Pistachios in the shell may not be as popular as traditional choices like carrots for a healthy (practically no-cal) snack, but as one of the lowest calorie nuts, they have another advantage: shelling them slows down snacking - and a growing pile of shells shows may remind you of how much you've eaten. A study from Eastern Illinois University found that students given unshelled pistachios ate 41 percent fewer nuts (an average of 125 calories per sitting) than those were given shelled nuts (they averaged 211 calories per sitting). The researchers also learned that when given a bowl of pistachios and a bowl for the shells for the day, the students ate 22 percent less when the shells accumulated all day than when the bowls were emptied every two hours. This study supports results from earlier investigations suggesting that pistachios can be a healthy "diet" food: UCLA researchers found that snacking on pistachios was better weight-wise than snacking on pretzels. And a U.S. Department of Agriculture study found the body may not completely absorb the fat in pistachios, which would make the nuts even lower in calories than we think.