Any answer that a nutritionist would give you be couched in a whole list of qualifiers (if you have low cholesterol, if you're over the age of 65, etc) since you're asking questions about the interactions between very complicated systems like any good scientist should. If someone did give a binary answer to any of the questions you asked, they're probably wrong or trying to sell you something. Don't interpret that as lack of understanding, there is quite a bit known about human nutrition in the modern era.