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Evidence Based

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L-Glutamine Benefits and Uses: Why This Amino Acid Matters

Written by Dr. Michael Ruscio, DC on September 3, 2025

Written by Dr. Michael Ruscio, DC on September 3, 2025 — Reviewed by Hannah Wright

• What Is Glutamine?|
• Gut Benefits|
• Immune Benefits|
• Brain Benefits|
• Muscle Benefits|
• How to Get L-Glutamine|

Gas, bloating, food sensitivities, low energy, and brain fog—if these sound familiar, your body may be burning through more glutamine than it can replace. This amino acid does far more than help build protein. It fuels the cells lining your gut, powers your immune defenses, and even helps regulate brain chemistry.

When stress, illness, or overtraining push your glutamine demand higher than your supply, the result can be a cascade of symptoms that don’t respond to diet or lifestyle changes alone. That’s why understanding the benefits of glutamine—and how to replenish it—is so important.

What Is Glutamine?

Glutamine is the most abundant amino acid in the human body, and most of it is made in skeletal muscle 1. The type of glutamine that’s biologically active in humans is L-glutamine—I’ll refer to the general amino acid as glutamine and the supplement as L-glutamine in this article. 

Although glutamine is technically classified as a “non-essential” amino acid—meaning your body can normally make enough on its own—that label can be misleading. 

Under periods of stress, illness, infection, injury, or intense exercise, your body’s demand for glutamine can exceed its ability to produce it. In these cases, glutamine becomes what’s called “conditionally essential,” meaning you need to get more through food or supplementation to keep up 2.

What makes glutamine unique compared to other amino acids is that it’s not just a building block of protein. It acts as a fuel source for multiple systems in the body, including the:

• Gut lining 2
• Immune system 2
• Brain 3
• Muscles 1

This multi-system role is why glutamine deficiency—often triggered by stress or chronic illness—can have ripple effects throughout the body, possibly playing a role in gut issues, brain fog, immune dysregulation, and slow recovery.

Glutamine Nourishes and Protects the Gut Lining

Your intestinal lining is only one cell thick, yet it covers a surface area the size of about half a badminton court (32 square meters) 4. These cells (called enterocytes) do more than absorb nutrients. They regulate what gets into your bloodstream, defend against invaders, and help control how your immune system responds to food.

Unlike most cells, enterocytes rely almost entirely on glutamine—not glucose—as their primary energy source 2. Without glutamine, they can’t renew themselves, maintain tight junctions (seals between cells that keep the gut from leaking), or preserve the gut barrier.

What Happens Under Stress

During times of stress, like when you’re sick, overtraining, or dealing with an injury, your immune system and other parts of the body compete for glutamine 2. As more glutamine is redirected to fuel the body’s immune responses, the gut lining can become depleted, leading to:

• Slower cell renewal
• Loosening of tight junctions in the gut
• Too much intestinal permeability (“leaky gut”)

This breakdown may contribute to food sensitivities, chronic inflammation, and body-wide reactivity. What’s worse, people often cut out glutamine-rich foods (like meat, eggs, and legumes) when they’re stressed, creating a vicious cycle of low intake and worsening gut function.

Glutamine Fuels a Balanced and Resilient Immune System

Your immune system is one of the hungriest systems in your body. When it kicks into gear—whether from fighting an infection, recovering from intense exercise, or healing from surgery—it needs a steady supply of fuel to keep white blood cells working to protect your body from damage.

That’s where glutamine comes in. Immune cells use glutamine not just for energy, but also as raw material to 2:

• Multiply quickly when your body needs more defenders
• Copy DNA so the body can make new immune cells 
• Make antioxidants like glutathione, which protects immune cells from the stress of inflammation

When glutamine levels drop, your immune system can’t keep up. White blood cells slow down, inflammation becomes harder to regulate—possibly becoming chronic—and your body has a harder time fighting off infections 2.

What Research Shows

• Hospital settings: Studies show L-glutamine supplements can lower infection rates, speed up recovery, and support post-surgical immune function in critically ill or surgical patients 5.
• Athletes: Combat athletes supplementing with L-glutamine had stronger immune defenses (measured by salivary IgA, a key first-line antibody) and fewer colds or sinus infections during training. They also showed more balanced hormones related to stress, suggesting better resilience under heavy training loads 6.
• Post-viral illness: In COVID-19 patients, L-glutamine supplements may have helped reduce inflammatory cytokines and improve appetite 7.

Why It Matters

Glutamine doesn’t just “boost” your immune system—it helps keep it stable and well-fueled. Without enough, the immune system can swing between being sluggish (letting infections drag on) and being overactive (triggering unnecessary inflammation or food sensitivities).

In short, glutamine acts like the steady fuel line that keeps your immune defenses running smoothly, especially when your body is under stress.

Glutamine Supports Mental Clarity and Calm

Glutamine is the main raw material for perhaps the brain’s two most important neurotransmitters:

• Glutamate (known especially for its role in focus, learning, memory, and wakefulness)
• GABA (with a major role in calmness, relaxation, and sleep)

The glutamate–glutamine cycle—how brain cells recycle glutamate into glutamine and back—ensures neurons have a steady supply of these neurotransmitters while protecting against overstimulation 3.

But under chronic stress or inflammation, glutamine may be shunted away from the brain toward the gut and immune system—leaving neurotransmitter production compromised 2. This may lead to:

• Brain fog
• Anxiety and irritability
• Mental fatigue
• Poor memory and focus
• Trouble sleeping

One study showed that people with relatively more glutamine than glutamate in the brain’s motivation center had better stamina, less fatigue, and lower perceived effort during demanding tasks 8.

That means glutamine may not just support neurotransmitter balance—it may also enhance mental resilience and endurance. So, it’s important to keep glutamine levels up.

Glutamine Helps Preserve Muscle During Stress and Recovery

Because glutamine is stored in large amounts in your muscles, L-glutamine is often marketed as a muscle-building supplement. But the truth is a little different.

Glutamine doesn’t directly make your muscles grow the way nutrients like protein or the amino acid leucine do 9. Instead, it seems to work more like a backup fuel source and a helper during recovery.

When your body is under stress—from illness, injury, surgery, or even intense workouts—it starts pulling glutamine from your muscle stores to keep your gut, immune system, and brain running 2. This is why people often notice faster muscle loss when they’re sick, overtrained, or recovering from trauma. Your muscles are essentially donating their glutamine to more critical systems.

Where glutamine seems to shine is in muscle preservation. It may help by 2:

• Reducing muscle breakdown when your body is under heavy stress
• Supporting recovery after exhausting workouts or injury
• Helping preserve lean mass in situations like infections, burns, or long periods of inactivity

So, rather than being a muscle builder, glutamine may be more of a muscle protector. Think of it less like creatine (which can boost performance and growth) and more like an insurance policy that may help you hold onto muscle and recover better when your body is under strain.

How to Get L-Glutamine Safely and Effectively

If you’re considering taking supplemental L-glutamine, here’s how to use it safely and effectively:

1. Dose

• General support: 5–10 grams per day
• In more depleted situations (leaky gut, stress, illness, etc.): 10–30 g/day, divided 2–3 times daily

2. Timing

• For gut health: Take it on an empty stomach 30–60 minutes before meals.
• For recovery: Take it after a workout with electrolytes or carbs.

3. Duration

• For most people, 2–3 months is long enough to meet demand.
• In more complex or chronic cases, longer use can be considered—but should be guided by symptom response and clinical context.

4. Form

• Pure L-glutamine powder, unflavored, no additives
• Capsules are okay for low doses but can be impractical for higher doses.

5. Food Sources

• Meat, fish, eggs, legumes, and bone broth are naturally rich in glutamine
• The average diet supplies 3–6 g/day
• People with sensitive guts on highly restricted diets or those who eat a vegan diet may need to lean on L-glutamine supplementation more to achieve meaningful benefits.

The Takeaway: Why L-Glutamine Benefits Extend Across Systems

Glutamine isn’t just another amino acid—it’s a multi-system fuel that helps keep your gut, immune system, brain, and muscles functioning under stress. When your body runs low on glutamine, repair may slow down, inflammation may rise, and recovery may get harder.

Supplementing strategically—or simply restoring L-glutamine through food—can help break the cycle and rebuild resilience.

If you’ve been struggling with gut issues, fatigue, brain fog, or slow recovery, L-glutamine may be one piece of the puzzle. But it’s almost certainly not the only one. At the Ruscio Institute for Functional Medicine, we specialize in identifying where your system is breaking down and creating personalized protocols that restore health step by step.

If you’d like help figuring out whether L-glutamine or other gut and immune supports are right for you, reach out to our clinic here. Our team would be happy to guide you.

The Ruscio Institute has developed a range of high-quality formulations to help our clients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you. The information on DrRuscio.com is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.