The short answer: Not really! Though they do contain 45 grams of fat in a 100-gram serving, nearly 90 percent of the fat is mono- and polyunsaturated fats. “I think many people are still on the fat phobic train in which they associate any type of dietary fact with a fear of ‘getting fat,’" Liz Shaw, a registered dietitian who consults Wonderful Pistachios, told RealSimple.com in an e-mail. “I’m constantly helping clients move past the total fat numbers and instead focus on fueling their bodies with unsaturated, heart-healthy fats.” Pistachios are actually known as “the skinny nut,” since they have the lowest amount of calories per single ounce serving of any tree nut. You can eat 49 nuts as a healthy snack—the standard serving size—and at three calories a nut, still only consume 147 calories.