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Ghrelin is a 28-amino-acid peptide hormone produced primarily by specialised X/A-like cells in the stomach fundus, and is the only circulating hormone known to directly stimulate appetite and hunger signalling. It rises before anticipated meals, falls after eating, and rises again – more strongly – during caloric restriction and weight loss, including after stopping GLP-1 receptor agonist medications. Ghrelin requires a unique chemical modification – octanoyl acylation at its third serine residue, catalysed by the enzyme GOAT – to bind its receptor and exert its orexigenic effects. Understanding ghrelin goes beyond the simple “hunger hormone” label: it is a metabolic state sensor that integrates energy availability, meal timing, and dietary composition into a single hormonal signal, with implications for weight management, appetite-focused dietary strategies, and the inflammatory environment of skin.

Ghrelin was discovered in 1999 – relatively recently in endocrine terms – by Kojima and colleagues, who identified it as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). Its name derives from the Proto-Indo-European root “ghre,” meaning to grow, reflecting its original identification as a growth hormone releaser. The appetite-regulating role, now its best-known function, emerged from subsequent research and has since dominated the clinical conversation about ghrelin. But reducing ghrelin to a simple hunger signal understates both its complexity and its relevance to weight management strategy.

What Ghrelin Is and Where It Comes From

Ghrelin is produced predominantly by X/A-like enteroendocrine cells in the oxyntic glands of the stomach fundus – the upper portion of the stomach, furthest from the pyloric outlet. Smaller amounts are produced in the duodenum, with minor contributions from the hypothalamus, pituitary, and other tissues. The stomach is the primary source: circulating ghrelin levels fall dramatically after total gastrectomy, confirming that gastric production accounts for the majority of the systemic signal. ^[2]

Before ghrelin can bind its receptor and stimulate appetite, it requires a post-translational modification that is unique in human endocrinology: the addition of an octanoyl (eight-carbon fatty acid) group to the serine residue at position three of the peptide. This acylation step is catalysed by ghrelin O-acyltransferase, commonly abbreviated GOAT – an enzyme embedded in the endoplasmic reticulum of ghrelin-producing cells. Without GOAT-mediated acylation, ghrelin circulates as des-acyl ghrelin: present in the blood at higher concentrations than acyl-ghrelin, but unable to bind GHS-R1a and therefore lacking the appetite-stimulating and growth hormone-releasing effects of the active form. ^[2]

This distinction between acyl-ghrelin (active) and des-acyl ghrelin (inactive for appetite) matters practically because GOAT’s activity is influenced by dietary fat – specifically medium-chain fatty acids, which can serve as substrates for the acylation reaction. This provides a mechanistic basis for observations that dietary fat composition may influence ghrelin’s orexigenic activity beyond simple caloric considerations, though the full clinical implications of this pathway are still being investigated. ^[3]

How Ghrelin Works: The Hunger Signal

Acyl-ghrelin binds the GHS-R1a receptor, a G-protein-coupled receptor expressed most densely in the hypothalamic arcuate nucleus – the same region where GLP-1 and leptin exert their appetite-suppressing effects. The competing nature of these signals is deliberate architecture: the arcuate nucleus integrates hunger-promoting inputs (ghrelin, NPY/ AgRP neurons) and satiety-promoting inputs (GLP-1, leptin, POMC neurons) to generate a net appetite output. When ghrelin binds GHS-R1a, it activates NPY and AgRP neurons, which then suppress POMC activity and increase appetite – effectively flipping the arcuate nucleus into hunger mode. ^[3]

Beyond the hypothalamus, GHS-R1a is expressed in the brainstem, pituitary, and in the mesolimbic dopamine system, including the ventral tegmental area and nucleus accumbens. This mesolimbic expression is what connects ghrelin to hedonic eating – eating driven by reward and pleasure rather than energy need. Ghrelin signalling in the reward circuitry increases motivation to seek food, amplifies the rewarding value of palatable foods, and contributes to the food preoccupation that accompanies caloric restriction. This is a meaningful distinction: ghrelin doesn’t simply make you hungry, it makes food more rewarding – which is why elevated ghrelin can drive disproportionate cravings for highly palatable, energy-dense foods that go beyond what homeostatic hunger alone would explain. ^[1]

The Ghrelin Rhythm: Anticipatory, Meal-Matched, Restriction-Sensitive

Ghrelin levels are not static. They follow a characteristic diurnal pattern: rising in the hours before expected meals, peaking just before eating, and falling sharply within 30–60 minutes after a meal. This pre-meal rise is partly anticipatory, governed by meal timing – the body learns when food typically arrives and begins preparing the appetite system in advance. This is why skipping a habitual meal produces a particularly strong hunger signal, and why irregular eating patterns can generate ghrelin spikes at unpredictable times.

What is most clinically relevant for weight management is ghrelin’s response to negative energy balance. Caloric restriction reliably increases circulating ghrelin, and weight loss – whether through dietary restriction, GLP-1 RA medication, or both – is accompanied by a sustained rise in ghrelin levels that persists well beyond the period of active restriction. Research in diet-induced obese mice demonstrates that calorie-restricted weight loss not only raises circulating ghrelin but restores ghrelin sensitivity in arcuate NPY/AgRP neurons – which had become partially resistant to ghrelin signalling during obesity – meaning the same ghrelin signal produces a stronger appetite response after weight loss than it did before. This ghrelin sensitivity restoration is a key mechanism underlying the post-weight-loss hunger surge that drives weight regain, and it is the physiological basis for the ghrelin rebound phenomenon discussed in the Ghrelin Rebound entity. academic.oup

The Ghrelin–GLP-1 Counter-Signal Relationship

Ghrelin and GLP-1 function as reciprocal regulators of appetite at the level of the arcuate nucleus. GLP-1 activates POMC neurons and suppresses NPY/AgRP activity; ghrelin does the opposite. In healthy weight homeostasis, these signals fluctuate in a coordinated pattern around meals: GLP-1 rises as nutrients reach the ileum, generating satiation; ghrelin falls as the meal is consumed, removing the hunger drive. Between meals, as GLP-1 returns to baseline, ghrelin rises again in preparation for the next meal.

GLP-1 RA medications suppress this counter-signal by maintaining elevated GLP-1R activation continuously. Whilst on medication, ghrelin’s pre-meal rise is blunted and its orexigenic effect is overridden by the pharmacological satiety signal. When GLP-1 RA medication is discontinued, this pharmacological suppression is removed – and ghrelin, sensitised by any weight that has been lost, reasserts itself at elevated levels. This is developed in detail in the GLP-1 Medication Discontinuation entity.

Ghrelin and the Skin: An Emerging Connection

Ghrelin’s relevance to an aesthetics context is not immediately obvious, but the evidence for skin-related effects is genuine and mechanistically grounded.

Ghrelin receptors (GHS-R1a) are expressed in keratinocytes, and research demonstrates that ghrelin exerts anti-inflammatory activity in skin through suppression of NF-κB-mediated cytokine production. In inflamed keratinocyte models, ghrelin reduces TSLP (thymic stromal lymphopoietin), IL-4, IL-13, IL-22, and IL-31 expression – cytokines central to the type 2 inflammatory pathway that drives atopic dermatitis and suppresses filaggrin production. The mechanism involves glucocorticoid receptor activation and PKCδ-mediated phosphorylation of p300, reducing NF-κB p65 binding to inflammatory gene promoters. ^[4]

This positions ghrelin as a hormone with peripheral anti-inflammatory effects in skin that run counter to its central appetite-stimulating role. The practical implication is nuanced: chronically elevated ghrelin during restriction or post-medication weight regain is primarily a metabolic and appetite problem, but its skin effects appear to be anti-inflammatory rather than harmful. What does damage skin is the cortisol elevation that accompanies the same restriction states that drive ghrelin up – the two hormones frequently rise together under caloric deficit, but their skin consequences are opposite.

Clinical Pearl In clients presenting with reactive or atopic-tendency skin alongside a history of caloric restriction or weight loss medication, the ghrelin elevation itself is unlikely to be driving the skin inflammation. The more clinically relevant driver in that context is the cortisol rise that accompanies restriction, which suppresses filaggrin expression, impairs ceramide synthesis, and degrades collagen – the established restriction–skin cascade detailed in the Cortisol and Skin Barrier entities.