You scroll past a jar of powder with a glossy label. For your gut. For your recovery. For your immune system. One voice says: take this supplement. The next says: no, just eat meat. And yet another swears by raw pointed cabbage. You stand there with your phone in your hand and think: who is actually right?

I once walked around with the same question. During my training I gave a presentation on glutamine. What I came across then moved me: a small molecule that plays an enormous role in our intestines, especially in seriously ill people. Precious information, I thought. And years later I saw that same molecule again — no longer in a hospital bed, but in hundreds of jars online, with promises that kept growing.

So today I want to explain calmly what we really know. Not what sells. What is true.

What is glutamine, actually?

Glutamine is an amino acid: one of the building blocks your body uses to make proteins. What is special is that it is the most abundant free amino acid in your blood and your muscles. Your body considers it so important that it keeps a large store of it.

For a long time glutamine was called “non-essential”. That sounds unimportant, but it means something else: your body can make it itself, so you do not strictly have to get it from food. Since around 1990, researchers prefer to call it conditionally essential. And that word is the key to this whole story.

Picture your muscles as a bakery baking glutamine all day, an estimated 40 to 80 grams a day (the exact amount varies by source; in fairness, this is an estimate). Your food adds a few grams on top. For a healthy body that is more than enough. The bakery runs, the shelves are full.

But in a seriously ill patient — think severe burns, major surgery, blood poisoning — something happens. The body suddenly uses much more glutamine than normal, while the bakery is faltering. Demand exceeds supply. At that moment glutamine becomes essential. Hence the word “conditional”: it depends on the circumstances.

Why do your intestines love it so much?

Here it becomes lovely. Your intestinal wall is actually only one cell layer thick, a thin border between the outside world in your gut and the rest of your body. Imagine a wall of sentries standing side by side, holding on to each other firmly. Together they decide what may come in (nutrients) and what must stay out (bacteria, toxins).

Those sentries work extremely hard. They are constantly worn down and replaced. And their favourite fuel? Glutamine. The cells of your small intestine use so much glutamine that the small intestine alone is responsible for about a third of the total glutamine use in your body.

Glutamine does three things at once for that intestinal wall. It is fuel, so the cells have energy to divide and renew. It helps keep the “handholds” between the sentries (the so-called tight junctions) firm, so the wall stays closed. And it is a raw material for glutathione, one of the most important antioxidants in your body, a kind of cleaning crew that clears up damage.

In animal studies you see what happens when that fuel falls away: the intestinal wall shrinks, becomes leaky, and bacteria slip through more easily. That explains why glutamine seemed such a promising idea in sick people.

Can we get enough from food?

For most healthy people: yes, amply. And that is precisely what the jars would rather not tell you.

Consider: your own bakery already makes tens of grams a day. Food comes on top of that. An average diet provides roughly 3 to 10 grams of glutamine a day, depending on how much protein you eat. If you eat a lot of animal protein — meat, fish, eggs, dairy — you are at the upper end. If you eat plant-based, often a little lower, because total protein intake is then usually lower. But beans, spinach, parsley and indeed cabbage also contain glutamine.

Two honest nuances. First: cooking breaks down some of the glutamine; heat converts it into other substances. That is why people sometimes mention raw cabbage or spinach. But do not worry — the amount you “lose” this way is negligible, for a healthy body, next to what you make yourself. Second, and more importantly: the fact that a molecule is important does not mean you need more of it. Oxygen is vital. Yet you do not breathe better by buying extra oxygen if your lungs are healthy.

Which supplement form is “better”?

Good question — and the answer differs by situation.

Free L-glutamine is the form you find in most powder jars. For taking by mouth that is fine. But for delivery through a drip, free glutamine is awkward: it dissolves poorly and slowly falls apart in liquid (releasing ammonia, among other things). You cannot store it stably in a drip bag.

That is why hospitals use a cleverer form: a dipeptide, usually alanyl-glutamine. By firmly linking the glutamine to another amino acid (alanine), it becomes more than ten times more soluble and stable enough to sterilise. Once in the blood, the link is snipped apart at lightning speed and the glutamine is released after all. For clinical, intravenous use the dipeptide is therefore clearly better.

But notice the shift happening here: this is about patients in a hospital bed. For a healthy person at home, the honest “best form” is not a powder or a dipeptide. It is a plate with enough protein on it.

Who really benefits — and what went wrong?

Here comes the part I did not yet consider during my presentation, and which science only showed clearly later.

The first, small studies were hopeful. In patients fed entirely through a drip, extra glutamine sometimes seemed to help: fewer infections, better blood-sugar regulation. In 2009 the European guideline (ESPEN) even strongly recommended glutamine for drip feeding in intensive care.

And then came the big test. In 2013, a study of 1223 seriously ill patients with multiple organ failure appeared in the New England Journal of Medicine (the REDOXS study). Researchers gave them a high dose of glutamine, early and in large amounts, as if it were a medicine. The expectation was: this will save lives.

The opposite happened. The group that received glutamine did not do better and even had a higher mortality. Most of the harm was precisely in the very sickest patients, with kidney and organ failure.

That is an uncomfortable outcome, and that is exactly why it matters. It shows that a body is not a stove where more fuel automatically gives more power. In a body already overloaded, “more” can become a burden instead of a help.

Since then the guidelines have become cautious. The current ESPEN guideline (2023) puts it like this: in unstable, complex intensive-care patients, certainly with liver or kidney failure, you should give no glutamine through the drip. For most intensive-care patients, extra glutamine through feeding is also discouraged. For a long time severe burns were a possible exception. But even there, a large study from 2022 (RE-ENERGIZE, more than 1200 patients) showed no clear benefit, which means that recommendation is being looked at again too.

In other words: the group that may benefit is small and specific — certain patients fed entirely through a drip without organ failure, and possibly some situations with a damaged or too-short bowel. Not the healthy person who wants to live more productively. And certainly not the very sickest.

What I take from this

Glutamine is not a miracle cure, and not nonsense either. It is something far more interesting: a molecule that is genuinely important for your intestines, and which your body normally takes care of perfectly well on its own. The story of glutamine is really the story of almost every supplement: important in the body is not the same as useful in a jar.

And that science dared to revise its own expectation, from “this saves lives” to “this can, in certain cases, harm,” is not a weakness. It is the loveliest thing honest research can do.

Do you have a health question about your gut, your nutrition or a supplement you are considering? Please discuss it with your GP or a specialist. This blog is here to help you understand, not to give medical advice.

I leave you with one gentle question, to carry with you. Which “more” in your life have you added because it sounded healthy, without asking whether your body already had enough?

Related reading

• Liquid Gold, or Liquid Marketing? What Science Really Knows About Olive Oil
• What Really Happens During a Hangover
• What’s Really in Your Teabag? On Plastic, Bleach and Hot Water

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Sources

• Heyland DK, et al. A randomized trial of glutamine and antioxidants in critically ill patients (REDOXS). New England Journal of Medicine. 2013;368(16):1489–1497. DOI: 10.1056/NEJMoa1212722. Accessed via PubMed.
• Heyland DK, et al. A Randomized Trial of Enteral Glutamine for Treatment of Burn Injuries (RE-ENERGIZE). New England Journal of Medicine. 2022;387(11):1001–1010. DOI: 10.1056/NEJMoa2203364. Accessed via PubMed.
• Wang B, et al. Glutamine and intestinal barrier function. Amino Acids. 2015;47(10):2143–2154. DOI: 10.1007/s00726-014-1773-4. Accessed via PubMed.
• Singer P, et al. ESPEN practical and partially revised guideline: Clinical nutrition in the intensive care unit. Clinical Nutrition. 2023. (Caution on glutamine in unstable ICU patients and in liver/kidney failure.)
• Singer P, et al. ESPEN Guidelines on Parenteral Nutrition: Intensive care. Clinical Nutrition. 2009;28(4):387–400. (Earlier strong recommendation for glutamine in parenteral nutrition.)

The estimated figures for the body’s own production (≈40–80 g/day) and dietary intake (≈3–10 g/day) are estimates that vary by source and by diet.