Hunger Hormone 'Ghrelin' Boosted By Restricted Meal Times

The "hunger hormone" ghrelin helps rats with restricted feeding schedules learn to eat more, according to a recent study.

Researchers at the University of Southern California found that once rats knew about their limited eating schedule, they started doubling their food intake.

"We are looking deep into the higher order functions of the brain to unpick not just which hormones are important for controlling our impulses but exactly how the signals and connections work," said lead author Scott Kanoski from the USC Dornsife College of Letters, Arts and Sciences, in a news release. 

During the study, meals for the rats were restricted to a daily four-hour window, followed by 20 hours with no food. Yet researchers found that the hormone ghrelin helped rats reduce their feeling of fullness so that they were gradually able to eat more.

The way ghrelin works is that the hormone communicates with neurons from the hippocampus to stimulate appetite--allowing for a large amount of food to be eaten in a very limited amount of time. The neurons then communicate with another part of the brain known as the hypothalamus in order to produce the molecule orexin, which further promotes hyperphagia, or excessive eating.

Previous research has shown how ghrelin signals the hippocampus to increase rats' food intake when the creatures see a visual signal that they have learned to associate with an imminent meal. Researchers noted that the human equivalent of this might be a fast-food billboard that makes individuals think of food quickly and that is difficult to resist wanting to purchase and consume something to eat. Furthermore, ghrelin has also been found to increase the rate at which nutrients pass through the body--something that is best to happen slowly in order to create a feeling of fullness over longer periods of time.

Right now, researchers are working to reduce ghrelin's effect by genetically suppressing the activity of the its receptor in the hippocampus by disrupting neurochemical signals that facilitate the consumption of large quantities of food.

The study is published in the journal eLife.

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