Published May 23 2016
Some researchers theorize that everyone with an autoimmune condition such as Graves’ Disease and Hashimoto’s Thyroiditis has an increase in intestinal permeability, also known as a leaky gut. I’m not sure if this is the case, but I can say that many of the patients I have seen over the years have tested positive for a leaky gut. One of the most common nutrients used to help heal a leaky gut by natural healthcare professionals is L-glutamine. In fact, I personally recommend L-glutamine to many of my patients. However, I’ve had some patients express concerns that L-glutamine can actually cause harm, and so I figured I’d put an article together to discuss this.
Glutamine is an amino acid, and in the blood it is considered to be the most abundant free amino acid (1) . Research shows that glutamine is an important nutrient for rapidly dividing cells, including cells from the immune system and the gut (2) . With regards to helping to heal a leaky gut, glutamine is the primary energy source for enterocytes, which are the cells of the small intestine (3) . And numerous studies show that taking glutamine can help to reduce intestinal permeability (4)  (5)  (6) . This is the primary reason why many doctors recommend L-glutamine to those patients who have a suspected or confirmed leaky gut.
Other Functions Of L-Glutamine
Let’s go ahead and look at some of the other important functions of L-glutamine:
Synthesis of neurotransmitters. Glutamine is an essential precursor for the biosynthesis of amino acid neurotransmitters (9) .
Improves Insulin Response. A small randomized study on type 2 diabetics showed that oral L-glutamine (as well as whey protein) restored insulin response (10) . In fact, there is some evidence that it might do this too well, and thus taking large doses of L-glutamine might cause problems in some people with hypoglycemia (11) .
Acid-base balance in the kidney. Glutamine plays an important role in acid-base balance, and it is the primary amino acid involved in renal ammonia-genesis, which is a process that relates to acid excretion (12)  (13) .
Is Glutamine An Excitotoxin?
Glutamine itself isn’t an excitotoxin. However, it can convert into glutamate, which in turn can cause excitotoxicity in some people. Specifically, if someone has a defective glutamine-glutamate-GABA cycle then this can lead to the buildup of glutamate. However, if this is working properly then glutamine does get converted into glutamate, but this in turn gets converted into GABA. So yes, in a small percentage of people taking L-glutamine this can lead to excessive amounts of glutamate. However, most people will know this upon taking a small amount of L-glutamine, and so if this is a concern you of course can start with very small doses of L-glutamine, and if all goes well can then gradually increase it.
Can Taking L-glutamine Cause Cancer?
There is evidence that taking L-glutamine can increase the growth of certain tumors (16)  (17) . In other words, if someone has a malignancy then it might be best to play it safe and avoid L-glutamine. However, there is no evidence I’m aware of which shows that taking large doses of L-glutamine can increase the risk of developing cancer.
This still brings up some controversy, as some will argue that a person might have cancer and not know about it, and if this is the case and they supplement with L-glutamine then this might cause the tumor to grow. On the other hand, having a healthy gut is important for a healthy immune system, which in turn is necessary to keep cancer in check. So there is also the argument that not doing everything you can do to heal the gut isn’t a wise approach. Also keep in mind that not all cancer cells are glutamine dependent, although many are. This is definitely a controversial topic, and after reading this some people might feel more comfortable consuming food sources of L-glutamine, such as bone broth.
Should Those With Neurodegenerative Diseases Avoid L-glutamine?
If someone has a neurodegenerative condition then it probably is best to play it safe and not supplement with L-glutamine. And the reason for this is because problems with glutamate may be behind the pathogenic mechanisms of certain neurodegenerative conditions such as Huntington’s disease, Alzheimer’s disease, Parkinson’s disease, an amyotrophic lateral sclerosis (18)  (19) .
What Are Some Good Food Sources Of Glutamine?
Bone broth is probably the best source of glutamine, which is why many healthcare professionals recommend bone broth for healing the gut. A good vegetarian source of glutamine is cabbage. Other sources of glutamine include grass-fed beef, chicken, fish, and eggs.
You might wonder if you can rely on food sources of glutamine to heal the gut. The answer is “yes”, as while I do commonly recommend L-glutamine supplements to my patients in a form of a powder, it is possible to heal the gut by drinking bone broth on a daily basis, which I also commonly recommend. In fact, the GAPS diet heavily relies on bone broth for healing the gut. However, if someone doesn’t want to drink bone broth then they can just supplement with L-glutamine. But it is possible to heal the gut just by drinking a lot of bone broth and not by taking L-glutamine.
In summary, glutamine is the most abundant free amino acid in the blood, and it is the main energy source for the cells of the small intestine. Numerous studies show that taking glutamine can help to heal a leaky gut, which is why many doctors recommend L-glutamine to their patients. Glutamine has other functions as well, as it can reduce inflammation, it’s involved in the synthesis of neurotransmitters, it can improve insulin response, it plays a role in acid-base balance, and it is a precursor for glutathione. There is some controversy over whether glutamine can cause excitotoxicity, and some are concerned about the role it plays in the growth of tumors. Bone broth and cabbage are two excellent food sources of L-glutamine, while other sources include grass-fed beef, chicken, fish, and eggs.