Every time someone purchases a hamburger, there’s a chance that they’re exposing themselves to a chemical which might cause or exacerbate autism—and major food companies like McDonald’s are scrambling to pull it from their products. The chemical is calcium propionate, and a growing body of literature suggests that limiting exposure is critical to protecting health.
Calcium propionate is widely used in the food industry as an edible preservative and antifungal agent; products such as fruit, packed meat, cheese, and bread are routinely sprayed with heavily diluted calcium propionate to prevent mold from taking root and causing spoilage. While the chemical is effective in its antifungal role, research suggests that calcium propionate may contribute to the development and exacerbation of autism spectrum disorder (ASD) due to its impact on the gut microbiome. As a result of the relationship between calcium propionate and autism, many consumers are now seeking to avoid products containing the preservative, and food producers are reformulating their offerings in response to this changing demand. However, simply limiting intake of calcium propionate might not be enough to restore gut health and prevent damage. Instead, those seeking to minimize or eliminate calcium propionate exposure should simultaneously support the body’s natural gastrointestinal defenses through butyric acid supplementation.
The Origin and Potential Danger of Calcium Propionate
In the body, propionic acid is not used primarily for its antifungal properties. Instead, it is a precursor to other biological chemicals like succinyl-CoA, which cells use to break down stored energy and prepare it for immediate use. The rate of propionic acid metabolism is affected by a plethora of genetic, microbiotic, and environmental factors, and the majority of people have more than enough of the chemical to support their bodily processes. However, having an overabundance of propionic acid may be a problem—especially for patients with ASD.
In the laboratory, researchers have found that infusions of propionic acid into brain tissue of mice causes the mice to develop behavioral symptoms which are consistent with autism spectrum disorder. These behavioral symptoms include reduced propensity to socialize, repetitive motions, abnormal interests in food objects, and perseveration of ineffective actions. Increasing the dose of propionic acid increases the intensity of these symptoms, meaning that additional consumption of propionic acid might do the same to people who have ASD.
Patients with ASD are prone to having excess propionic acid due to ASD-related microbiome abnormalities and highly restricted diets, make them uniquely vulnerable to further damage. However, healthy people may also be affected; while they may not become debilitated by excess exposure to propionic acid, such exposure could cause mild ASD-like symptoms that they would not experience otherwise. These symptoms might not be easy to detect and they should dissipate quickly as propionic acid is cleared from the body. However, lasting damage might be occurring as a result of the acid’s impact on the microbiome and the brain.
Exploring the Relationship Between Propionic Acid and Autism
The gut is the site of most propionic acid synthesis because it is where bacterial colonies of the microbiome consume dietary fiber and secrete propionic acid or other similar chemicals. Under ideal conditions, the many different species of bacteria that compose the gut microbiome have population sizes within a narrow range of proportions; having a disproportionate amount of one species of bacteria may be harmful and leads to starvation of another species. Additionally, having too many of one species may lead to excessive production of the chemical that the species contributes upon digesting fiber.
Deviations in the proportion of species can occur for a handful of different reasons, one of which is higher consumption of external nutrients which favor certain bacteria over others. When detrimental bacteria are favored, the immune system responds with inflammation in an effort to remove them. This inflammation contributes to the gastrointestinal problems associated with ASD while also harming beneficial gut microbiota. Furthermore, inflammation caused by the immune system stimulates the gut-brain axis, which can cause behavioral and psychological disturbances, such as anxiety.
Excess propionic acid can cause significant disruptions of the microbiome because propionic acid signals the immune system of the gut to activate and cause inflammation. This inflammation can subsequently harm beneficial bacteria which secrete butyric acid—a highly versatile short-chain fatty acid with multiple critical functions—more than it harms the bacteria secreting propionic acid. Under normal conditions, the inflammation resolves itself. However, in patients with ASD, the conditions of the gut are more variable and require special control. As such, bacteria responsible for producing butyric acid are suppressed while the bacteria which produce propionic acid become widespread. This causes a further exacerbation of the patient’s gastrointestinal symptoms because butyric acid is responsible for signaling the immune system to reduce inflammation in the gut. Furthermore, the non-immune systems of the gut can’t function effectively because they’re forced to use propionic acid, which is an inferior energy source that cells can’t process as efficiently as butyric acid. Propionic acid subsequently accumulates in the gut and elsewhere, inducing more inflammation and further aggravating ASD symptoms.
In addition to increasing severity of ASD symptoms, propionic acid may also have a causative relationship with the development of the disorder due to its direct neurological impact. Both propionic acid and butyric acid readily cross the blood-brain barrier and are used by neurons as an energy source, with especially heavy usage occurring during early fetal development. Due to the acute sensitivity of the brain at this time, researchers believe that excess propionic acid exposure in early pregnancy may be one of the factors which contribute to the development of ASD. This means that pregnant women should avoid consuming foods which are known to be treated with calcium propionate. If consuming them is necessary, an acceptable alternative is to wash the foods to remove as much of the chemical as possible. Additionally, although there are no studies documenting newborns or infants acquiring ASD as a result of propionic acid, excess exposure may cause invisible damage nonetheless. In the brain, propionic acid is a second-class energy source, just as it is in the gastrointestinal tract. Concentrations of propionic acid can thus grow, eventually causing the cellular dysfunction which is associated with ASD symptoms.
Taking Action to Reduce the Impact of Calcium Propionate
One of the most promising ways to support gut health is via butyric acid supplementation. Of particular note are advanced formulations such as AuRx from Tesseract Medical Research, which is specifically designed to restore the microbiome of patients with ASD and can create a greater level of symptom remission than removing dietary calcium propionate intake alone. Critically, supplemental butyric acid provides the cells of the gut and the brain with their preferred energy source, potentially alleviating inflammation, easing gastrointestinal distress, and supporting healthy neurological function. As a result, the patient’s microbiome can take time to recover without prolonged exacerbation of ASD symptoms; while extant propionic acid may remain in the patient’s gastrointestinal tract, providing the cells with butyric acid via supplementation gives them enough additional energy that they may be able to clear the excess propionic acid without leaving the patient to suffer in the meantime.
Thanks to the innovative repurposing of butyric acid as a therapy, ASD patients now have an invaluable resource to help them recover from destabilizing factors like calcium propionate. Additionally, by promoting the balanced growth of microbiota, the gut is better able to cope with future deviations of pH which may result from diet. Strategically integrating high-quality butyric acid supplements may thus be a critical component of ongoing ASD management.
Adams JB, Johansen LJ, Powell LD, Quig D, and Rubin RA. 2011. Gastrointestinal flora and gastrointestinal status in children with autism — comparisons to typical children and correlation with autism severity. BMC Gastroenterology. 11:22. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3072352/
Biggs AR, El-Kholi MM, El-Neshawy S, and Nickerson R. 1997. Effects of calcium salts on growth, polygalacturonase activity, and infection of peach fruit by monilinia fructicola. Plant Disease. 81(4):399-403. https://apsjournals.apsnet.org/doi/10.1094/PDIS.1918.104.22.1689
Den Besten G, van Eunen K, Groen AK, Venema K, Reijngoud DJ, et al. 2013. The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism. Journal of Lipid Research. 54(9):2325-2340. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3735932/
Frye RE, Nankova B, Bhattacharyya S, Rose S, Bennuri SC, et al. 2017. Modulation of immunological pathways in autistic and neurotypical lymphoblastoid cell lines by the enteric microbiome metabolite propionic acid. Frontiers in Immunology. https://www.frontiersin.org/articles/10.3389/fimmu.2017.01670/full
MacFabe DF, Cain DP, Rodriguez-Capote K, Franklin AE, Hoffman JE, et al. 2007. Neurobiological effects of intraventricular propionic acid in rats: Possible role of short chain fatty acids on the pathogenesis and characteristics of autism spectrum disorders. Behavioral Brain Research. 176(1):149-169. https://www.sciencedirect.com/science/article/pii/S0166432806004165?via%3Dihub
Thomas RH, Foley KA, Mepham JR, Tichenoff LJ, Possmayer F, et al. 2010. Altered brain phospholipid and acylcarnitine profiles in propionic acid infused rodents: further development of a potential model of autism spectrum disorders. Journal of Neurochemistry. 113(2):515-529. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1471-4159.2010.06614.x
Valinksy, J. 2018. McDonald’s removing artificial additives from its burgers. CNN Money. https://money.cnn.com/2018/09/27/news/companies/mcdonalds-artificial-ingredients/index.html
Walker AW, Duncan SH, McWilliam LEC, Child MW, and Flint HJ. 2005. pH and peptide supply can radically alter bacterial populations and short-chain fatty acid ratios within microbial communities from the human colon. Applied Environmental Microbiology. 71(7):3692-3700. https://www.ncbi.nlm.nih.gov/pubmed/16000778/