Fasting could boost your brainpower. A stomach hormone that stimulates appetite seems to promote the growth of new brain cells and protect them from the effects of ageing – and may explain why some people say that fasting makes them feel sharper. Ghrelin is known as the hunger hormone, as it is made by the stomach when it gets empty. If we go a few hours without food, its levels rise in our blood. But there is also evidence that ghrelin can enhance cognition. Animals fed reduced-calorie diets have better mental abilities. Injecting ghrelin into mice improves their performance in learning and memory tests, and seems to boost the number of connections in their brains. Now Jeffrey Davies at Swansea University, UK, and his team have found further evidence that ghrelin can stimulate brain cells to divide and multiply, a process called neurogenesis. When they added the hormone to mouse brain cells grown in a dish, it switched on a gene known to trigger neurogenesis. “If the same happens in animals, this could be how ghrelin affects memory,” says Davies, whose work was presented at the British Neuroscience Association conference in 2017. The work may have implications for treating neurodegenerative conditions. Davies's team have found that ghrelin, or chemicals that act the same way, could help treat some conditions like Parkinson’s disease.