I won’t lie―bones, connective tissues and organ meats excite me. When I open up the freezer at Cricket Creek Farm and slide out those plastic bins to find hearts, livers and marrow bones, I feel like a little kid in a candy store. Now, some of these parts are fairly straightforward to prepare―heart is similar to a lean steak (it is a muscle, after all) and does well when pan-seared―while others, such as kidneys, still present me with a culinary challenge (they’re just naturally pretty funky). But why all the excitement? The answer is that organ meats are among the most nutrient-dense foods available to us. They also may help to alleviate imbalances among nutrients, some of which are found in more common foodstuffs. One example of such an imbalance occurs when our intake of methionine ― an essential amino acid abundant in lean muscle meats and eggs―outstrips our intake of the nutrients necessary to direct the proper usage of methionine and to help detoxify our bodies of homocysteine ―a byproduct of methionine metabolism which may contribute to degenerative illnesses such as atherosclerosis.  
Methionine plays important physiological roles, two among which are methylation and the production of the endogenous antioxidant and detoxifier glutathione. The first role takes physiological precedence, which is to say that the pathway through which methionine is used to produce glutathione becomes activated only once our intake of methionine surpasses the threshold required by our bodies for sufficient methylation. But here’s the (first) rub: homocysteine is generated as a byproduct of methylation, and our bodies require folate and vitamin B12 in order to recycle homocysteine back into methionine. So a deficiency in folate and vitamin B12 can result in an excess of homocysteine. And here’s the second rub: the liver requires vitamin B6, glycine, choline and betaine in order to successfully convert excess methionine―resulting from the consumption of significant quantities of muscle meats and eggs―to glutathione. A deficiency in these nutrients can lead in turn to excess methylation and hence excess accumulation of homocysteine. 
The takeaway is that we must attempt to achieve a balance in our diets―in this case, a balance between our intake of methionine and our intake of the essential B-vitamins, glycine, choline and betaine. Muscle meats provide some vitamin B6, and egg yolks are a good source of choline. (Our bodies can produce betaine from choline, or we can get betaine from spinach, wheat and beets.) But all of the B-vitamins required for homocysteine recycling can be found abundantly in liver (as well as can choline)! Furthermore, muscle meats are a poor source of glycine, which is instead found in greater abundance in bone, skin, connective tissue and broths made from these parts. What fascinates me is that the balance in nutrients that we require is reflected in a balanced consumption of different parts of the animal―its bones, skin, organs and connective tissues as well as its muscle meats. And this makes sense at a heuristic level. Meat is nutritious because animal physiologies require and therefore accumulate almost all of the same nutrients that human physiologies require. But our physiology does not consist entirely of muscle, and so we wouldn’t expect to derive all of the nutrients we require from muscle alone. We are a balanced, organized system of diverse tissues and organs, and it makes sense that to support such a system the meat products we consume must reflect that diversity. So I encourage you on your next rummaging through the freezer at the farm store to expand your horizons if you haven’t already and try some liver!
-Christ Masterjohn explains the physiological processes summarized above in much greater detail here. Fascinating, as usual!
-My go-to recipe for beef liver pate!