Liquid nitrogen should in no way be part of any liquid diet! Just touching it without protective gloves or clothing will cause a severe case of frostbite. Swallowing it is unthinkable, though some people do use it to make ice cream and other frozen desserts.
Liquid nitrogen isn’t poisonous. It’s odorless, colorless and nonflammable, somewhat water-soluble and basically inert. Yet it’s quite hazardous to handle. It carries a risk of explosion in a sealed container, and as it replaces any oxygen in the air, a person who’s handling it runs a risk of being asphyxiated if the area isn’t well ventilated.
However, liquid nitrogen has many beneficial uses. When a person orders a frozen food item, it’s likely that the item will be packed with liquid nitrogen to keep it frozen during shipping. It’s also used to freeze and preserve tissue samples, blood, reproductive cells and embryos and acts as a coolant for vacuum pumps and superconductors. It freezes the water in pipes so that the pipes or their plumbing system can be worked on. It’s also used to preserve the bodies of humans and animals till medical technology advances to the point where it’s hoped that they can be revived.
Dermatologists use swabs dipped in liquid nitrogen to destroy the cells of skin cancer and other abnormalities. Liquid nitrogen also protects materials from exposure to oxygen and cools them down so they can be handled with greater ease. It might be one of the liquids on airplanes, used to cool down parts of machinery or keep food frozen.
One of the weirder things it’s used for is promession. This is when a corpse is immersed in liquid nitrogen. This causes the body to be pulverized when the container is shaken a bit. The resulting powder is dried and used for compost.