Study: Gastrointestinal Symptoms Correlate with Autism Severity


  It has long been known by parents (and many health professionals), that children with autism have higher prevalence of gastrointestinal (GI) issues. Ask any parent of a child with autism, and they will likely tell you that their child has gastrointestinal symptoms: diarrhea, constipation, gas/bloating, or pain.

Regrettably, digestive symptoms like diarrhea, constipation, and bloating are often ignored or considered an aspect of a child’s “autism.” This suggests that somehow diarrhea and other potty accidents are a “behavior,” and result of autism. This is preposterous.

After years of study, research is confirming that GI problems are higher in children with autism (see chart below).boy_tummyache_iStock_000014831124XSmall A research study in the journal BMC Gastroenterology, explored not only “if” children with autism are different, but “how.” In this study, “Gastrointestinal flora and gastrointestinal status in children with autism–comparisons to typical children and correlation with autism severity,” Dr. Jim Adams, found differences between the children with autism and controls, and also found that GI distress appears to play a role in autism symptoms.[1] The study concluded, “The strong correlation of gastrointestinal symptoms with autism severity indicates that children with more severe autism are likely to have more severe gastrointestinal symptoms and vice versa.” Before we go into more about what the research found, I have put the summary of studies Adams, et al. outlines in the “Background” section into a chart to layout the research that identifies an increase of GI problems in children with autism. Children with Autism Have Increased Rates of GI Distress NH Blog - Table Adams, et al. in BMC Gastroenterology You can see that there are many studies showing an increase in digestive disturbances with children with autism. Back to the study itself and the findings.  Children with autism had:
  • Beneficial Bacteria: The children with ASD had much lower levels of bifidobacterium and much higher levels of lactobacillus.
  • Inflammation: The only marker that showed a significant difference was lower level of lysozyme in the autism group.  “A marker consistent with bacterial, viral, allergenic, and autoimmune caused bowel inflammation.” The researchers suggest “possibly associated with probiotic use.”
  • Short Chain Fatty Acids: There was a significantly lower amount of SCFA as a total, as well as lower levels of acetate, proprionate, and valerate in the group with autism.  It was suggested to be due in part by probiotic use (as the children with autism taking probiotics had the greatest lowest SCFA values), as well as lower intake of fiber, and other reasons.
In the study they also evaluated the effects of probiotics and fish oil.  Here are some interesting results. Effect of Probiotics: The autism group was divided into those that took probiotics daily and no-probiotic (those that did not use any).  Interestingly, probiotics did not have a significant effect on most of the beneficial bacteria, except for a marginally higher level of lactobacillus in those that took probiotics everyday. The probiotic group had lower lysozyme level but not significantly. Effect of Seafood and Fish oil consumption: In this case, the autism group was divided into three groups: “fish” group (that consumed fish more than 2x/month and 57% consumed fish oil daily), the “fish oil” group (no fish but daily fish oil supplementation), “no fish” (no fish or fish oil). The “fish” group had “dramatically” lower levels of lactobacillus. The “Fish Oil” group had slightly higher pH. The rest of the markers showed no significant difference: dysbiotic bacteria, yeast, elastase, presence of fat, muscle fibers, vegetable fibers, and monosaccharides, other inflammatory markers (except lysozyme), secretory IgA, RBC and fecal pH. One of the biggest surprises was finding no significant increase in yeast in the autism group, since so many children with autism appear to have yeast (and respond positively to antifungals).  I wonder if this is because the method of testing used (stool vs. urine), or if the improvement many see with antifungals is due to something other than reducing yeast.  Although I do believe children with autism have yeast, and we may find an increase in yeast in another study or subgroup of autism. Another interesting observation was that probiotics did not make a significant difference in the levels of probiotic colonizing in the gut (except a marginal increase in lactobacillus)—this is especially true for bidifobacteria levels which was significantly lower in autism than controls and not raised by probiotics.  While this was disappointing, it is something I have seen clinically with a number of clients—supplementation with probiotics did not raise their probiotic levels.  While unsure of the reason for this (or if there is something else at play), I wonder if this is true of probiotics for some people and whether fermented foods would be more helpful in colonizing and raising levels of beneficial bacteria. To summarize the study of Adams, et al., they found many GI differences in children with autism vs controls. This study was not designed to test the percentage of children with autism with GI problems vs controls – because the control group was chosen because they do not have digestive problems. This study was designed to identify functional differences in GI flora and status.   There were lower levels of beneficial bacteria, lysozyme, and short chain fatty acids.  Most interestingly and importantly, there was a strong correlation of gastrointestinal symptoms with autism severity. Studies such as these are so valuable for the autism community.  These studies provide answers to what is underlying the physiology of children with autism and resulting symptoms. Most importantly as a nutritionist, we see that children with autism have GI differences and dysfunction—and diet is essential to address when you have GI distress!  The food we choose has a significant effect on the inflammation (or lack of inflammation) in the gut.  This food also supplies needed nutrients that are often in short supply and poorly absorbed.  As such, we want to avoid foods that contribute to inflammation, and consume foods that are high in nutrients and those easily digested.
  1. Adams, J. B., Johansen, L. J., Powell, L. D., Quig, D., & Rubin, R. A. (2011). Gastrointestinal flora and gastrointestinal status in children with autism–comparisons to typical children and correlation with autism severity. BMC gastroenterology, 11(1), 22.
  2. Molloy CA, Manning-Courtney P: Prevalence of chronic gastrointestinal symptoms in children with autism and autistic spectrum disorders. Autism 2003, 7(2):165-171.
  3. Nikolov Roumen N, Bearss Karen E, Jelle Lettinga, Craig Erickson,
Maria Rodowski, Aman Michael G, McCracken James T, McDougle Christopher J, Elaine Tierney, Benedetto Vitiello, Eugene LArnold,
Bhavik Shah, Posey David J, Louise Ritz, Lawrence Scahill: Gastrointestinal Symptoms in a Sample of Children with Pervasive Developmental Disorders. J Autism Dev Disord 2009, 39:405-413.
  4. Xue Ming, Michael Brimacombe, Janti Chaaban, Barbie Zimmerman-Bier, Wagner George C: Autism Spectrum Disorders: Concurrent Clinical Disorders. J Child Neurol 2008, 23(1):6-13.
  5. Valicenti-McDermott M, McVicar K, Rapin I, Wershil BK, Cohen H, Shinnar S: Frequency of gastrointestinal symptoms in children with autistic spectrum disorders and association with family history of autoimmune disease. J Dev Behav Pediatr 2006, 27(2 Suppl):S128-36.
  6. Adams JB, Holloway CE, George F, Quig D: Analyses of Toxic Metals and Essential Minerals in the Hair of Arizona Children with Autism and their mothers. Biol Tr El Res 2006, 110:193-209.

Julie Matthews is a Certified Nutrition Consultant who received her master’s degree in medical nutrition with distinction from Arizona State University. She is also a published nutrition researcher and has specialized in complex neurological conditions, particularly autism spectrum disorders and ADHD for over 20 years. Julie is the award winning author of Nourishing Hope for Autism, co-author of a study proving the efficacy of nutrition and dietary intervention for autism published in the peer-reviewed journal, Nutrients, and also the founder of Download her free guide, 12 Nutrition Steps to Better Health, Learning, and Behavior.


  1. If this was all that is causing it then there shouldn’t be any kids left with autism. The fact that some kids have a hard time eating in the first place is very alarming. I just think the truth is not being told, and we are being told more excuses. How can anyone keep looking at this, and not think something is terribly wrong considering how many kids keep being affected by autism is beyond me.

  2. Dr Bradstreet has written about how probiotics “like” an aerobic environment, rather than an anaerobic environment, such as the small and large intestines. So, from what he has stated about probiotics, I am not surprised at the results about probiotic use.

    Thank you for this article. There are certain GI MDs in my area that need to read it. My son was not offered an EGD by an MD at Children’s Memorial in Chicago b/c of his “autism” diagnosis. My son has severe oral aversions. Once I took him to Dr. Arthur Krigsman, my son finally had a full scope done of his GI tract, and we got some answers. (EE and Crohn’s like ileitis.)

    I hope that many autism parents will bring this article to pediatric GI MDs who blame GI issues on behavioral components of autism. Our kids have physical problems in their GI tracts.

    • Correction: only the large intestine is an anaerobic environment.

  3. “Regrettably, digestive symptoms like diarrhea, constipation, and bloating are often ignored or considered an aspect of a child’s “autism.” This suggests that somehow diarrhea and other potty accidents are a “behavior,” and result of autism. This is preposterous.”

    Well, it’s preposterous with the assumptions you make. 🙂 I completely agree that diarrhea/constipation/potty accidents are not behavioural. But I disagree about it being a result of the autism. Autism is not a behavioural issue. It’s not psychological. Behaviours AND the potty problems are both the result of the autism, which is a neurological issue.

    • Hi Luna,

      I agree. Originally, I had written something similar explaining that if you see “autism” as neurological – it is a result of autism. I decided to simplify it for the purposes of this article. Next time, I’ll explain that point as well. Thanks for the feedback.

    • If it’s neurological, then why did a neurologist not know a thing about my son’s aspergers? No clue how to diagnose it. I went to a children’s behavioral specialist to get his diagnosis. Shouldn’t a neurologist know about all branches of autism? Including aspergers?


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