Unraveling the Mystery: Why Some Snakes Lack the 'Hunger Hormone' Ghrelin

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Unraveling the Mystery: Why Some Snakes Lack the 'Hunger Hormone' Ghrelin

In a fascinating twist to our understanding of animal physiology, recent research published in the February 1, 2026, issue of *Open Biology* has revealed that several snake species lack the gene encoding ghrelin, commonly dubbed the 'hunger hormone,' as well as the essential enzyme required for its activation. This striking discovery is prompting scientists worldwide to re-examine the intricate mechanisms governing appetite, metabolism, and survival in the animal kingdom, particularly given snakes' extraordinary capacity to endure weeks, or even months, without food.

Ghrelin has long been recognized for its role in stimulating hunger in mammals, with levels typically rising before meals to signal the body's need for sustenance. Its complete absence in a group of animals renowned for their fasting abilities presents a compelling paradox. This genetic anomaly suggests that the regulation of energy balance in these serpents might operate through entirely different pathways than those observed in most other vertebrates, challenging conventional physiological paradigms.

The discovery was serendipitous, emerging from a comparative genomic study led by evolutionary geneticist Rui Pinto and his colleagues at the Interdisciplinary Centre of Marine and Environmental Research in Porto, Portugal. While analyzing the genomes of 112 reptile species, including various snakes, crocodiles, and chameleons sourced from a public database, Pinto's team stumbled upon a consistent pattern: the ghrelin gene and its activating enzyme were conspicuously absent in 32 snake species. Intriguingly, this pattern was also observed in some chameleon species and toadhead agamas, lizards that, unlike snakes, tend to eat quite regularly. Conversely, crocodiles, which can famously go without food for over a year—even surpassing snakes in their fasting endurance—retain both ghrelin-related genes.

Pinto posits that the absence of ghrelin in snakes may have less to do with their appetite control and more with their unique metabolic adaptations. This hypothesis aligns with previous research on mice, where genetic deletion of ghrelin did not significantly alter food intake or body weight. Furthermore, in both mice and humans, active ghrelin levels, along with those of its activating enzyme, are known to *rise* after a meal, which seems counterintuitive if its primary function is solely to stimulate hunger. This suggests ghrelin's roles extend beyond mere appetite, possibly influencing fat storage regulation and insulin response.

Todd Castoe, an evolutionary geneticist at the University of Texas at Arlington, who was not involved in the study, described the findings as "striking" and acknowledged that many scientists, including himself, had overlooked this "really cool pattern." The genetic blueprint of snakes, particularly their metabolic pathways, appears to be profoundly divergent from that of mammals, potentially rendering ghrelin superfluous to their specific physiological needs.

However, other experts advocate for a cautious interpretation of ghrelin's metabolic significance. Tobias Wang, a zoophysiologist at Aarhus University in Denmark, points out that while ghrelin, like other hormones involved in appetite and satiety, certainly has metabolic effects, there is currently no robust evidence to suggest these effects are profound. Rute Fonseca, an evolutionary geneticist at the University of Copenhagen and a co-author of the study, also acknowledges that their current analyses are not exhaustive in fully elucidating ghrelin's myriad functions.

Further research is undeniably needed to fully comprehend ghrelin's complex roles and the precise implications of its absence in various animal species. Wang, for instance, expresses keen interest in experimental manipulations, such as deleting the ghrelin gene in crocodiles or administering the hormone to snakes, to observe the physiological outcomes. Castoe suggests that such comparative studies could yield invaluable insights into human metabolic disorders, including diabetes and obesity, opening new avenues for medical research. This discovery underscores the profound diversity of biological systems and the ongoing quest to unravel the evolutionary adaptations that enable life to thrive under myriad conditions.

Ekhbary News Agency