For starters, ketogenic dieting is based upon the removal of nearly all carbohydrates from one's diet for a certain period of time. In the absence of carbohydrates, the body will resort to stored fat (triglycerides) as its primary fuel source. Stored fat is broken down into ketones which the body then uses for energy. In order to enter this state of ketosis, one's liver glycogen must be emptied. Ingested carbohydrates are stored in the liver as glycogen, as well as in the muscles. When the liver is depleted of glycogen, a state of ketosis is achieved. Ketones are a by-product of fat (Triglyceride) burning, therefore while in a state of ketosis, the body is burning stored fat as its main source of fuel. The object of a ketogenic diet is to deplete the liver of its glycogen stores as quickly as possible so that fat burning occurs. This is done by severely restricting carbohydrates and eating only sources of High Level proteins.
Many people have brought up the issue that a low carbohydrate diet will cause lethargy and weakness. This is a common side effect during the first 48 hours until they reach a state of ketosis, as your body is using its remainder of "easy energy" storage, so you feel tired and hungry. Just like with anything else, there is a period of adaptation. This is not a low carbohydrate diet. It is essentially a NO carbohydrate diet. While on a LOW carbohydrate diet, enough carbs are always eaten to avoid entering into a state of ketosis but not enough carbs or total calories to maintain adequate energy levels. Dropping the carbohydrate count further and raising the protein levels will allow the body to enter ketosis and use ketones, or stored fat as fuel. While in a state of ketosis, one feels energetic and does not experience the general lethargy found with basic LOW carbohydrate diets. Ketones also enable one to maintain regulated insulin levels throughout the day which again will cause one to feel energetic. Below we can see the difference between a basic low carb diet and the Ketogenic Diet.
Basic Low Carb Diet: