Unless you’re a fan of steak tartar, cooking meat before you eat it is a matter of course. It’s a culinary custom that human ancestors may have been practicing for millions of years. But is there a reason behind why we’ve been doing it all this time? It could be that prepared animal proteins can provide a body with a “pick-me-up.” In a first-of-its-kind study, Harvard researchers investigated the energy a body gains from consuming cooked meat.

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In the study, two groups of mice were given a series of diets of sweet potatoes or beef, served either raw and whole, raw and mashed, cooked and whole, or cooked and mashed. While activity levels—measured by time spent on an exercise wheel—didn’t vary across the different diets, the mice required less cooked food to maintain those activity levels and those on cooked food diets maintained a higher body mass. Mice also exhibited a preference for cooked foods, suggesting that the test subjects themselves were noting a benefit from this particular diet.

Meat and tubers have been food sources for humans for at least 2.5 million years, although without the ability to control fire, food processing consisted of mashing or pounding at the most. But about 1.9 million years ago, human bodies began developing physical traits for long-distance running, and brain and overall body size grew larger—all of which are adaptations that require more energy to support. While earlier theories suggest that the incorporation of meat into the diet was responsible for these changes, this study suggests that cooking the meat allowed our ancestors to gain more energy from their foods, facilitating biological changes. In modern humans, the study notes, raw foodists can experience chronic energy deficiency as well as issues with fertility, and the authors suggests that cooking is necessary for normal biological functions.