It’s to do with the hunger hormone ghrelin, according to a mouse study. 

Getting a bit hungry by fasting and cutting out snacks could actually make you want to exercise – not veg out on the couch as you might think.

And that sudden burst of energy may come from a surprising property of the “hunger hormone” ghrelin, according to new research led by Yuji Tajiri at the Kurume University School of Medicine in Kurume, Japan.

In an era where heeding the call of the stomach just means schlepping from the sofa to the fridge, it might not be obvious why hunger should prompt exercise.

But Tajiri and colleagues remind us that many animals only get a feed if they forage or hunt, so it makes sense that hunger would make them want to move. In fact, studies in mice show that when food is cut back they exercise more.

As for what might be causing that behaviour, the researchers had ghrelin sized up as chief suspect.

The hormone’s main claim to fame is that it makes you hungry. When energy stores dwindle, it is made in the stomach and talks to the brain to get you eating. But ghrelin is working more than one job. Mouse studies show it also helps endurance exercise by turning on adrenalin and the body’s glucose-making machinery.

So, ghrelin looks like it can sustain exercise. But Tajiri’s team wanted to know if it could actually motivate exercise in the first place, and set up some meticulous experiments in mice to investigate.

Read the full story in Cosmos magazine here