Food is the body’s fuel. Now a study finds that the amount of energy in that fuel can depend not just on its calorie content—but on how it’s prepared. And the research, published in the Proceedings of the National Academy of Sciences, could explain an ancient leap in human evolution. Food’s energy value is usually measured before consumption. But Harvard scientists fed two groups of mice either meat or sweet potatoes and prepared the items differently: either whole or pounded, raw or cooked—to create a variety of diets. The researchers then measured the mice. They found that pounded meat and potatoes caused more weight gain than raw food. And that cooking increased weight the most. The extra calories cooking makes available may have allowed the survival of humans with larger bodies and more complex brains, starting almost two million years ago. Those physical changes required more energy, and exposing food to fire may have provided that boost. Of course, a legacy of evolution is that modern humans often gain too much weight. Which might be called a raw deal.