IngredientsGlycomacropeptide (GMP) is the C-terminal part (residues 106–169) of kappa-casein, which is released into whey during cheese making by the action of chymosin. GMP is a bioactive peptide derived from whey protein, consisting of 64 amino acids. The compound is known by several synonyms, including caseinomacropeptide (CMP), casein macropeptide (CM), and casein derived peptide (CDP). The unglycosylated form is specifically known as caseinomacropeptide or CMP. In the context of phenylketonuria (PKU) management, the supplemented, amino-acid-enriched form is frequently abbreviated as CGMP-AA.
Glycomacropeptide is a milk-derived phosphorylated glycopeptide consisting of 64 amino acids. GMP is highly polar and is glycosylated by galactosamine, galactose, and O-sialic acid at one or more threonine amino acid sites. GMP exists as a mixture of different glycoforms due to the carbohydrates sialic acid (N-acetylneuraminic acid, NeuNAc), galactose, galactosamine, and glucosamine attached by O-glycosidic linkages. GMP contains three primary phosphorylation sites located on serine residues. Glycosylation of GMP at threonine residues via O-H linkages occurs with five different mucin-type carbohydrate chains containing N-acetylneuraminic acid (sialic acid), galactose, or N-acetylgalactosamine.
When the pH of a solution of GMP is less than 4, the molecular weight is approximately 9,000 Da. When the pH is greater than 4, the GMP apparent molecular weight increases to approximately 45,000 Da. The characteristic molecular weight of the unassociated peptide backbone alone is approximately 6,780 Da, as determined by mass spectrometry. GMP protein contains 47% (w/w) indispensable amino acids, but contains no histidine, tryptophan, tyrosine, arginine, cysteine, or phenylalanine in its pure form.
GMP carries all of the carbohydrate groups of the parent κ-casein protein. κ-casein is the only casein protein which is glycosylated.
Glycomacropeptide is a glycosylated peptide formed during renneting as a fragment of sweet whey. Acid whey from yogurt or curdling cheese without the use of rennet does not contain GMP. GMP is formed during cheese making when chymosin specifically cleaves κ-casein between the 105th and 106th amino acid residues. Para-κ-casein (residues 1 to 105) coagulates, forming cheese curd, while GMP (residues 106 to 169) remains in the whey.
GMP is a milk-derived bioactive peptide that comprises 15–20% of proteins present in whey, being the third most abundant. It is released from κ-casein by enzymatic digestion, either physiologically or in industry during the cheese making process. Although GMP is released from κ-casein during cheese making by the action of rennet, smaller concentrations of GMP also exist in bovine milk. However, GMP released from casein is almost ten times higher than free GMP in mature milk.
Both GMP and CMP exist in roughly similar amounts in whey. Together, GMP and CMP make up 20–25% of whey protein, making them the third largest fraction of whey protein isolate, after alpha-lactalbumin and beta-lactoglobulin.
GMP is commercially available in several purified forms. GMP can be isolated from whey protein isolate (WPI) by three primary methods: trichloroacetic acid (TCA) fractionation, ethanol precipitation, and ultrafiltration. TCA pretreatment recovered only sialo-GMP (glycosylated fractions) and eliminated contaminating proteins; ethanol precipitation recovered GMP from WPI with approximately 75.7% glycosylation; ultrafiltration was found to be the most effective method in recovering GMP.
At pH 3.5, GMP permeates through ultrafiltration membranes with a molecular weight cut-off ranging from 20 to 50 kDa, while the majority of whey proteins such as β-lactoglobulin, α-lactalbumin, immunoglobulins, and bovine serum albumin are retained. This property forms the basis of many industrial purification processes. In the context of medical nutrition, GMP is formulated as a powdered medical food, typically mixed with water or incorporated into food products. Commercial preparations such as Lacprodan® CGMP-20 and Lacprodan® CGMP-30 are highly purified casein glycomacropeptide ingredients with a very low content of phenylalanine and tyrosine.
Besides its biological activity, GMP has several techno-functional properties such as wide pH-range solubility, emulsifying properties, and foaming abilities, which are promising for applications in the food and nutrition industry.
GMP is not a traditional herbal or botanical remedy with a history of deliberate medicinal use by pre-modern cultures. As a peptide released specifically during enzymatic (rennet-based) cheese making, its identity as an isolatable, bioactive compound was not recognized until the modern era of biochemical analysis. GMP as a distinct chemical entity was characterized following the elucidation that it is formed by the cleavage of κ-casein between Phe105 and Met106 by the action of rennet during cheese manufacture. It took many years after this discovery before GMP was taken as a new product opportunity, as GMP preparations until the early 1990s were not pure enough to replace synthetic amino acid mixtures in the management of phenylketonuria and severe liver disease.
The precursor to GMP—sweet cheese whey—has a much longer history as a food and incidental health remedy. Whey has been consumed in European and Middle Eastern cultures for centuries as a byproduct of cheese making, valued for its nutritional content. However, the specific bioactive peptide GMP was neither isolated, identified, nor intentionally administered during those periods. The deliberate scientific investigation of GMP as a bioactive ingredient began in earnest in the 1970s–1990s, following the first complete sequencing of κ-casein and the development of refined chromatographic separation techniques. Bovine glycomacropeptide is a natural milk peptide that is produced naturally in the gastrointestinal tract during digestion, suggesting that humans have been exposed to GMP as an endogenous digestive product whenever milk-based cheese was consumed, but awareness of this phenomenon is entirely a product of 20th-century biochemistry.
Glycosylation of GMP at threonine residues via O-H linkages occurs with five different mucin-type carbohydrate chains containing sialic acid, galactose, or N-acetylgalactosamine. Approximately 75% of glycosylated GMP molecules include trisaccharide and tetrasaccharide chains. The most abundant oligosaccharide structure features N-acetylgalactosamine (GalNAc) O-linked to serine or threonine, which in turn is bonded to sialic acid (N-acetylneuraminic acid) and galactose via α-2,6 and β-1,3 glycosidic bonds.
Concentrations of isoleucine and threonine in GMP are 2- to 3-fold greater, respectively, than those found in other dietary proteins. GMP protein contains 47% (w/w) indispensable amino acids but contains no histidine, tryptophan, tyrosine, arginine, cysteine, or phenylalanine. This unique amino acid profile is of particular nutritional interest because of GMP's near-absence of phenylalanine (Phe), making it relevant to the dietary management of phenylketonuria.
GMP is a bioactive peptide derived from milk κ-casein that contains abundant sialic acid and has shown anti-inflammatory, antioxidative, anti-obesity, and anti-diabetic properties when orally administered. Sialic acid residues on GMP have been proposed to mediate some of its biological activities; however, studies of GMP in activated human macrophages showed similar effects when cells were pretreated with asialo-GMP (GMP stripped of sialic acid), with no change in the gene expression of lectins associated with sialic acid recognition, suggesting that sialic acid might not be involved in this immunoregulatory effect and that GMP exerts anti-inflammatory and antioxidative activities on activated macrophages in a sialic acid-independent manner.
GMP exists in two primary genetic variants: GMP variant A and GMP variant B, which are the two major genetic variants of GMP. Many of the biological properties have been ascribed to the carbohydrate moieties attached to the peptide. The degree of glycosylation varies; the unglycosylated form is known as caseinomacropeptide (CMP), and both forms exist in roughly similar amounts in whey.
GMP was shown under in vitro and in vivo conditions to exert a number of activities that regulate the physiology of important body systems, namely the gastrointestinal, endocrine, and immune systems. One of the most studied mechanisms is the stimulation of cholecystokinin (CCK). GMP reportedly stimulates the release of cholecystokinin (CCK), which may promote satiety. Interest in the intake regulatory effect of caseinomacropeptide arises from its known actions on gastrointestinal function and the release of the satiety gut hormone CCK. CMP inhibits gastric acid secretions in calves, while a fraction of CMP, variant A with slight glycosylation, has been shown to stimulate CCK release in rats.
Analysis of pathways involved in LPS-induced Toll-like receptor 4 (TLR4) activation showed that GMP hydrolysate (GMPH) diminished the increase in TLR4 and MyD88 mRNA expression levels, blocked p65 nuclear translocation, and inhibited phosphorylation and degradation of IκBα and phosphorylation of IKKα/β, stimulated by LPS in macrophages. This NF-κB pathway inhibition constitutes one of the principal identified molecular mechanisms by which GMP suppresses pro-inflammatory cytokine production. GMP pretreatment decreased by 35%, 35%, and 49% the production of nitrites, interleukin (IL)-1β, and tumor necrosis factor (TNF)-α, respectively, in activated human macrophages (U937 cell line).
The intestinal anti-inflammatory action of GMP is proposed to be mediated by direct modulation of monocyte or splenocyte activity, especially by hampering the activation of T helper 1 (Th1) cells while favoring the differentiation of regulatory T (Treg) cells.
GMP has been shown to bind and inactivate toxins of Escherichia coli and Vibrio cholerae and inhibit the adhesion of cariogenic bacteria. GMP is a putative prebiotic based on this high degree of glycosylation, meaning its carbohydrate moieties may serve as fermentation substrates for beneficial intestinal bacteria. In mouse models, cecal concentrations of the short-chain fatty acids (SCFA) acetate, propionate, and butyrate were increased with GMP feeding. The percentage of stimulated spleen cells producing interferon-γ (IFN-γ) was significantly reduced in mice fed GMP compared with casein, and plasma concentrations of IFN-γ, TNF-α, IL-1β, and IL-2 were reduced.
The addition of GMP as an active component to different products showed that it inhibits the adhesion to surface plastic of bacteria that induce dental plaque and caries, such as Streptococcus mutans, S. sanguis, and Actinomyces viscosus. Likewise, the incorporation of GMP into salivary films modified the adherence of S. sobrinus and S. mutans to bovine enamel discs. These effects are believed to occur through competitive inhibition of bacterial adhesion at oral surfaces.
CGMP has a high content of large neutral amino acids (LNAA), such as threonine and isoleucine. These LNAAs compete with phenylalanine when crossing the blood-gut barrier and the blood-brain barrier, helping to prevent toxic levels of phenylalanine from accumulating in the brain.
Normal intake of dietary protein in untreated PKU causes phenylalanine (Phe) to accumulate in blood, leading to toxic concentrations of Phe in the brain and the devastating phenotype of profound cognitive impairment. The primary therapy for PKU is lifelong adherence to a low-Phe diet that limits Phe intake from natural foods that contain protein, and traditionally, supplementation with amino acid-based medical foods (AA-MFs) to provide the majority of dietary nitrogen and micronutrients. Lifelong compliance with the PKU diet is poor, and there is evidence of suboptimal health outcomes in patients using AA-MFs, including neurocognitive impairment, skeletal fragility, and impaired renal function.
GMP is a phenylalanine-free peptide, making it a beneficial dietary option for individuals dealing with phenylketonuria. PKU is an inherited metabolic disorder characterized by high levels of phenylalanine in the bloodstream, resulting from a deficiency of phenylalanine hydroxylase.
A 2-stage, randomized crossover trial included 30 early-treated PKU subjects (aged 15–49 years), 20 with classical and 10 with variant PKU. Subjects consumed, in random order for 3 weeks each, their usual low-Phe diet combined with AA-MFs or GMP-MFs. Clinical evaluation in 11 PKU subjects who participated in an inpatient metabolic study demonstrated safety, acceptability, improved satiety, and greater protein retention with GMP-MFs than with AA-MFs, and provided evidence to optimize supplementation of glycomacropeptide with limiting amino acids.
In phenylketonuria, modified casein glycomacropeptide supplements (CGMP-AA) are used as an alternative to the traditional phenylalanine-free L-amino acid supplements. However, studies focusing on the long-term nutritional status of CGMP-AA are lacking. One retrospective study evaluated the long-term impact of CGMP-AA over a mean of 29 months in 11 patients with a mean age at CGMP-AA onset of 28 years. CGMP-AA, providing 66% of protein equivalent intake from protein substitute, was associated with no significant change in blood Phe compared with baseline (562 ± 289 µmol/L vs 628 ± 317 µmol/L; p = 0.065).
Preclinical studies in the PKU mouse model established that glycomacropeptide supplemented with limiting amino acids supports growth and reduces concentrations of Phe in plasma and brain, improves bone status, and attenuates metabolic stress compared with an amino acid diet.
A 2019 randomized controlled crossover trial in children with PKU investigated whether CGMP-AA reduces blood Phe variability compared to L-amino acids. Evidence suggests that casein glycomacropeptide supplemented with rate-limiting amino acids (CGMP-AA) is associated with better protein utilisation and less blood phenylalanine variability.
The use of CGMP compared to mono amino acids (L-AAs) as a protein substitute in the treatment of PKU promises several potential clinical benefits, although any advantage is supported only by evidence from non-PKU conditions or PKU animal models. Overall, the clinical evidence for GMP in PKU management is preliminary to moderate in strength, derived primarily from small crossover trials and retrospective studies; larger, long-term randomized controlled trials are still needed.
GMP is a peptide that has been shown to stimulate release of cholecystokinin, which may promote satiety. A one-year study examined whether greater weight loss could be achieved and sustained with a GMP-enriched whey powder supplement compared with a skim milk powder supplement, using a double-blind, randomized, parallel-design study. Meal replacements contained 15 g protein from GMP-enriched whey protein isolate (GMP-WPI) or skim milk powder (SMP) and 900 kJ/sachet. Volunteers consumed 2 sachets per day instead of 2 meals for 6 months and then 1 sachet per day for a further 6 months.
Clinical research suggests that replacing one or two meals daily with a meal-replacement supplement containing glycomacropeptide for one year while also following an energy-restricted diet reduces weight by approximately 24 lbs compared to baseline. However, the effect of the glycomacropeptide supplement does not appear to be different from taking a similar skim milk powder supplement. This indicates that any weight-loss effect observed was not specific to GMP.
A randomized double-blind acute study in twenty overweight/obese males recruited to consume four 50-g preloads including minimally glycosylated GMP, glycosylated GMP, a GMP-depleted whey protein concentrate, and glucose, followed by blood sampling and subjective satiety measures at multiple time points, and a lunch meal. There was no significant difference in CCK levels, subjective measures of satiety, or food intake between treatments at the given preload level, suggesting that the protein fractions at the dose employed do not influence satiety, CCK levels, or energy intake at a subsequent meal.
Test meal intake was not different by preload; however, compensation relative to usual daily intake was achieved after whey-containing and GMP-containing preloads in women. GMP alone is not critical in pre-meal whey-induced satiety; however, it may have a unique role in compensatory intake regulation managing daily energy intake.
Evidence strength: Human clinical evidence for GMP as a standalone satiety or weight-loss agent is weak and inconsistent. While animal and in vitro studies suggest CCK-stimulating effects, human trials have not demonstrated a specific, reproducible advantage of GMP over other comparable protein sources in controlling satiety or promoting weight loss.
Previous laboratory studies identified two dairy fractions, GMP and G600 milk fat extract, with anti-inflammatory effects in models of acute gout. A proof-of-concept, 3-month, randomized double-blind controlled trial enrolled 120 patients with recurrent gout flares, randomized to one of three arms: lactose powder control, skim milk powder (SMP) control, and SMP enriched with GMP and G600 (SMP/GMP/G600).
In this trial, the SMP/GMP/G600 group received GMP at 1.5 grams per day and 0.525 grams per day of G600 milk fat extract. Over the 3-month study period, there was a significantly greater reduction in gout flares in the SMP/GMP/G600 group (ANCOVA p(group) = 0.031; Tukey post hoc test vs. lactose control, p = 0.044). Following treatment with SMP/GMP/G600 over the 3-month period, greater improvements were also observed in pain and fractional excretion of uric acid, with trends toward greater improvement in tender joint count.
The frequency of acute gout attacks, measured as the number of flares per month, decreased in all three groups over the three-month study period, complicating interpretation of GMP-specific effects. A Cochrane-style review found no high-quality evidence that supported or refuted the use of glycomacropeptide-enriched skim milk powder for adults with chronic gout.
Evidence strength: Preliminary. There is a single proof-of-concept RCT (n=120) suggesting possible benefit in reducing gout flare frequency when GMP is combined with G600 milk fat extract; the effect was statistically significant versus lactose control, but all groups including controls improved, and no high-quality evidence exists to confirm clinical benefit from GMP alone.
Studies demonstrated that orally administered GMP to rats exerts an anti-inflammatory effect in colitis and ileitis induced with trinitrobenzenesulfonic acid (TNBS), or in colitis induced by dextran sulfate sodium (DSS), with a degree of efficacy in some assays similar to that of sulfasalazine, a drug widely used in the therapy of IBD. Healthy and PKU mice receiving a GMP-enriched diet for eight weeks showed modification of the intestinal bacterial population by reducing the Proteobacteria phylum, especially Desulfovibrio sp., both in cecal content and feces — microorganisms associated with the pathogenesis of inflammatory bowel disease.
In a rat ovalbumin-induced food allergy model, oral GMP intake decreased clinical signs and diarrhea severity induced by allergen, with a significant reduction in intestinal edema and expression levels of IL-1β and TNF-α.
A pilot clinical study assessed alterations in gut microbiota composition, fecal and blood inflammatory markers, and gut-related symptoms before, during, and after a GMP feeding period in adult IBS subjects. The results revealed no changes in fecal microbiota, subtle effects on systemic and intestinal immune markers, and no changes in gut-related symptoms during and after the GMP supplementation.
Initial research suggests that GMP might play a significant role in IBS management by potentially influencing gut microbiome dynamics, immune responses, and gut motility and barrier functions. It is hypothesized that GMP consumption might alter the gut microbiota by encouraging the growth of beneficial bacterial species, although more research is needed to confirm these findings. Furthermore, GMP may hold the potential to attenuate inflammatory responses commonly observed in IBS, possibly through the modulation of cytokine concentrations and the enhancement of intestinal short-chain fatty acid production.
Evidence strength: The anti-inflammatory and IBD-related evidence for GMP in humans is largely absent or very preliminary. Substantial preclinical (animal and cell-based) data supports anti-inflammatory mechanisms, but clinical translation has not yet been established in controlled human trials. The IBS pilot study showed no significant improvements in primary endpoints.
The main biological activities of GMP with health-beneficial properties are antibacterial, prebiotic, remineralizing, modulation of digestion and metabolism, anti-tumoral, and immuno-modulation activities. At the cellular level, studies using human THP-1 cells as an in vitro monocyte model assessed the effect of bovine GMP on the secretion of TNF, IL-1β, and IL-8, as well as the involvement of the NF-κB and MAP kinase signaling pathways.
In an in vitro atopic dermatitis model, studies evaluated the effect of GMP on the inflammatory, oxidative, proliferative, and migratory responses of HaCaT keratinocytes. GMP protected keratinocytes from death and apoptosis in a dose-dependent manner. GMP at 6.3 and 25 mg/mL reduced nitric oxide by 50% and 83.2%, as well as lipid hydroperoxides by 27.5% and 45.18% in activated HaCaT cells.
Evidence strength: Primarily in vitro and animal. There is consistent mechanistic evidence that GMP modulates innate immune pathways (NF-κB, MAPK, cytokine production) in cell and animal models. Human clinical data confirming immunomodulatory benefit in specific conditions is limited.
Health-promoting activities of this whey peptide include antimicrobial and anticariogenic properties. GMP has shown anti-cariogenic activity. The addition of GMP as an active component to different products inhibited the adhesion to surface plastic of bacteria that induce dental plaque and caries, such as Streptococcus mutans, S. sanguis, and Actinomyces viscosus. GMP has been shown to bind and inactivate toxins of Escherichia coli and Vibrio cholerae and inhibit the adhesion of cariogenic bacteria.
Evidence strength: Preclinical (in vitro) only. No human clinical trials have been reported specifically testing GMP as a caries-prevention agent in oral health settings.
GMP is a 64-amino acid glycophosphopeptide with application to the nutritional management of PKU, obesity, and inflammatory bowel disease. GMP is a putative prebiotic based on extensive glycosylation with sialic acid, galactose, and galactosamine. GMP is a prebiotic based on reduction in Desulfovibrio, increased short-chain fatty acids, and lower indexes of inflammation compared with casein and amino acid diets in mice. Functional foods made with GMP may be beneficial in the management of PKU, obesity, and IBD.
Evidence strength: Primarily animal-based. The human pilot study on IBS showed no significant changes in fecal microbiota composition. Preclinical evidence from mouse models supports a prebiotic mechanism, but this has not been confirmed in controlled human studies.
GMP is available as a purified powder, frequently formulated into medical foods (powders that are dissolved in water or incorporated into food preparations). In the weight-management trial, meal replacements contained 15 g protein from GMP-enriched whey protein isolate (GMP-WPI) or skim milk powder per sachet (900 kJ); volunteers consumed 2 sachets per day (replacing 2 meals) for the first 6 months and 1 sachet per day for a further 6 months.
In the gout trial, the SMP/GMP/G600 group received GMP at a dose of 1.5 grams per day, combined with 0.525 grams per day of G600 milk fat extract, over a three-month period.
In the PKU randomized crossover trial (n=30 subjects, aged 15–49 years), subjects consumed their usual low-Phe diet combined with AA medical foods or GMP medical foods for 3 weeks each. Protein equivalents provided by GMP-based medical foods in PKU studies are typically calculated on the basis of individual protein requirements per clinical guidelines for each patient. In one retrospective study, CGMP-AA provided 66% of protein equivalent intake from protein substitute, evaluated over a mean of 29 months.
In the CCK/satiety study, three GMP glycoforms were tested: minimally glycosylated GMP (3.5% NeuNAc and 1.5% Gal), fully glycosylated GMP (12.0% NeuNAc and 4.2% Gal), and a GMP-depleted whey protein concentrate, each administered as a 50 g preload.
No official dosage recommendations from pharmacopeial bodies (USP, European Pharmacopoeia) or governmental health agencies (NIH, EFSA, EMA) have been established for GMP as a general dietary supplement in healthy individuals. The appropriate dose of glycomacropeptide depends on several factors such as the user's age, health, and several other conditions, and at this time there is not enough scientific information to determine an appropriate range of doses.
When taken by mouth, glycomacropeptide is possibly safe when taken as a food supplement for up to one year. In the gout flare trial, similar adverse event rates and discontinuation rates were observed between the GMP-enriched and control groups, supporting short-term tolerability. Clinical evaluation of glycomacropeptide in 11 PKU subjects demonstrated safety and acceptability with GMP medical foods.
Glycomacropeptide is not a complete protein and contains limiting amounts of the following indispensable amino acids relevant to PKU management: arginine, histidine, leucine, tryptophan, and tyrosine. For this reason, GMP medical foods used in PKU management are always supplemented with these limiting amino acids, and GMP alone should not be used as a sole dietary protein source without appropriate supplementation.
GMP in its pure form contains no phenylalanine. However, commercially produced GMP inevitably contains trace levels of phenylalanine due to contamination with other whey proteins during industrial purification. Consequently, according to European guidelines, CGMP may be used as a protein substitute by patients with PKU above four years of age. Precise Phe content of any specific GMP product must be verified for use in PKU management.
GMP is derived from bovine milk and is therefore contraindicated in individuals with a confirmed allergy to bovine milk proteins or κ-casein. It has been reported that bovine GMP does not induce T cell-mediated immune responses in vivo, unlike the native protein κ-casein, even when administered as a polymer, suggesting a potentially reduced allergenicity relative to the intact parent protein; however, GMP should still be avoided in those with verified dairy protein allergies.
The threonine content of GMP medical foods is approximately twice that of equivalent amino acid medical foods (106 ± 4 mg Thr/g protein equivalents compared with 59 ± 1 mg Thr/g protein equivalents, P < 0.0001), due to the high concentration of threonine within the glycomacropeptide peptide. The metabolic consequences of this elevated threonine intake over very long periods in individuals with metabolic disease have not been fully characterized.
There is not enough reliable information to know if glycomacropeptide is safe to use when pregnant or breastfeeding. Controlled data specifically evaluating GMP safety in these populations are absent from the published literature.
No pharmacokinetic drug interactions involving GMP as a dietary supplement have been identified in the reviewed literature. GMP's mechanism of action involves nutritional and immunomodulatory pathways rather than cytochrome P450 enzyme systems, and no direct interactions with pharmaceutical drugs have been reported in peer-reviewed clinical sources to date.
According to European guidelines, CGMP may be used as a protein substitute by patients with PKU above four years of age. Several pediatric clinical studies have been conducted in PKU populations without reports of serious adverse effects attributable to GMP, though the total body of pediatric safety data remains limited.
Health conditions that Glycomacropeptides may help support.
Body systems that Glycomacropeptides may help support.
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