A group of brain cells in mice seems to trigger hunger based on what time of day the animals usually eat 鈥� and the neurons鈥� activity can be reset by forcing a change in feeding patterns.
If the results translate to people, it could explain why we tend to feel hungry around our usual breakfast, lunch or dinner times, even if a previous meal was super-sized. 鈥淲e used to think that hunger slowly creeps in as energy resources diminish over time,鈥� says at the University of Iowa. 鈥淚nstead, ups and downs in neuron activity appear to follow the recent feeding pattern. It鈥檚 like these neurons yell 鈥榙inner time!鈥欌��
The body has multiple mechanisms that regulate hunger. A major one is a group of brain cells called AgRP neurons, at the base of the brain, which seem to trigger hunger by raising their firing rate. Weight-loss injections such as semaglutide, sold as Wegovy, partly work by suppressing the activity of these brain cells.
Advertisement
It was generally thought that the neurons鈥� activity is governed by levels of nutrients, for instance blood sugar levels, which fall in the hours after eating. But the new study, the first to measure the activity of these neurons over several days, shows that, in mice, they are controlled by the animals鈥� usual eating patterns.
In the first part of the experiment, the mice were allowed to eat whenever they liked, which was at nighttime as the animals are nocturnal. The team was surprised to see the neurons鈥� activity didn鈥檛 rise gradually over the day, as would be expected if they were triggered by falling blood sugar levels, but rose suddenly when the animals woke up.
The neurons鈥� activity also dropped sharply at the end of the night, even if no food was provided all night. 鈥淚t鈥檚 almost like there鈥檚 a clock telling the neurons that it鈥檚 time to eat, it鈥檚 time to stop eating,鈥� says Atasoy.
Next, the researchers provided food for the mice only for a short window in daylight, between 10am and 2pm, forcing the rodents to be awake then in order to eat. After seven to 10 days, their brain cells gradually switched to becoming more active shortly after 10am. 鈥淭his circuit enables mice to feel hungry at the times of day they are used to eating,鈥� says Atasoy.
If the results translate to people, it suggests that these cells help us to get used to different eating patterns, for instance if someone works night shifts or adopts a fasting diet, where food intake often only happens within an 8-hour window, says Atasoy.
鈥淚t鈥檚 reasonable to hypothesise that the systems are similar in people鈥�, seeing as humans also have AgRP neurons, says at the University of Washington in Seattle. The results may explain why people generally don鈥檛 feel hungry in the middle of the night, while skipping an expected meal in the daytime usually does trigger hunger, he says.
Nature Neuroscience
Article amended on 22 November 2023
The headline of this article has been changed to better reflect the findings of the research.
