Scientists in the US have found that walnuts have 21% fewer calories, while almonds have 20% less than what the label says, and pistachios have 5% less. This is because we don’t break the nut down fully before we swallow it. And this means we absorb fewer calories – and nutrients – than are available in whole nuts.  Researchers also advise eating a variety of types of nuts to reap all the nutritional benefits, which may be easier to do with whole nuts, which often come in bags of mixed nuts and have a longer shelf life than nut butters.
Source :  BBC