For most of human evolutionary history, calories were scarce and uncertain. So even today, we want to store as much energy as possible. That mindset hinders appetite in several ways. Our instincts tell us to keep eating well beyond when we are sated. Worse, the foods we crave—calorie-dense fats and sugars—were once rare and valued as a bulwark against starvation; now they're plentiful and harmful in excess. And we don't crave plants, precisely because they were more abundant in our past.