Have you ever tried to go to sleep hungry? Believe me, it doesn’t work. You just end up lying in bed, listening to your stomach growl, and dreaming about your favorite foods. Have you ever experienced a “food coma?” Think back to last Thanksgiving when you ate so much that all you wanted to do afterwards was take a long nap. Clearly, hunger and sleep are closely related. But how?
Studies in humans suggest that sleep deprivation is linked to having higher levels of ghrelin, aka the “hunger hormone,” which make you feel hungrier even after a single sleepless night. More evidence from people with sleep disorders like insomnia reveals that sleep disturbances cause people to binge eat even late at night. But why?
One molecule, called Neuropeptide Y (NPY), has been shown to play a critical role in regulating eating and metabolism in rats and humans, but it is unclear how it affects sleep. Depending on the level of wakefulness of the subject, the addition of NPY can either promote or suppress sleep. To clarify this conundrum, a research team led by Leslie Griffith at Brandeis University studied the role of an NPY-like protein sNPF in regulating and promoting sleep in fruit flies.
In this study, published in last month’s issue of The functional unit of the nervous system, a nerve cell that..., a heat-activated cation channel was selective expressed in sNPF neurons, causing those specific neurons to be activated when the fruit flies were put in a warm environment. When sNPF neurons were activated, the fruit flies fell asleep almost immediately, as shown by the lack of movement by the flies in the right vial in the video below. Amusingly, the flies were so sleepy that they would only wake up to eat a bit before nodding off again – right on top of their food! Importantly, when the sNPF neurons were allowed to function normally again, the fruit fly activity returned to normal, and they slept even less when they were supposed to be sleeping, suggesting that their couch potato-like behavior really was sleep.
So, what do fruit fly sleep patterns have to do with obesity? Well, in humans NPY has been studied as a possible drug target for obesity treatment, even though scientists don’t fully understand how its regulation affects sleeping and eating. Studies like this one in fruit flies help elucidate which cells, proteins, and genes are involved in turning on and off these behaviors, provide important clues about the relationship between hunger and sleep, and hopefully lead to a better understanding of human health.
Eiber R and Friedman S. An association between two quantities such that one varies w... between eating disorders and sleep disturbances. Encephale. 2001; 27:429-34. PMID: 11760692
Schmid SM, Hallschmid M, Jauchchara K, Born J, Schultes B. (2008). A single night of sleep deprivation increases ghrelin levels and feelings of hunger in normal-weight healthy men, Journal of Sleep Research, 17 (3) 331-334. DOI: 10.1111/j.1365-2869.2008.00662.x
Shang Y., Donelson N., Vecsey C., Guo F., Rosbash M. & Griffith L. (2013). Short Neuropeptide F Is a Sleep-Promoting Inhibitory Modulator, Neuron, 80 (1) 171-183. DOI: 10.1016/j.neuron.2013.07.029
Taheri S., Lin L., Austin D., Young T. & Mignot E. (2004). Short Sleep Duration Is Associated with Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index, PLoS Medicine, 1 (3) e62. DOI:10.1371/journal.pmed.0010062
Images adapted from gymflow100.