When we eat, a series of chemical switches turns on, releasing bile, lowering blood sugar, and ramping up blood flow to the intestines. Fat stores are activated too, burning old calories to prep for the new ones in your meal. But now researchers have figured out how to hijack that process with a pill—no calories needed. Ronald Evans describes the finding this week in the journal Nature Medicine. So far, he and his colleagues have shown that the “imaginary meal” pill works in mice, helping them to shed extra weight. Can it do the same in humans?