Glutamate
Glutamate is an amino acid as well as the most abundant neurotransmitter in the human body. Glutamate has an excitatory effect on neurons, which can potentially make certain symptoms, like ADHD and anxiety, worse.
Quick Facts
What is glutamate?
Glutamate, also known as glutamic acid, is an amino acid. Amino acids are the building blocks of proteins. Glutamate is found in both plant and animal proteins.
Glutamate also functions as a neurotransmitter and it is the most abundant neurotransmitter in the human body. Neurotransmitters are chemicals that nerve cells use to transmit messages. Glutamate has an excitatory effect on neurons, meaning it makes the neuron more likely to fire. [8]
Under normal conditions, glutamate is transformed and recycled to glutamine, in the brain by glial cells. Glutamine is not excitatory.
Glutamate is essential for memory, learning, behavior, motor activity and more. [3]
Other conditions are also associated with excess glutamate, like OCD, seizures, ADHD and anxiety. These symptoms are also common among those with autism
Although it hasn’t been studied extensively, some people hypothesize that L-glutamine supplementation could increase excitability (hyperactivity, anxiety, etc) in those with autism/ADHD due to its conversion to an excitatory neurotransmitter called glutamate that is already seen increased in those with these disorders (see the L-Glutamine note for more information).
Common sources of glutamate
Glutamate is obtained through diet and our bodies can also make it.
Glutamate was discovered in 1908 and was found to give foods a savory taste. [10]
Many foods contain glutamate naturally but it is in a bound form, meaning it is connected to other amino acids.
Processed Foods
Glutamate can also be found in many processed foods in the form of “free glutamate” and the most common form of free glutamate is monosodium glutamate (MSG). This is the most common form because sodium is so abundant in processed foods and connects with the glutamic acid molecule. The two terms, monosodium glutamate and “free glutamate”, are often used interchangeably.
Fermented or Manufactured Foods
Free glutamate is created through fermentation or through food manufacturing processes. Free glutamate refers to glutamate that is not bound to other amino acids. Free glutamate can be found in some natural foods that have undergone fermentation. Free glutamate is also added to processed foods to enhance the flavor.
There is concern that the manufacturing processes used to create free glutamate also create harmful impurities/byproducts like heterocyclic amines. [11]
Glutamate from natural foods enters the body in a slow, controlled way through the normal process of digestion. Foods with high amounts of free glutamate (i.e. Monosodium Glutamate, or, MSG) cause a large influx into our bodies and this is problematic for some people, leading to a range of symptoms.
Foods containing Glutamate
Foods containing added MSG must list it in the ingredient panel as monosodium glutamate.
If MSG occurs naturally in foods it does not need to be included on the label.
While nearly all foods contain some levels of glutamate, the foods listed below are especially high in free glutamate:
Aged cheeses (parmesan, roquefort) or cured meats
Fermented foods
Fish sauce
Yeast and yeast extracts
Soy sauce
Soy protein
Bouillon or stock
Bone broths and braised meats
Grape juice
Gluten and casein (from wheat and dairy products)
Malted barley
Texture proteins or protein isolates
Cooking proteins on high temperatures (about 300 degrees Fahrenheit) and adding vinegar to proteins while cooking causes the release of free glutamate.
For a comprehensive list of all alternative names of glutamate, click here.
For a list of glutamate-containing foods (and glutamate-free foods) click here.
MSG alternatives
In all of the following alternatives, always check the ingredient list to ensure there is no added MSG:
Beef stock
Coconut aminos
Soy sauce (avoid if gluten-free)
Chemical reactions
The body can respond to foods and/or chemicals in many different ways including allergies and sensitivities. If you suspect a chemical reaction, you can either choose to avoid the chemical or additional testing. Read more about food reactions.
Glutamate & Autism in the Research
Excessive Glutamate levels in asd
Studies have shown that people with autism often have high plasma and serum glutamate levels. Excess glutamate can be problematic because it causes overexcitation and can have neurotoxic effects. [1, 3, 5, 6, 7]
The reasons behind the excess glutamate are unclear. It may be due to the diet but it may also be due to issues with glutamate receptors or a reduced ability to clear glutamate and recycle it back to glutamine. [7] Is an overabundance of glutamate a result of autism or is it the cause? Research is ongoing to answer these questions. It is also unclear whether free glutamate is problematic for everyone or just individuals who have a sensitivity.
There has been debate whether blood tests are an accurate representation of glutamate levels in the brain but it seems that studies have shown that the two are correlated. [3]
health issues associated with high glutamate
Other conditions are also associated with excess glutamate, like seizures, ADHD and anxiety. These symptoms are also common among those with autism. [1]
There is a theory that brain injuries impact the glial cells ability to recycle glutamate to glutamine. [3]
There is also debate among researchers whether or not glutamate from the diet can cross the blood brain barrier and impact the brain. Some researchers posit that the integrity of the blood brain barrier can be compromised by low grade inflammation in the body, allowing excess glutamate to reach the brain. [9]
References
[1] Rojas DC. The role of glutamate and its receptors in autism and the use of glutamate receptor antagonists in treatment. J Neural Transm (Vienna). 2014;121(8):891-905.
[2] Naaijen J, Zwiers MP, Amiri H, et al. Fronto-Striatal Glutamate in Autism Spectrum Disorder and Obsessive Compulsive Disorder. Neuropsychopharmacology. 2017;42(12):2456-65.
[3] Zheng Z, Zhu T, Qu Y, Mu D. Blood Glutamate Levels in Autism Spectrum Disorder: A Systematic Review and Meta-Analysis. PLoS One. 2016;11(7):e0158688.
[4] Fernell E. Further studies of GABA and Glutamate imbalances in autism are important challenges for future research. Acta Paediatr. 2019;108(2):200-1.
[5] Khalifa D, Shahin O, Salem D, Raafat O. Serum glutamate was elevated in children aged 3-10 years with autism spectrum disorders when they were compared with controls. Acta Paediatr. 2019;108(2):295-9.
[6] Cai J, Ding L, Zhang JS, Xue J, Wang LZ. Elevated plasma levels of glutamate in children with autism spectrum disorders. Neuroreport. 2016;27(4):272-6.
[7] Ghanizadeh A. Increased glutamate and homocysteine and decreased glutamine levels in autism: a review and strategies for future studies of amino acids in autism. Dis Markers. 2013;35(5):281-6.
[8] El-Ansary A, Al-Ayadhi L. GABAergic/glutamatergic imbalance relative to excessive neuroinflammation in autism spectrum disorders. J Neuroinflammation. 2014;11:189.
[9] Obrenovich MEM. Leaky Gut, Leaky Brain. Microorganisms. 2018;6(4):E107.
[9] U.S. Food and Drug Administration. 2012. Questions And Answers On Monosodium Glutamate (MSG). [online] Available at: <https://www.fda.gov/food/food-additives-petitions/questions-and-answers-monosodium-glutamate-msg.> [Accessed 25 October 2020].
[10] Truthinlabeling.org. n.d. Manufactured Vs Natural Glutamic Acid. [online] Available at: <https://www.truthinlabeling.org/manufacvsnatural.html> [Accessed 25 October 2020].
