When body starts using fat as a primary fuel source, metabolism of fat produces ketones as a side product. This process of fat utilization and ketone production is called ketosis. If someone is on normal high carb diet then chances of body using fat as a primary energy source is very slim. Body use glucose as a primary energy source. However, ketosis can happen or can be induced. Depending on the level of ketone present in the blood, ketosis can be used to one’s advantage. This can also be fatal. Here are three types of ketosis that can happen in a human body
Nutritional ketosis
This ketosis can be induced by switching to high fat low carb diet. Since body does not have enough glycogen available it will start utilizing body fat as a fuel. This is the best ketosis and it have helped many people to loose weight. This have also helped many endurance athletes to improve their running or triathlon economy. According to a study there is range of ketone level that is optimized for weight lose or athletic activity. This is also called Optimizes Fat Metabolism (OFM). The concentration of ketones in blood while being on OFM ranges from 0.5-2.5 mM.
Starvation ketosis
As name suggests this ketosis happens when one stop eating. Since body will use all the available energy source stored in the form of glycogen and body will strat tapping on fat tissues present in the body. This kind of ketosis is not advised for longer period of time. The starvation ketosis will generate high concentration of ketones (more than 2.5 mM). This high concentration is not healthy
Diabetic ketoacidosis
As name suggest this type of ketosis happen when body stop producing insulin and blood glucose level is not controlled. Body will then produce very high amount of ketones that may be fatal.
Malik's Mobility-Ultrarunning, Ketogenic Diet and Fat Adaptation 