not know if pica causes the digestive symptoms, or vice versa.

The treatments for IBS or other digestive symptoms are the same for autistic people as those who are not autistic. Often, it involves a combination of lifestyle or dietary changes and medications.

There is no single cure for IBS, but there are things that can reduce the symptoms. A doctor should tailor recommendations to a person’s symptoms and needs.

  • Drinking enough fluids: Drinking plenty of water and non-caffeinated drinks throughout the day can help prevent constipation.
  • Reducing stress: Stress may contribute to digestive symptoms. Strategies and resources that help reduce stress may also help relieve these symptoms.
  • Eating a balanced diet: Some autistic people with sensory issues may find it difficult to eat a wide range of foods. If this is the case, they may want to consult a nutritionist or dietitian who has experience working with autistic people to ensure they get enough nutrients and fiber.
  • Identifying triggers: For some, specific foods or drinks trigger digestive symptoms. A dietitian can also help identify items that may be causing problems and find healthy ways to avoid or replace them.
  • Taking medications: Medications such as loperamide (Imodium) can help treat diarrhea, while others may help to reduce constipation or pain.
  • Treating coexisting conditions: Sometimes, digestive conditions result from an underlying problem, such as mental health conditions, structural differences in the digestive system, or eating disorders. A doctor may be able to help identify and treat any coexisting conditions.
  • Trying probiotics: Probiotics may improve gut symptoms for some people. However, there is still much scientists do not know about probiotics and the microbiome. Probiotics can also cause side effects.

Some may find making changes to routines difficult. Additional support from health professionals with experience working with autistic people may help.

There is no evidence that any diet, probiotic, or other approach can cure or prevent autism.

However, some may find that these approaches reduce digestive symptoms, which could reduce distress or affect behavior. Below is some of the scientific evidence.

Probiotics

A 2020 review notes that there have been some small trials with probiotics in autistic people. While some found positive results, not all participants experienced improvements in digestive symptoms or behavioral challenges. In one trial, quality of life also did not significantly improve.

Diet

A 2023 study surveyed 818 people to determine how diet may affect their symptoms. The study examined 13 different diets, including gluten-free, ketogenic, paleo, and sugar-free diets.

Participants rated a healthy diet and the Feingold diet as having the most overall benefit. The Feingold diet involves avoiding certain food additives.

However, this study has some limitations. While it had many participants, it relied on self-reported observations from both autistic individuals and parents or caregivers of autistic children.

There is also the potential for the placebo effect or response bias to affect the results. Response bias occurs when people who experienced perceived benefits from a treatment respond to surveys more than those who felt no improvement, skewing the results.

There are no studies proving that the Feingold diet helps reduce autism.

Research shows that autistic people are more likely to have digestive problems than neurotypical people, including IBS.

Factors that may explain why there is a higher prevalence of these symptoms in autistic people include changes in the microbiome, dietary restriction, coexisting conditions, and genetics. However, scientists are still not sure exactly what causes it.

A healthcare professional with experience treating autistic individuals may be able to help diagnose and treat IBS or other digestive symptoms. Treatment may involve dietary changes, medication, and stress reduction strategies.