Glutamine Instead of Glucosamine? What the Research Shows

Table of Contents

1. The Idea, Stated Fairly
2. The Chemistry Behind It: Glucose + Glutamine → Glucosamine
3. Part One: Does Glutamine Lower Blood Sugar in People?
4. Where the Glutamine Results Fell Short
5. Part Two: How Glutamine Actually Works — a Gut Signal
6. Why the Glucosamine Pathway Cannot Be a Glucose Drain
7. The Twist: More Hexosamine Flow Is the Insulin-Resistance Signal
8. Glutamine vs Glucosamine, Side by Side
9. Cautions Before Anyone Tries Glutamine
10. Food First: Where Glutamine Comes From
11. The Verdict
12. Key Research Papers
13. Connections
14. Featured Videos

The Idea, Stated Fairly

The research on glucosamine supplements finds little or no joint benefit, and it raises a particular concern for people with diabetes, prediabetes, high fasting glucose or an elevated HbA1c (the findings are laid out on Glucosamine, Blood Sugar and Diabetes). That leaves a natural follow-up question, and it is a clever one.

Every cell makes glucosamine for itself. The recipe, covered step by step on How the Body Makes Glucosamine, starts with a molecule derived from glucose and adds an amino group taken from the amino acid glutamine. So the reasoning goes:

1. Glucosamine is made from glucose plus glutamine.
2. If you supply extra glutamine, the body can make more of its own glucosamine.
3. Making that glucosamine uses up glucose — so the excess sugar in the blood gets spent on something useful instead of lingering.
4. Therefore glutamine is the smarter supplement: it gives you glucosamine the natural way and lowers blood sugar at the same time.

Each step sounds reasonable. The way to judge the idea is to test each step against what has actually been measured, which is what the rest of this page does. Two questions do most of the work: does glutamine lower blood sugar in humans, and if it does, is that because glucose is being turned into glucosamine?

Back to Table of Contents

The Chemistry Behind It: Glucose + Glutamine → Glucosamine

Glucose entering a cell is first converted into fructose-6-phosphate, a normal stop on the way to being burned for energy (glycolysis). At that point a small side road branches off: the hexosamine pathway. Its first and rate-limiting enzyme, glutamine:fructose-6-phosphate amidotransferase — usually shortened to GFAT — takes the amino group from glutamine and attaches it to fructose-6-phosphate, producing glucosamine-6-phosphate. A few further steps turn that into the pathway's main end product, UDP-N-acetylglucosamine (UDP-GlcNAc), the building block the body uses to put sugar chains on proteins and fats, including the large molecules of cartilage.

Milewski's review of the enzyme describes GFAT as catalysing "the first committed step" of this pathway and as "an important point of metabolic control" — in other words, it is the gatekeeper that decides how much glucose goes down the side road. Buse's 2006 review calls the hexosamine pathway "a relatively minor branch of glycolysis."

So the owner's premise is correct on the chemistry: glucose and glutamine really are the two raw materials. The question is what controls the flow, and how big that flow can get.

Back to Table of Contents

Part One: Does Glutamine Lower Blood Sugar in People?

Here the idea gets real support. A small group of researchers in Cambridge, Sydney, Adelaide and Tehran has tested oral glutamine in people, mostly in type 2 diabetes. The doses are large — 15 to 30 grams, far more than a capsule — but the findings are human findings, which is more than glucosamine can claim for blood sugar.

Alongside the trials there is one large observational study. Cheng and colleagues measured 45 blood metabolites in 1,015 people from the Framingham Heart Study and 746 from a Swedish cohort. Higher blood glutamine went with less insulin resistance in both groups, and a high glutamine-to-glutamate ratio went with a lower risk of developing diabetes in Framingham (odds ratio 0.79) — though that diabetes finding did not repeat in the Swedish group. In mice, giving glutamine improved glucose tolerance. An association in blood levels is not proof that a supplement helps, but it points the same way as the trials.

So step one of the idea, "glutamine can lower blood sugar," has genuine human evidence behind it.

Back to Table of Contents

Where the Glutamine Results Fell Short

Honest reporting means giving the weak spots the same space as the strong ones:

• The largest after-meal trial was negative. Mansour 2020, with 33 people per group over 6 weeks, found no significant difference in after-meal glucose or insulin between glutamine and placebo.
• The 4-week HbA1c result had no glutamine-free arm. In Samocha-Bonet 2014, both arms took glutamine (one with sitagliptin, one with placebo), so the fall in HbA1c cannot be separated from time, attention or seasonal change. The authors themselves reported "no significant time-treatment interactions."
• Glutamine given straight into the intestine did not lower glucose. When Chang and colleagues infused glutamine directly into the duodenum, bypassing the stomach, it still raised GLP-1, GIP and insulin — but blood glucose did not fall, probably because glucagon rose too.
• Glutamine was no better than food protein. In Samocha-Bonet 2015, 25 g of ordinary whole protein restored the first-phase insulin response as well as 25 g of glutamine did.
• The trials are small and short. The biggest enrolled 66 people; none ran longer than 6 weeks; none measured diabetes complications, which are what actually matter to patients.

The fair summary: glutamine with a meal can blunt the post-meal sugar rise in some studies, one 6-week placebo-controlled trial saw fasting glucose and HbA1c improve, and another of the same length did not see the after-meal benefit. Promising, unproven.

Back to Table of Contents

Part Two: How Glutamine Actually Works — a Gut Signal

If glutamine lowers blood sugar, the next question is how. The research groups who ran these trials were not testing the glucosamine idea at all. They were testing a gut hormone.

The lining of the intestine contains scattered L-cells that sense nutrients and release GLP-1 (glucagon-like peptide-1) — the same hormone that a well-known class of modern diabetes drugs imitates. GLP-1 tells the pancreas to release more insulin when sugar arrives, and slows the stomach. Tolhurst and colleagues studied L-cells taken from mice and found that, of the amino acids they tested, glutamine was the most effective trigger of GLP-1 release: it raised secretion 1.9-fold, by raising both calcium and cyclic AMP inside the cell.

The human trials line up with that: in Greenfield 2009 and Samocha-Bonet 2011 and 2015, glutamine raised GLP-1 and insulin. Chang 2013 added a second gut mechanism. Glutamine stimulated the pylorus (the valve at the stomach's exit), and because glucose did not fall when the stomach was bypassed, the authors concluded that slowed stomach emptying is probably a major reason glucose falls when glutamine is swallowed before a meal.

Both routes — the GLP-1 signal and the slower stomach — happen in the gut, within minutes of a dose, before any glutamine could matter for glucosamine production inside tissues. Neither has anything to do with turning glucose into glucosamine.

Back to Table of Contents

Why the Glucosamine Pathway Cannot Be a Glucose Drain

Suppose we ignore the gut and ask the question directly: could extra glutamine push enough glucose down the hexosamine pathway to lower blood sugar? Three facts say no.

1. The branch is small. Buse's review describes it as "a relatively minor branch of glycolysis"; the commonly cited estimate, from Marshall's 1991 work in fat cells and quoted in the full text of Buse's review, is that only about 3% of the glucose entering a cell takes this route. The other 97% or so is burned for energy or stored. Even a large increase in a 3% side road moves little of the total.

2. The gate closes itself. GFAT is regulated by the pathway's own end product. Buse notes that UDP-GlcNAc "regulates flux through HBP by regulating GFAT activity." Ruegenberg and colleagues solved the crystal structure of human GFAT-1 in 2020 and showed that UDP-GlcNAc binds the enzyme directly and inhibits it. When the cell has enough of the end product, the gate shuts. Only a mutant enzyme that had lost this feedback (studied in worms and mammalian cells) let the pathway run wide open. Adding more of one raw material — glutamine — does not override a gate that is set by demand.

3. The body only needs so much glucosamine. The end product is used to build sugar chains on proteins and fats. Cells make what they use. There is no store that fills up with surplus glucosamine the way glycogen fills up with surplus glucose.

Put together: the pathway is too narrow, and too tightly controlled, to act as a sugar sink. That step of the idea does not survive testing.

Back to Table of Contents

The Twist: More Hexosamine Flow Is the Insulin-Resistance Signal

There is a deeper problem. Suppose the pathway could be forced open. The research says that would make blood sugar control worse, not better.

The hexosamine pathway is widely thought to act as the cell's glucose sensor. When too much glucose is pouring in, more of it flows down the side road, and the rising end product tells the cell to stop taking in so much glucose — that is, to become insulin resistant. Marshall, Garvey and Traxinger summarised it in 1991 as "a glucose sensor coupled to a negative feedback system that can limit the extent of glucose uptake."

• Glutamine was part of the problem in the original experiment. Marshall, Bacote and Traxinger (1991) found that, in fat cells grown in the laboratory, desensitization of the insulin-responsive glucose transport system required three things together: glucose, insulin and glutamine. Blocking GFAT with drugs prevented it. Glucosamine itself, which enters the pathway past the GFAT gate, produced a 40–50% loss of insulin responsiveness and was estimated to be at least 40 times more potent than glucose at doing so.
• Excess flow causes insulin resistance in animals. McClain and Crook's 1996 review summarised that "excess hexosamine flux causes insulin resistance in cultured cells, tissues, and intact animals."
• Turning up GFAT in mice did exactly that. Hebert and colleagues made mice with 2.4-fold more GFAT activity in muscle. Their glucose disposal rate under insulin fell to 68.5 versus 129.4 mg/kg per minute in normal littermates — roughly half.

This is the core of the matter. The owner's idea is that "using glucose to make glucosamine" would help. But more traffic through that exact route is what cells read as "too much sugar — shut the door." If glutamine really worked by filling the hexosamine pathway, it would be expected to worsen insulin resistance.

In fairness, Buse's review also notes that while many papers show a correlation between increased hexosamine flow and insulin resistance, the causal role in humans "has not been established." The point stands regardless: nothing in this literature suggests that pushing glucose into the pathway is a way to lower blood sugar.

Notice the contrast with glucosamine pills. Glucosamine skips the GFAT gate entirely, which is why it is the potent one in the cell experiments. Glutamine, by contrast, has to pass through the self-limiting gate — and its blood-sugar benefit appears to come from the gut instead. That is good news for glutamine, but for a different reason than the hypothesis proposed.

Back to Table of Contents

Glutamine vs Glucosamine, Side by Side

Back to Table of Contents

Cautions Before Anyone Tries Glutamine

• The doses are big. The trials used 15 to 30 grams a day — several heaped spoonfuls of powder, not a capsule. That is a lot of a single amino acid, and nobody has studied it for longer than about six weeks in diabetes.
• Blood changes were seen. In the 4-week Samocha-Bonet 2014 trial, blood urea rose, and red cells, hemoglobin, hematocrit and albumin fell modestly; the authors interpreted this as mild expansion of plasma volume. Creatinine and eGFR were unchanged.
• Kidney or liver disease. Glutamine carries nitrogen, and the body disposes of nitrogen as urea through the liver and kidneys. Given the rise in urea seen above, the research raises a concern about high-dose glutamine for people with kidney or liver disease, and there is no good safety data on it in those groups. This concern rests on the chemistry, not on a measured harm.
• It raises glucagon too. Greenfield 2009 and Samocha-Bonet 2011 both saw glucagon rise, and Chang 2013 suspected glucagon cancelled out the glucose-lowering effect when the stomach was bypassed.
• It is not a diabetes treatment. No trial has shown it prevents diabetes complications, and no trial has tested it as a replacement for prescribed treatment. For people on diabetes medication, adding anything that lowers glucose can change how the medication behaves — a question that belongs with a clinician.
• For people already taking glucosamine, especially alongside diabetes drugs or warfarin, blood glucose, HbA1c and any change to the routine are questions worth raising with a clinician.

Back to Table of Contents

Food First: Where Glutamine Comes From

The body makes most of its own glutamine (see Endogenous Glutamine Synthesis), and the rest comes from ordinary protein. Every whole-food protein contains it, because glutamine and its close relative glutamate are among the most common amino acids in food protein. Samocha-Bonet 2015 is a useful reminder here: a meal's worth of whole protein did as well as glutamine powder at restoring the early insulin response.

• Meat and fish — beef, chicken, salmon, sardines.
• Eggs and full-fat dairy — eggs, milk, yogurt and cheese.
• Beans and lentils — beans, lentils, chickpeas; these also bring fiber that slows sugar absorption (see Beans for Blood Sugar). Among soy foods, the fermented ones — natto, miso, tempeh — belong in this group.
• Cabbage — cabbage is a traditional vegetable source; fermented as sauerkraut it keeps well.
• Bone broth — a traditional protein food; see Bone Broth and Bone Broth and Glutamine.

Eating protein at the start of a meal is also a simple, food-based version of what the trials did with powder: protein triggers gut hormones and slows the stomach. More on food amounts is on Glutamine Sources.

Back to Table of Contents

The Verdict

The idea is half right. Between the two supplements, glutamine has the better human evidence for blood sugar: several small trials in type 2 diabetes found that glutamine with a meal raised GLP-1 and insulin and blunted the after-meal glucose rise, and one 6-week placebo-controlled trial saw fasting glucose and HbA1c improve. Glucosamine has no such evidence and some signals in the other direction.

But the reason is not the one proposed. Glutamine works through the gut — GLP-1 from L-cells and a slower stomach — not by draining glucose into glucosamine. The hexosamine pathway takes only a small share of glucose, its gate is held shut by its own end product, and in cells and animals more flow through it is the signal that causes insulin resistance.

And it is not a proven diabetes treatment. The doses were large, the trials small and short, the biggest after-meal trial was negative, and blood urea rose in one study. The body's ordinary source of glutamine is whole-food protein at each meal, from meat, fish, eggs, dairy, beans and cabbage. Decisions about glutamine powder — especially with diabetes, kidney or liver disease, or on glucose-lowering drugs — belong with a clinician.

Back to Table of Contents

Key Research Papers

1. Marshall S, Bacote V, Traxinger RR. Discovery of a metabolic pathway mediating glucose-induced desensitization of the glucose transport system. Role of hexosamine biosynthesis in the induction of insulin resistance. J Biol Chem. 1991;266(8):4706-12. — PubMed PMID: 2002019
2. Marshall S, Garvey WT, Traxinger RR. New insights into the metabolic regulation of insulin action and insulin resistance: role of glucose and amino acids. FASEB J. 1991;5(15):3031-6. — doi:10.1096/fasebj.5.15.1743436 (PubMed PMID: 1743436)
3. McClain DA, Crook ED. Hexosamines and insulin resistance. Diabetes. 1996;45(8):1003-9. — doi:10.2337/diab.45.8.1003 (PubMed PMID: 8690144)
4. Hebert LF Jr, Daniels MC, Zhou J, et al. Overexpression of glutamine:fructose-6-phosphate amidotransferase in transgenic mice leads to insulin resistance. J Clin Invest. 1996;98(4):930-6. — doi:10.1172/JCI118876 (PubMed PMID: 8770864)
5. Milewski S. Glucosamine-6-phosphate synthase—the multi-facets enzyme. Biochim Biophys Acta. 2002;1597(2):173-92. — doi:10.1016/s0167-4838(02)00318-7 (PubMed PMID: 12044898)
6. Ruegenberg S, Horn M, Pichlo C, et al. Loss of GFAT-1 feedback regulation activates the hexosamine pathway that modulates protein homeostasis. Nat Commun. 2020;11(1):687. — doi:10.1038/s41467-020-14524-5 (PubMed PMID: 32019926)
7. Buse MG. Hexosamines, insulin resistance, and the complications of diabetes: current status. Am J Physiol Endocrinol Metab. 2006;290(1):E1-E8. — doi:10.1152/ajpendo.00329.2005 (PubMed PMID: 16339923)
8. Tolhurst G, Zheng Y, Parker HE, et al. Glutamine triggers and potentiates glucagon-like peptide-1 secretion by raising cytosolic Ca2+ and cAMP. Endocrinology. 2011;152(2):405-13. — doi:10.1210/en.2010-0956 (PubMed PMID: 21209017)
9. Greenfield JR, Farooqi IS, Keogh JM, et al. Oral glutamine increases circulating glucagon-like peptide 1, glucagon, and insulin concentrations in lean, obese, and type 2 diabetic subjects. Am J Clin Nutr. 2009;89(1):106-113. — doi:10.3945/ajcn.2008.26362 (PubMed PMID: 19056578)
10. Samocha-Bonet D, Wong O, Synnott EL, et al. Glutamine reduces postprandial glycemia and augments the glucagon-like peptide-1 response in type 2 diabetes patients. J Nutr. 2011;141(7):1233-8. — doi:10.3945/jn.111.139824 (PubMed PMID: 21593352)
11. Samocha-Bonet D, Chisholm DJ, Gribble FM, et al. Glycemic effects and safety of L-Glutamine supplementation with or without sitagliptin in type 2 diabetes patients—a randomized study. PLoS One. 2014;9(11):e113366. — doi:10.1371/journal.pone.0113366 (PubMed PMID: 25412338)
12. Samocha-Bonet D, Chisholm DJ, Holst JJ, et al. L-glutamine and whole protein restore first-phase insulin response and increase glucagon-like peptide-1 in type 2 diabetes patients. Nutrients. 2015;7(4):2101-8. — doi:10.3390/nu7042101 (PubMed PMID: 25811109)
13. Chang J, Wu T, Greenfield JR, et al. Effects of intraduodenal glutamine on incretin hormone and insulin release, the glycemic response to an intraduodenal glucose infusion, and antropyloroduodenal motility in health and type 2 diabetes. Diabetes Care. 2013;36(8):2262-5. — doi:10.2337/dc12-1663 (PubMed PMID: 23564914)
14. Mansour A, Mohajeri-Tehrani MR, Qorbani M, et al. Effect of glutamine supplementation on cardiovascular risk factors in patients with type 2 diabetes. Nutrition. 2015;31(1):119-26. — doi:10.1016/j.nut.2014.05.014 (PubMed PMID: 25466655)
15. Mansour A, Mohajeri-Tehrani MR, Qorbani M, et al. Postprandial glycemia and insulin secretion following glutamine administration: a randomized controlled trial. Int J Vitam Nutr Res. 2020;90(5-6):425-429. — doi:10.1024/0300-9831/a000463 (PubMed PMID: 32729784)
16. Cheng S, Rhee EP, Larson MG, et al. Metabolite profiling identifies pathways associated with metabolic risk in humans. Circulation. 2012;125(18):2222-31. — doi:10.1161/CIRCULATIONAHA.111.067827 (PubMed PMID: 22496159)
17. Monauni T, Zenti MG, Cretti A, et al. Effects of glucosamine infusion on insulin secretion and insulin action in humans. Diabetes. 2000;49(6):926-35. — doi:10.2337/diabetes.49.6.926 (PubMed PMID: 10866044)
18. Pham T, Cornea A, Blick KE, et al. Oral glucosamine in doses used to treat osteoarthritis worsens insulin resistance. Am J Med Sci. 2007;333(6):333-9. — doi:10.1097/MAJ.0b013e318065bdbe (PubMed PMID: 17570985)
19. Muniyappa R, Karne RJ, Hall G, et al. Oral glucosamine for 6 weeks at standard doses does not cause or worsen insulin resistance or endothelial dysfunction in lean or obese subjects. Diabetes. 2006;55(11):3142-50. — doi:10.2337/db06-0714 (PubMed PMID: 17065354)
20. Dostrovsky NR, Towheed TE, Hudson RW, et al. The effect of glucosamine on glucose metabolism in humans: a systematic review of the literature. Osteoarthritis Cartilage. 2011;19(4):375-80. — doi:10.1016/j.joca.2011.01.007 (PubMed PMID: 21251987)

PubMed Topic Searches

1. PubMed: glutamine, GLP-1 and type 2 diabetes
2. PubMed: oral glutamine and post-meal blood sugar
3. PubMed: hexosamine pathway and insulin resistance
4. PubMed: GFAT feedback inhibition by UDP-GlcNAc

This content is provided for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before beginning or stopping any supplement.

Back to Table of Contents

Connections

• All Amino Acids
• Glucosamine
• How the Body Makes Glucosamine
• Glucosamine, Blood Sugar and Diabetes
• Glucosamine for Joint Pain
• Glucosamine Safety
• History of Glucosamine
• Glutamine
• Endogenous Glutamine Synthesis
• Glutamine Benefits
• Glutamine Sources
• Type 2 Diabetes
• Insulin Resistance
• Blood Sugar
• Hemoglobin A1C (Lab Test)
• HOMA-IR (Lab Test)
• Beans for Blood Sugar
• Cabbage
• Bone Broth
• Blood Sugar & Insulin — interactive animation
• Insulin Signaling & GLUT4 — interactive animation

Back to Table of Contents

Featured Videos