Researchers started noticing ghrelin's effects on brain power as far back as 2006, when a study published in Nature Neuroscience showed that mice injected with extra ghrelin improved their performance on memory and learning tests by as much as 40 percent. But perhaps more importantly than boosting normal brain power, other research has found that it could actually keep brain cells from dying.

Dr. Jeffrey Davies of Swansea University in the U.K. has spent the better part of a decade studying this multipurpose hormone. A 2017 study he published in the Journal of Neuroscience found that ghrelin helped keep brain cells healthy in mice with Parkinson's Disease, and another study he published in the Journal of Neuroendocrinology in the same year found that ghrelin injections improved memory and spatial orientation in mice with Alzheimer's disease.

This might sound counterintuitive. Why would a hormone that makes you hungry also improve your brain function? But it makes sense from an evolutionary standpoint. If you're a hungry animal in the wild, you need to be mentally sharp to find that next meal. Your life — and offspring — depend on it.

If your brain benefits from ghrelin and ghrelin spikes when you're hungry, does that mean that you should skip breakfast before a big exam? Fortunately, no. For one thing, a 2005 review of 47 studies found that eating breakfast is associated with improved cognitive function. Don't mess with that! But more importantly, ghrelin's effects on brain cells don't happen in the short term, Nicolas Kunath of the Technical University of Munich tells New Scientist. New brain cells can take weeks to start working. But there are some people who advocate for permanent calorie restriction—around 500 to 800 calories below what's usually recommended—for the health and cognitive benefits. It's not easy (and should definitely not be attempted by those with a history of disordered eating) but a vocal minority swear by it.

Want a way to sharpen your mind without, you know, starving? Check out "Brain Food: The Surprising Science of Eating for Cognitive Power" by neuroscientist and certified integrative nutritionist Lisa Mosconi, Ph.D. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.