Okay, there’s some science involved but I’ll answer your question at a basic level and then point you to additional resources if you’d like to dig deeper.
Ketosis is a metabolic state in which the body uses ketone bodies in the blood for some of its energy needs. This state is in contrast to glycolysis which occurs when blood glucose supplies the energy.
Ketone bodies are produced by the liver when there is the unavailability of blood glucose. This lack of blood glucose may be the result of fasting (restricting all nutrient consumption) or by following a ketogenic diet (restricting carbohydrate consumption).
Ketosis is considered to be present when ketone bodies blood levels are measured over a certain level – usually 0.5 millimolar.
The level of blood ketone bodies can be measured using three different methods:
- Blood test (considered most accurate)
- Breath test
- Urine test (considered least accurate)
Proponents of the keto diet believe that being in a state of ketosis causes fat deposits to be more readily released and consumed. This has led to ketosis being referred to as the body’s “fat burning mode.”
Again, there’s certainly more detail involved in understanding ketosis than what I just summarized. Here’s where you can learn more: