Gluconeogenesis is the process of synthesizing glucose in the body from non-carbohydrate precursors. It is the biosynthesis of new glucose, not derived from the consumption of carbohydrate. Very simply put, it is often the conversion of protein or fat to sugar for the body to use as fuel.
Gluconeogenesis occurs in the liver and the kidneys and can be seen as the reverse anabolic process of glycolysis, the breakdown, and extraction of energy from glucose.
Why Your Body Needs Glucose
Glucose is the major source of energy for the body and the brain. Even at rest, our bodies need energy to function.
For example, the brain alone uses as much as 100 grams of glucose a day. When we are active, our bodies (particularly the working muscles) need even more. Glucose is the body's preferred source of fuel because it can be quickly used for energy.
Energy from glucose can be quickly created through a complex ten-step process called glycolysis. During glycolysis, glucose is split into smaller molecules (called pyruvate) for use as energy throughout the body.
Gluconeogenesis ensures that in the absence of glucose from glycolysis that critical limits of glucose are maintained when carbohydrate is absent.
Your body's preferred energy source is glucose. Your body may use either the process of glycolysis or the process of gluconeogenesis to provide your body and your brain with the energy it needs to function.
Glucose on a Normal Diet vs. Low Carb Diet
If you were consuming a typical American diet, your body gets plenty of glucose from the food you consume. For example, starches (plentiful in grains including flour, potatoes, etc.) are essentially long chains of glucose.
In addition, naturally-occurring sugars (in foods like fruit) and added sugars (found in many processed foods) are plentiful in the diets of most people. These foods boost glucose levels.
However, starchy and sugary foods are limited on a low carb diet. If carbohydrate is not being consumed, the body needs to make glucose from other sources.
Gluconeogenesis is a workaround your body's metabolism to get and maintain the energy it needs to conduct normal bodily functions.
People on a low-carb diet have less glucose available for energy because there is less carbohydrate consumed. Gluconeogenesis is the body's way of providing energy to the body when glucose is not supplied through the diet.
How Gluconeogenesis Works
The process of gluconeogenesis takes place primarily in the liver, where glucose is made from amino acids (protein), glycerol (the backbone of triglycerides, the primary fat storage molecule), and glucose metabolism intermediaries like lactate and pyruvate.
As previously mentioned, gluconeogenesis may occur when you are on a low-carb diet. It can also happen during periods of fasting, starvation, or during intense exercise. It may also happen when you consume excess protein.
The complex process is a series of chemical conversions. A very simple explanation might involve three steps.
- Step one involves the conversion of pyruvate to phosphoenolpyruvic acid (PEP). PEP is an ester, or a chemical compound derived from acid.
- Step two is essentially glycolysis in reverse. It involves the conversion of PEP to another compound called fructose-6-phosphate, a derivative of fructose.
- Step three is the conversion of fructose-6-phosphate to glucose.
Gluconeogenesis vs. Ketosis
Those on a very low carb diet are often familiar with a metabolic state called ketosis. Ketosis is another way of providing fuel to the body if not enough glucose is present. But ketosis is a metabolic state that differs from the process known as gluconeogenesis.
During ketosis, the body essentially learns to use fat as fuel rather than glucose. When you are in this state, your energy supply comes from ketone bodies circulating in the blood. Ketone bodies are produced through a process called ketogenesis which happens in the mitochondria of liver cells.
Ketogenesis and gluconeogenesis are similar in that they are both chemical processes that provide energy to the body when not enough carbohydrate is present in the diet. However, ketogenesis differs in that it produces ketones to be used as fuel, rather than glucose.
Ketogenic diets are low-carb, high-fat eating plans designed to put your body into a state of ketosis. These diets (also known as "keto" diets) are sometimes prescribed for people with certain neurological disorders.
For example, there is some scientific evidence to show that ketogenic diets may help people with epilepsy and other conditions including Parkinson and Alzheimer disease.
Some athletes and people looking to lose weight also follow ketogenic diets. However, the eating program can be very difficult to maintain.
Additionally, if you consume a lot of protein on your keto eating plan, gluconeogenesis may prevent ketogenesis from occurring. That is, your body will use protein to create glucose, instead of converting fat to fuel. In fact, during the first few days of a ketogenic diet, your body is likely to use gluconeogenesis to produce energy.
To know for sure if and when your body has shifted from gluconeogenesis to a state of ketosis, people who follow the diet use various methods to test for the presence of ketone bodies.