Nuts vs Seeds

SA-RAW

Does anyone know why nuts are difficult to digest and seeds are easier? Is it safe to say that we can sub seeds for nuts in any recipe? What about dessert crusts, and ice cream? Do you use mostly pumpkin and sunflower? Last question... If the nuts have been completely blended or made into milk or flour is that safer? I personally don't care to eat nuts but some things just seem like you need them? What does everyone think about nuts vs seeds?