Gluconeogenesis (GNG) is a metabolic process of making glucose, a necessary body fuel, from non-carbohydrate sources such as protein (amino acids), lactate from the muscles and the glycerol component of fatty acids.
Blood glucose levels must be maintained within a narrow range for good health. If blood sugar is too high, it results in tissue and organ damage. If it is too low, cellular respiration and energy production can suffer, especially if the body is "carbohydrate-adapted," meaning the body uses glucose as it's primary fuel.
Therefore, the ability of the liver and kidneys to “make new sugar” and regulate blood sugar levels is critical. The main advantage of this process is that it helps the body maintain steady blood sugar levels when foods containing carbohydrates or stored sugars (glycogen reserves) are unavailable.
Without gluconeogenesis, you wouldn't live very long, especially without food, as your body must have a constant and steady level of blood glucose to keep the brain and red blood cells going.
If you decide to stop eating, or you decide to follow a low carb ketogenic diet, carbohydrate intake drops. To make up for the missing carbohydrate in your diet, the liver creates the blood glucose it needs by breaking down the glycogen stored in your muscles and liver from your last meal. This process is called glycogenolysis.
After about 30 hours with no food, a great deal of this stored glycogen is broken down, and the body must then begin making glucose by breaking down stored fatty acids or amino acids from the protein in your muscles.
Some dietitians and trainers insist that this process is the reason that carbohydrates are "essential foods". They reason that people should eat lots of carbohydrates because otherwise, the liver will burn up muscle tissue trying to make enough glucose for the brain each day.
But this is not true when following a low carb diet. Once you reach a state of nutritional ketosis, your body can use ketones as a primary fuel, and make all the glucose it needs from the protein and fat that you eat.
In other words, if you eat enough protein each day to provide for body maintenance, it will provide enough amino acids for gluconeogenesis, and your muscles will stay intact. This has been confirmed in many studies.
Your body will burn your stored fat for fuel instead, and this is what everyone wants - to take fat out of storage in the fat cells, and burn it for fuel.
This is exactly what happens when you limit your carbohydrate intake.
Everyone experiences this process of gluconeogenesis constantly throughout the day, and especially at night while you sleep. Over the 6-9 hours that you are sleeping and not taking in food, your body is busily making new sugar to maintain its narrow blood sugar range.
For some people, this nightly process is so robust that morning blood sugar levels are higher than they were when the person went to sleep. This higher than normal morning blood sugar is called the Dawn Phenomenon, and is especially important to understand for Type 1 and insulin dependent Type 2 diabetics, as more insulin has to be injected to counteract the higher blood sugar overnight.
The bottom line is that there is no requirement for dietary carbohydrate, because your body can make all the glucose it needs from the protein that you eat, or from the glycerol released when fatty acids are broken down.
In fact, most metabolic syndrome health issues such as high blood pressure, high blood sugar, cholesterol imbalances, and high triglycerides are improved by reducing the amount of carbohydrates consumed.
One of the more recent myths surrounding ketogenic diets is that they are stressful to the body, because the internal process of having to make glucose from protein and glycerol causes a release of cortisol, the so called "stress" hormone.
This misconception arise from the incorrect belief that the process of GNG ALWAYS requires the secretion of cortisol.
There's a great discussion and breakdown of this myth here. The authors cite several references which report that cortisol is not released in the GNG process until blood sugar drops so low as to cause a hypoglycemic reaction.
And Peter over at the Hyperlipid blog mentions a study here that reports that ketogenic diets improve cortisol metabolism. He writes "Translation: LC eating is what is KEY to IMPROVING glucocorticoid metabolism."