The human body has an impressive ability to maintain stable blood sugar levels, even when you haven’t eaten for hours or are following a low-carbohydrate diet. One of the key processes that makes this possible is gluconeogenesis.

Gluconeogenesis is the body’s method of producing new glucose when dietary carbohydrates and stored glycogen are not enough to meet its energy needs. This natural metabolic process helps ensure that vital organs and tissues continue to function properly, even during fasting or prolonged exercise.

What Does Gluconeogenesis Mean?

The word gluconeogenesis comes from three Greek roots:

• Gluco refers to glucose (sugar).
• Neo means new.
• Genesis means creation or production.

Together, gluconeogenesis literally means “the creation of new glucose.”

Unlike digesting carbohydrates from food, gluconeogenesis creates glucose from non-carbohydrate substances already present in the body.

Why Is Gluconeogenesis Important?

Glucose is the body’s primary source of energy for many cells. Although fat and ketones can provide fuel for many tissues, some cells require glucose to survive.

These include:

• Red blood cells
• Parts of the brain
• Certain cells in the kidneys
• Portions of the nervous system

Without gluconeogenesis, blood sugar levels could drop too low during periods without food, potentially leading to symptoms such as weakness, dizziness, confusion, and in severe cases, loss of consciousness.

Where Does Gluconeogenesis Occur?

Gluconeogenesis takes place primarily in the liver, which is the body’s main glucose-producing organ.

The kidneys also perform gluconeogenesis, especially during prolonged fasting or starvation, when they contribute a greater share of glucose production.

These organs release newly formed glucose into the bloodstream to help maintain normal blood sugar levels.

What Does the Body Use to Make Glucose?

Gluconeogenesis relies on three main sources of raw materials.

Amino Acids

Amino acids are the building blocks of protein.

When the body needs additional glucose, certain amino acids can be converted into glucose after their nitrogen component is removed.

Most amino acids are classified as glucogenic, meaning they can contribute to glucose production.

Lactate

Lactate is produced by muscles and red blood cells, especially during intense exercise.

Rather than being wasted, lactate travels to the liver, where it is converted back into glucose through a process known as the Cori cycle.

Glycerol

When stored body fat is broken down, it produces:

• Fatty acids
• Glycerol

While fatty acids cannot be converted into glucose in humans, glycerol can enter the gluconeogenesis pathway and become glucose.

What Cannot Be Converted Into Glucose?

Many people assume that fat can simply be turned into glucose, but this is only partly true.

The glycerol portion of fat can become glucose.

However, the fatty acids themselves cannot be converted into significant amounts of glucose. Instead, they are typically used directly for energy or converted into ketone bodies.

Similarly, two amino acids—leucine and lysine—are purely ketogenic and cannot be converted into glucose.

How Does Gluconeogenesis Work?

Although the process involves many biochemical reactions, it can be understood in a few basic steps.

Step 1: Raw Materials Reach the Liver

The liver receives glucogenic amino acids, lactate, and glycerol through the bloodstream.

Step 2: Conversion Into Intermediate Compounds

These substances are transformed into molecules such as pyruvate or oxaloacetate, which are important intermediates in energy metabolism.

Step 3: Glucose Formation

The liver uses specialized enzymes to assemble these intermediates into glucose.

Step 4: Release Into the Bloodstream

The newly produced glucose is released into the bloodstream, where it becomes available to tissues that need it.

When Does Gluconeogenesis Occur?

Gluconeogenesis happens continuously at a low level, but it becomes much more active when glucose supplies begin to decline.

During Fasting

Several hours after eating, liver glycogen stores begin to decrease.

As glycogen becomes less available, gluconeogenesis increases to maintain blood sugar.

Overnight

Even while sleeping, the body continues using glucose.

As the overnight fast continues, gluconeogenesis gradually contributes more to maintaining blood glucose levels.

During Low-Carbohydrate Diets

When carbohydrate intake is significantly reduced, the body adapts by increasing glucose production from non-carbohydrate sources.

This helps supply tissues that still require glucose while the body burns more fat for energy.

During Prolonged Exercise

Long-duration exercise can deplete glycogen stores.

As these stores decline, gluconeogenesis helps maintain blood sugar and support ongoing physical activity.

During Starvation

In prolonged starvation, gluconeogenesis becomes increasingly important.

Initially, amino acids provide much of the raw material for glucose production. As starvation continues, ketone production rises, allowing the brain to rely more on ketones and reducing the need to break down muscle protein.

How Is Gluconeogenesis Different From Glycogenolysis?

These two processes are often confused, but they are different.

Glycogenolysis is the breakdown of stored glycogen into glucose.

Gluconeogenesis creates entirely new glucose from non-carbohydrate substances.

Both processes help maintain blood sugar, but glycogenolysis usually provides glucose first because it is faster. Once glycogen stores become depleted, gluconeogenesis becomes increasingly important.

Which Hormones Regulate Gluconeogenesis?

Several hormones control when the body makes glucose.

Glucagon

Glucagon is released when blood sugar falls.

It signals the liver to increase glucose production through both glycogenolysis and gluconeogenesis.

Insulin

Insulin has the opposite effect.

After eating, insulin suppresses gluconeogenesis because glucose from food is readily available.

Cortisol

Cortisol increases gluconeogenesis during prolonged stress, illness, or fasting by promoting the release of amino acids from protein.

Epinephrine

Also known as adrenaline, epinephrine stimulates glucose production during exercise and stressful situations to provide additional energy.

Is Gluconeogenesis Harmful?

No. Gluconeogenesis is a normal and essential metabolic process.

Without it, the body would struggle to maintain healthy blood sugar levels between meals or during fasting.

However, excessive gluconeogenesis can contribute to elevated blood sugar in certain medical conditions, particularly type 2 diabetes. In people with insulin resistance, the liver may continue producing glucose even when blood sugar is already high, worsening hyperglycemia.

Common Misconceptions About Gluconeogenesis

Several myths surround this metabolic process.

One common misconception is that eating protein automatically causes all of it to become glucose. In reality, the body converts only the amount of amino acids needed to maintain normal blood sugar and meet energy demands.

Another misconception is that gluconeogenesis only happens during starvation. While it becomes more active during prolonged fasting, it occurs every day to some degree, including overnight while you sleep.

Some people also believe that gluconeogenesis is a sign that the body is “breaking down muscle.” Although muscle protein can supply amino acids during extended fasting or illness, dietary protein also provides amino acids, and the body has mechanisms to reduce muscle breakdown whenever possible.

Final Thoughts

Gluconeogenesis is the body’s process of creating new glucose from non-carbohydrate sources such as amino acids, lactate, and glycerol. It occurs mainly in the liver and, to a lesser extent, the kidneys, helping maintain stable blood sugar when dietary carbohydrates or stored glycogen are unavailable.

This highly regulated process ensures that glucose-dependent tissues continue receiving the fuel they need during fasting, exercise, low-carbohydrate intake, and other situations where glucose demand exceeds the available supply. Far from being a backup system used only in emergencies, gluconeogenesis is an essential part of normal metabolism that supports health every day.