Eating from nose to tail means getting lots more fat than you would if you only ate the muscle, because bones and organs have a lot of fat. Or so I read in many paleo articles/threads. Bone marrow is essentially all fat. But organs?
Am I missing something? The fat content of organs looks to be almost exactly the same as meat we usually eat, or less if your meat is grain-fed. As a disclaimer, I know nothing about offal, so there may be a big hole in this reasoning.
The things that come to mind that were eaten by our paleo friends that are high in fat are brains and sweet breads.
Cow brains are like 48 grams of fat per pound, I am going to guess that this is similar for many other animals.
Sweetbreads are 28 grams of fat for 4 oz. They are something like 70% fat.
Even a 1:1 ratio of fat to protein is still a pretty fatty slice of meat.
From what I've seen, most organs are generally understood to be high protein, not high fat, and are more often touted for providing nutrients that may be lacking in muscle meat. Vitamin A in liver, for example. The degree to which the organs are cooked influences the vitamin content, of course.
Here's a good breakdown of the nutrients in calf's liver: http://www.whfoods.com/genpage.php?tname=foodspice&dbid=129
(The link does happen to say that it's high in saturated fat as well as protein - but that's from a Whole Foods fat-phobic standpoint.)