A “ketogenic” diet is low in carbohydrates, high in fats and moderate in protein. When you consume carbohydrates (or excess protein), the body breaks it down into an easy-to-use sugar called glucose. It will also produce insulin, which “signals” the presence of glucose in your bloodstream  – and when our insulin production becomes “fatigued”/maladapted (from too much glucose too often) we call it diabetes. From keto-fied:

There are two main things that happen to glucose if your body doesn’t need it:
  • Glycogenesis. Excess glucose will be converted to glycogen, and stored in your liver and muscles. Estimates show that only about half of your daily energy can be stored as glycogen.
  • Lipogenesis. If there’s already enough glycogen in your muscles and liver, any extra glucose will be converted into fats and stored.
However, on a low-carb diet (less than 50g; even < 20g), there is no glucose available and another system must be relied upon:
When fat is broken down by the liver, glycerol and fatty acid molecules are released. The fatty acid is broken down further, in a process called ketogenesis, and a ketone body called acetoacetate is produced. Acetoacetate is then converted into 2 other types of ketone bodies:
  • Beta-hydroxybutyrate (BHB) – After being keto-adapted for a while, your muscles will convert the acetoacetate into BHB as it’s preferred by the brain for fuel (i.e. converted to ATP by the mitochondria inside our cells).
  • Acetone – Can sometimes be metabolized into glucose, but is mostly excreted as waste. This gives the distinct smelly breath that most ketogenic dieters know.
Over time, your body will expel fewer ketone bodies, and you may think that ketosis is slowing down. That’s not the case, as your brain is burning the BHB as fuel, and your body is trying to give your brain as much efficient energy as possible.