As the name suggests, it has a slightly sweet, buttery flavor. And if you’re looking for a slimming side dish, butter lettuce (sometimes called Boston Bibb lettuce) can’t be beat. According to USDA researchers, you’d have to eat six cups of the stuff (packed!) to match the calories in a single slice of bread. To make sure you get the tastiest possible head, scratch and sniff the stalk -- the sweeter the smell, the sweeter the flavor.