In this rat study, a hormone (ghrelin) that causes feelings of hunger when food is restricted and spurs the urge to eat, suppressed sleep:
Ghrelin-Induced Sleep Responses In Ad Libitum Fed And Food-Restricted Rats, Brain Research, May 2006
Sleep responses and motor activity after central administration of 0.2, 1, or 5 μg ghrelin in free-feeding rats as well as in feeding-restricted rats (1 μg dose) were determined.
Light onset injection of ghrelin suppressed non-rapid-eye-movement sleep (NREMS) and rapid-eye-movement sleep (REMS) for 2 h. In the first hour, ghrelin induced increases in behavioral activity including feeding, exploring, and grooming and stimulated food and water intake. Ghrelin administration at dark onset also elicited NREMS and REMS suppression in hours 1 and 2, but the effect was not as marked as that, which occurred in the light period. In hours 3–12, a secondary NREMS increase was observed after some doses of ghrelin. In the feeding-restricted rats, ghrelin suppressed non-rapid-eye-movement sleep (NREMS) in hours 1 and 2 and rapid-eye-movement sleep (REMS) in hours 3–12.
Data are consistent with the notion that ghrelin has a role in the integration of feeding, metabolism, and sleep regulation.
Hypothalamic Orexin Neurons Regulate Arousal According to Energy Balance in Mice, Neuron, June 200
(Orexic neurons are stimulated by ghrelin.)
Mammals respond to reduced food availability by becoming more wakeful.
The idea that ghrelin could disturb sleep was captured by mainstream media:
Trouble Sleeping? Some Bedtime Snacks Can Help You Sleep , WebMD, May 2008
Why Hunger Disrupts Our Sleep
This relatively new research focuses on leptin and ghrelin, two metabolic hormones that scientists discovered only during the last decade. When we eat, leptin signals that the body is satisfied, while ghrelin stimulates hunger. Researchers speculate that if we have enough leptin to suppress the secretion of ghrelin, we’ll sleep through the night without awakening to eat. “They act in see-saw fashion, counterbalancing each other,” says Culebras. “If the balance is thrown out of order, it may result in subtle signs that awaken us.”
Ghrelin is a fairly recent discovery. It does more than just induce hunger. Scientists are still learning.
Ghrelin, Molecular Metabolism, June 2015
The gastrointestinal peptide hormone ghrelin was discovered in 1999 as the endogenous ligand of the growth hormone secretagogue receptor. Increasing evidence supports more complicated and nuanced roles for the hormone, which go beyond the regulation of systemic energy metabolism. … In recent years, ghrelin has been found to have a plethora of central and peripheral actions in distinct areas including learning and memory, gut motility and gastric acid secretion, sleep/wake rhythm, reward seeking behavior, taste sensation and glucose metabolism.
Schematic on ghrelin’s physiological effects:
And this one for the graphic:
Hypothalamic Neurons That Regulate Feeding Can Influence Sleep/Wake States Based on Homeostatic Need, Current Biology, December 2019