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GLP-1, GIP, glucagon and amylin dominate much of today’s discussion around metabolic research.
But another signalling system is attracting increasing scientific attention:
GDF15 and its receptor GFRAL.
Growth differentiation factor 15 — usually shortened to GDF15 — is a stress-responsive signalling protein whose biology is very different from traditional incretin hormones.
Researchers are investigating its connections with appetite, energy regulation, cellular stress, liver biology and metabolic disease.
Most interestingly, its receptor is concentrated within a remarkably specific region of the brain.
That makes the GDF15–GFRAL pathway one of the more unusual emerging areas of metabolic science.
What Is GDF15?
GDF15 stands for growth differentiation factor 15.
It is a member of the transforming growth factor-beta, or TGF-β, superfamily.
Unlike a conventional gut hormone released primarily after eating, GDF15 can increase in response to different forms of physiological and cellular stress.
Elevated GDF15 has been observed in numerous biological circumstances.
This means scientists have had to distinguish between GDF15 acting as:
a biological signal
and
a biomarker associated with physiological stress or disease.
These aren’t necessarily the same thing.
What Is GFRAL?
One of the biggest breakthroughs in GDF15 research came when scientists identified its receptor.
The receptor is called:
GDNF family receptor alpha-like — GFRAL.
GFRAL works alongside the co-receptor RET to transmit GDF15 signalling.
But there’s something unusual about GFRAL.
Unlike many metabolic receptors distributed across numerous organs, GFRAL expression is highly concentrated within specific areas of the hindbrain.
These include the area postrema and nucleus of the solitary tract.
This immediately provided researchers with an important clue about how circulating GDF15 could communicate with the brain.
The GDF15–GFRAL Pathway
The basic pathway can be simplified as:
Physiological or cellular stress
↓
GDF15 increases
↓
GDF15 reaches the hindbrain
↓
GFRAL/RET signalling is activated
↓
Changes in feeding and metabolic responses
This represents a very different metabolic signalling architecture from GLP-1 or insulin.
Rather than simply acting as another incretin hormone, GDF15 appears to function partly as a stress-related metabolic messenger.
Why Is GDF15 Connected With Appetite?
Experimental research established that GDF15 signalling through GFRAL can reduce food intake.
Animal studies in which GFRAL was removed or blocked provided particularly important evidence.
Without functional GFRAL signalling, the characteristic effects of experimentally administered GDF15 on food intake and body weight were greatly reduced or absent.
This helped establish GFRAL as the principal receptor responsible for these metabolic effects of GDF15.
Is GDF15 Another GLP-1?
No.
Although both pathways can influence feeding behaviour, their underlying biology is substantially different.
GLP-1 is an incretin hormone closely connected with nutrient intake and gastrointestinal signalling.
GDF15 is more strongly associated with cellular and physiological stress signalling.
Their receptors are also different.
GLP-1 acts through the GLP-1 receptor.
GDF15 acts through the GFRAL/RET receptor complex.
This distinction makes GDF15 particularly interesting to researchers searching for metabolic pathways outside conventional incretin biology.
A Kidney–Brain Connection
Recent research has also highlighted an intriguing relationship between GDF15 and the kidneys.
The kidney can contribute to circulating GDF15 under particular metabolic conditions.
Researchers have consequently proposed a kidney–brain signalling axis in which metabolic signals generated peripherally ultimately influence feeding behaviour through GFRAL-containing neurons in the hindbrain.
This illustrates how metabolic regulation extends far beyond the gastrointestinal tract.
The intestine, pancreas, liver, adipose tissue, skeletal muscle, kidneys and brain all participate in interconnected signalling networks.
GDF15 and Metformin
GDF15 has also attracted attention because research has linked it to some of the metabolic effects associated with metformin.
Experimental studies found that metformin can increase circulating GDF15.
Subsequent work has investigated whether signalling through GFRAL contributes to changes in food intake and body weight observed with metformin.
This discovery demonstrated something broader.
A medicine can produce metabolic effects partly by changing an endogenous signalling molecule rather than simply binding directly to the final receptor involved.
That creates another potential research strategy:
Instead of directly activating a receptor, researchers could potentially influence the body’s own production of metabolic signals.
GDF15 May Do More Than Alter Food Intake
Initially, much of the metabolic interest in GDF15 centred on appetite suppression.
The biology now appears more complicated.
Experimental research has suggested that GDF15 may also influence:
- energy expenditure
- insulin sensitivity
- skeletal-muscle metabolism
- liver biology
- inflammatory signalling
Some of these observations remain predominantly preclinical and shouldn’t automatically be assumed to occur identically in humans.
Nevertheless, they have expanded scientific interest in the pathway considerably.
GDF15 and Energy Expenditure
One particularly interesting area concerns adaptive thermogenesis.
When energy intake decreases and body weight falls, the body can respond by reducing energy expenditure.
This biological adaptation can oppose continued changes in body weight.
Experimental work has suggested that GDF15 may influence energy expenditure through mechanisms involving skeletal muscle.
This raised the possibility that GDF15 biology isn’t explained entirely by reduced food intake.
Researchers are still investigating how important these additional mechanisms are in humans.
GDF15 and the Liver
The liver has become another emerging area of GDF15 research.
Experimental studies have investigated relationships between GDF15 signalling, liver fat, inflammation and metabolic dysfunction.
New research published in 2026 has gone further by examining whether GDF15 can influence liver inflammation independently of changes in body weight.
This is important scientifically.
If confirmed and translated into human biology, it would suggest that some effects associated with the pathway could arise from specific neuroendocrine signalling rather than simply being secondary consequences of reduced energy intake.
The GDF15 Paradox
GDF15 biology also presents researchers with an interesting paradox.
Higher circulating concentrations can occur in several diseases and physiological stress states.
Yet researchers are simultaneously investigating whether manipulating the pathway could have therapeutic applications.
How can both be true?
Because a biological molecule can act as both a response to disease and a regulator of physiology.
Elevated concentrations don’t automatically mean the molecule itself caused the underlying condition.
GDF15 may instead be part of the body’s response to cellular stress.
Understanding this distinction is essential when interpreting biomarker research.
GDF15 and Cachexia
The pathway has another side that makes it particularly complex.
Very high or sustained GDF15 signalling has been associated with anorexia-cachexia syndromes, including those occurring in some cancers.
Cachexia involves involuntary loss of body weight and tissue associated with serious disease.
Consequently, researchers are studying the GDF15 pathway from opposite directions.
In some metabolic contexts, scientists have investigated increasing or mimicking GDF15 signalling.
In cachexia research, scientists have investigated blocking GDF15 signalling.
The same biological pathway can therefore potentially be approached in opposite directions depending on the disease being studied.
Why GDF15 Is Different From Most Current Metabolic Targets
GDF15 illustrates how much broader metabolic science is becoming.
The field isn’t restricted to hormones released following food intake.
Researchers are increasingly examining communication between:
cellular stress
peripheral organs
the nervous system
and
whole-body metabolism.
The highly restricted location of GFRAL within the hindbrain makes this pathway particularly unusual.
A signal produced throughout the body can communicate with a relatively small population of specialised neurons and potentially trigger much broader physiological responses.
Could GFRAL Become a Major Metabolic Target?
It’s too early to know.
Important challenges remain.
GDF15 signalling has associations with nausea, aversive responses and pathological appetite suppression, meaning that simply maximising the pathway would not necessarily be desirable.
Researchers therefore need to understand which effects can be separated, how signalling intensity matters and whether different molecular approaches produce different responses.
This is exactly why the pathway remains scientifically interesting.
Beyond the Incretin Era
The extraordinary growth of GLP-1 research has demonstrated how powerful endocrine signalling pathways can be as research targets.
But metabolic biology contains many more signalling systems.
GDF15–GFRAL represents one of them.
It connects cellular stress, peripheral organs and highly specialised regions of the brain in a way that is fundamentally different from the incretin pathways dominating current metabolic pharmacology.
As scientists learn more about GDF15’s relationships with appetite, energy expenditure, liver biology and systemic metabolism, the pathway could provide important clues about where metabolic research moves next.
The future of the field may therefore involve considerably more than developing increasingly powerful GLP-1 combinations.
It may involve discovering entirely different biological communication systems.
Research Notice: Research involving manipulation of the GDF15–GFRAL pathway remains experimental in many of the contexts discussed above. Preclinical findings should not be assumed to translate directly to humans. This article is provided for scientific and educational purposes only and does not provide medical advice, treatment recommendations or dosing guidance.