Peanuts are fattening in large quantities, since they are relatively high in calories. However, they are rich in unsaturated fat, protein and fiber, which means that, in small amounts, they can stave off hunger and stabilize blood sugar.
Peanut butter is also fattening, but can likewise be useful in small quantities for dieting. Peanuts and peanut butter have been shown not to cause weight gain when eaten as snacks every couple of hours.
Particularly when paired with dried fruit, celery, apple or banana or instead of butter or cheese on bread, peanut butter can be a very useful dieting aid. As a reference, 2 tablespoons contain 190 calories and 17 grams of fat.