Reindeer is known here in NA as caribou (same species for all intents and purposes). Like any mammal related to the Cervidae family, Reindeer is very lean and yes Hikermor is correct. A diet of this type of meat needs to be supplemented by other meat/fish to have a healthy intake of fat in order to survive long term where beef and other fattier meats are not available.
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.

John Lubbock