Many times when we see low-fat on a label we are led to believe the product to be healthy. Ruth Frechman, RD for the Academy of Nutrition and Dietetics, says that with peanut butter about one-fourth the healthy fat is removed for the low-fat version. To compensate for a better taste, often sugar and salt are added. The lesson to take away is to always check the label and read the list of ingredients. In the case of peanut butter, buy the natural. When you read the ingredients you will see only one, peanuts.
Source: ACE Get Fit Ask The Expert Blog