L-Glutamine

With glutamine, the science of how it works is far more impressive than the trials in healthy people. These are the questions our naturopaths ask in store to help you tell the two apart.

A good fit if

• Your gut lining is the reason, and you'll take a powder at a dose you can actually reach
• You can give it eight weeks, which is how long the one strong gut trial ran
• You'd rather buy the plain powder than a peptide blend with an unproven absorption story
• Your kidneys are healthy and you take no prescription medicines
• You're comfortable with an honest maybe. The theory is good, but the combined trials across mixed groups of people found no effect

Check with us first if

• You have any kidney concern. In people with diabetic kidney disease, glutamine can cause kidney scarring (glomerulosclerosis) and raised creatinine. It's the clearest safety signal outside hospital.
• You have liver disease or anything that affects how your body handles ammonia. Your body breaks glutamine down into glutamate and ammonia, which both affect your nervous system.
• You plan to take it long term. The safety research says plainly that long-term use by healthy people of all ages hasn't been fully studied.
• You have type 2 diabetes. 30 g a day for six weeks made no difference to blood sugar or insulin after meals, so it isn't a blood sugar strategy either way.
• You take any prescription medicine. No specific interaction with glutamine taken by mouth has been recorded, but no data doesn't mean no interaction.
• You're buying it for training. A review of 47 studies found no benefit, and a protein powder is the better choice for recovery.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before you start.

• L-glutamine free-form powder. Best known for: The standard product on the shelf: a plain crystalline amino acid that's almost tasteless and dissolves in water. Absorption: We hold no direct absorption comparison; every gut trial used glutamine taken by mouth. Typical use: The form used in the one strong gut trial at 5 g three times a day, and the only format you can realistically use to reach 15 g a day.
• L-glutamine capsules and tablets. Best known for: The same substance in a smaller dose per capsule or tablet. Absorption: No separate evidence. It's the same molecule. Typical use: Convenience only. Getting to 15 g a day means 15 to 30 capsules depending on strength, which is the practical problem with this format.
• Alanyl-glutamine dipeptide. Best known for: Two amino acids joined together, more stable in liquid, which is why hospital drip products use it. Absorption: We hold no comparison of how it's absorbed by mouth against free glutamine. Typical use: Allowed in Australia only in medicines taken by mouth. Every trial we hold gave it by drip or in dialysis fluid, and those results don't carry over to a scoop of powder.
• Effervescent glutamine. Best known for: A tablet that dissolves in water. Absorption: Not compared in studies. Typical use: One small trial gave 12.4 g a day for 60 days to 30 older adults and found no change in anything measured and no side effects.
• Glutamine in arginine or HMB combination formulas. Best known for: Sold as recovery or wound-repair blends. Absorption: Not applicable. Typical use: The results are mixed up with the other ingredients. A 15-study review says glutamine was only tested together with arginine, which limits what we can learn about it on its own. Never credit a blend's result to the glutamine in it.
• Glutamine peptides (protein hydrolysate powders). Best known for: Sold as better absorbed than free glutamine. Absorption: None of the evidence we hold supports that. Typical use: A hydrolysate is a different ingredient from the permitted glutamine entry, and the better-absorbed claim has no source behind it.
• Glutamic acid and glutamate. Best known for: Different substances that get mixed up with glutamine because the names are similar. Absorption: Not applicable. Typical use: In Australia, glutamic acid is allowed only in medicines applied to the skin. It isn't a substitute for glutamine taken by mouth, and monosodium glutamate is a different substance again.

Reference values. There isn't one. Glutamine has no Australian reference value. It isn't one of the nutrients the NHMRC covers, so there's no recommended intake and no percentage of daily needs. Any figure given that way has been made up.

Typical supplemental range. Australian powders are usually taken at about 5 g a scoop, one to three times a day. In the trial for gut trouble after an infection, people took 15 g a day as 5 g three times a day for eight weeks. That's the one dose that both matches what's sold here and has a strong result behind it. Other trials used 12.4 g a day for 60 days in older adults, and 30 g a day for six weeks in type 2 diabetes, which had no effect on blood sugar or insulin. In athletes, short-term doses of 20 to 30 g within a few hours, and 0.1 g per kilo four times a day for two weeks, caused no significant side effects.

Upper level. There's no legal limit, so every limit here is based on the evidence rather than the rules. The general view is that up to 30 g a day can be taken without important side effects. Above 200 mg per kilo of body weight, an analysis of athlete studies found a drop in neutrophils, a type of white blood cell. That isn't a benefit, and it's worth knowing if you dose by the scoop rather than by your weight.

Worth knowing. There's less to say about timing than the marketing suggests. The only routines we've seen tested are three doses spread across the day, and one trial that gave it in half a glass of ice-cold water 5 to 10 minutes before each main meal. Nothing supports taking it on an empty stomach or in a post-workout window, so don't let a label tell you otherwise. What you need depends on your age, diet and health, so talk to one of our naturopaths.

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• Critically ill adults with multiple organ failure. Early glutamine given by drip and feeding tube together was linked with more deaths at 28 days, in hospital and at 6 months.
• Diabetic kidney disease or reduced kidney function. Glutamine can cause kidney damage (glomerulosclerosis) and raised blood creatinine in that setting.
• Liver disease, or any condition that affects how your body handles ammonia. Glutamine is broken down into glutamate and ammonia, which both affect the nervous system.
• Planning to take it long term. The safety research says long-term use by healthy people of all ages hasn't been fully studied.
• Pregnancy and breastfeeding. There's no evidence either way, so see a practitioner rather than assuming it's fine.
• Children. It was tolerated in supervised clinical trials, but no over-the-counter dose for healthy children has been set.
• More than 200 mg per kilo of body weight. A meta-analysis in athletes found lower neutrophils (a type of white blood cell) at that level.
• If you take prescription medicine. No interaction is documented, which isn't the same as no interaction existing.
• We couldn't check TGA safety advisories for glutamine, so we cannot say whether any exist.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before you start.