Pistachios do contain fat, but they aren't necessarily fattening. These flavorful nuts also contain other important nutrients, including protein, potassium and heart-healthy unsaturated fats. Calories are a consideration during weight-loss plans; by choosing in-shell pistachios over the preshelled version, you may find yourself eating fewer calories.
Pistachios offer 4 calories per nut. One ounce -- about 49 nuts -- has 159 calories, 5.75 grams of protein, 7.8 grams of carbohydrates and 12.87 grams of fat. Although 1.575 grams of this fat are saturated, the rest is in the form of monounsatured and polyunsaturated fats. Harvard's School of Public Health considers these "good" fats, as they protect the heart and many other parts of the body.
"Fattening" Is About Calories
According to Harvard's School of Public Health, what really matters regarding weight loss is the number of calories consumed. The school highlights one study -- the 2006 Women’s Health Initiative Dietary Modification Trial -- indicating that people who ate nuts gained less weight during the course of the study than those who didn't eat nuts. The study also showed that women consuming a low-fat diet did not lose or gain more weight than people on any other kind of diet.
A Chinese study published in the January 2012 issue of "Nutrition Journal" also showed that eating pistachios doesn't have to equate to weight gain. Over the course of 12 weeks, the study's subjects ate about 1.5 or 2.5 ounces of pistachios daily. In both cases, the participants did not gain weight or experience an increase in waist-to-hip ratio. The study focused mostly on metabolic syndrome, but it also applies to those simply looking to shed a few pounds.
A 2011 Eastern Illinois University study found that choosing shell-in pistachios over shelled may result in lower calorie intake. Students were given either shell-in or preshelled nuts during a class period, after which their caloric intake was measured. Students with the shell-in pistachios ate about 125 calories, while those eating preshelled pistachios ate about 211 calories. The study also noted that students' sense of fullness and satisfaction was about the same regardless of their calorie consumption.