Blood

Blood is an essential fluid of many life forms, Gallifreyans and Humans included.

Some species, such as Vampires and Haemovores (DW: The Curse of Fenric) consumed blood in order to survive.

On their home planet, the Ogri subsisted on amino acids, but found that the blood of Earth life forms, including Humans, would do just as well. (DW: The Stones of Blood)

Other species, such as Vortisaurs (BFA: Storm Warning) and Androgums (DW: The Two Doctors) do not subsist off of blood exclusively but will consume it as part of a more varied diet.

The Sycorax and other species used a form of biotechnology known as blood control.