Fat and diet

The state of knowledge on the various types of fatty acids and health is a bit of a mess, even though some things appear to have been established.  Here is my understanding of the current knowledge/conventional wisdom. Saturated fat = good. Unsaturated fat = bad.  HDL cholesterol = good, LDL = bad. However, within unsaturated fat, there's still a lot of uncertainty.  Omega-3 = good because it's anti-inflammatory (I won't get into the pathway here because I don't yet fully understand it) and Omega 6 = bad because it's pro-inflammatory.  So the ratio of Omega-6/Omega-3 is important because if it gets too high then one is at risk for all kinds of inflammation throughout the body (and many disorders are inflammatory). There is a now pretty widely accepted hypothesis (I don't know if I would call it a theory) that the ancestral human diet was rich in omega-3 and that is what we are adapted to and the modern grain-based diet is more rich in omega-6 (from most vegetable oils).  Processed food is of course usually rich in omega-6 even if it is not rich (any more) in saturated fat.  Within omega-3, there are three main kinds: ALA from plant sources and DHA and EPA from animal sources (primarily fish oil and krill oil).  DHA and EPA can be immediately used by the human body (i.e. incorporated into cell membranes) wherease ALA needs to be processed by several enzymes into usable sources.  These enzyme reactions are slow and not very efficient.  So it is currently unclear whether ALA is as beneficial as DHA and EPA.  A lot of foods that have been enriched omega-3 (e.g. eggs, margarine) are enriched with ALA, not the other two.  ALA is probably better than either saturated fat or omega-6, but it's not clear how actually beneficial it is.  More science is needed...