Gluconeogenesis is a big word, but it's important because it's why low carbing works. Let's break it down:
gluco - glucose (a carbohydrate)
neo - new
genesis - to make
Gluconeogenesis means "to make new glucose." It's a process that happens in the liver. The liver uses a set of enzymes to take the glycerol backbone of lipids or amino acids (the building blocks of protein) and convert them to glucose. People will often tell you that you need to eat carbohydrates to be healthy. You don't. In fact, if you ate nothing but protein, your body would be able to make about 400 grams of carbohydrate every day from the amino acids in that protein. (Not recommended, of course, but it's theoretically possible.) More tomorrow.
(The picture is from the Elmhurst College Virtual Chembook by Charles E. Ophardt.)