I think you might be getting your wires crossed.
He's asking where they get the dietary components that we get from fruit and veg.
These components cascade down the food chain and many are stored by other animals, which we could eat if we did not have more efficient alternatives at hand (IE fruit and veg).
Inuit and Eskimo do not have easy access to fruit and veg, so they need to eat animals that do in order to get the same components. Vitamin D will be another one, as well as calcium and trace metals.