No matter how much fun you have into the wee hours of the morning, hangovers are a rough trade-off for a night of boozing. Friends may suggest and swear by dozens of so-called cures, from a very specific type of ice cream, to listening to music, to the “hair of the dog” method. But sometimes all you want is a few gallons of water and a big plate of the greasiest food you can find. So what is it about greasy food that is so enticing when you’re trying to remember what you did with the Advil, but your head hurts too much to think about it? The answer may have something to do with laziness and your need to re-energize.

“One of the most powerful laws in psychology is the law of least effort,” Cornell University College of Human Ecology professor David Levitsky tells mental_floss. “Greasy food is a surrogate for fat and fat is the nutrient for the highest energy density. We go for calorically dense food because it takes the minimum of preparation and yields [the] highest caloric payoff.”

As someone whose job is to teach others about nutrition, Levitsky acknowledges that this craving is not the smartest idea, but sometimes the hunt for energy becomes a higher priority than maintaining a healthy diet. “Evolution doesn’t care that it will kill you when you are 70,” he says. “You have finished procreating by then.” 

If you’d rather not accept the idea that you were temporarily not strong enough to resist temptation, there is another theory that may shift the blame to your brain. International Business Times cites a 2004 study by Princeton University that suggests that a chemical in the brain called galanin is the real culprit. The study involved injecting rats with the chemical to see how it affected their consumption of alcohol. Rats injected with galanin were found to consume more alcohol, even when their food and water intake remained normal. When observed during the day, the otherwise nocturnal rats would drink alcohol during hours that did not match their usual eating and drinking schedules, but they would still not drink water off-schedule and would not eat.

“There seems to be a cycle of positive feedback,” Bartley Hoebel, the study's co-author, said. “Consumption of alcohol produces galanin, and galanin promotes the consumption of alcohol. That would perpetuate the behavior.”

"Alcohol is the only drug of abuse that is also a calorie-rich food, and it undoubtedly has important interactions with systems that control food intake and nutrition," researcher Michael Lewis added.

So the next time you party hard all night, roll out of bed the next afternoon, and head to the nearest diner or fast food restaurant, there are two possible explanations to choose from while fighting off those judgmental stares.

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