Understanding How Do You Get Energy in Ketosis?

October 25, 2025 •

4 min read

In a metabolic state known as ketosis, your body becomes incredibly efficient at burning fat for energy, a process that relies on molecules called ketones. This radical shift in fuel source, which typically occurs by drastically reducing carbohydrate intake, allows your body and brain to run on a stable, long-lasting energy supply derived from dietary and stored fat.

Quick Summary

During ketosis, the body produces ketones from the breakdown of fat, which then serve as the primary energy source for most organs, including the brain. This metabolic adaptation provides a steady and efficient fuel supply when carbohydrates are restricted.

Key Points

Fat is the Fuel Source: In ketosis, your body burns fat for energy by producing molecules called ketones in the liver, replacing glucose as the primary fuel.
The 'Keto Flu' is Temporary: Initial fatigue and brain fog during the transition are normal and often caused by electrolyte imbalance and hydration changes as the body adapts to fat metabolism.
MCTs Offer a Quick Boost: Medium-chain triglycerides (MCTs), found in coconut oil, are quickly converted into ketones and provide a fast, efficient energy source.
The Body Can Still Make Glucose: Through a process called gluconeogenesis, the liver produces the small amount of glucose needed for certain cells from non-carbohydrate sources, ensuring no essential function is compromised.
Energy is More Stable in Ketosis: Unlike the highs and lows associated with glucose, ketones provide a steady and long-lasting energy supply, leading many to report increased mental clarity and sustained energy.
Mitochondrial Function May Be Enhanced: Research indicates that nutritional ketosis can lead to adaptations that improve mitochondrial efficiency, potentially reducing oxidative stress and boosting overall energy production.

The Shift from Glucose to Ketones

Under normal circumstances, the body’s cells use glucose as their primary fuel source, which is obtained from the carbohydrates we eat. In response to high blood glucose levels, the pancreas releases insulin, which helps transport glucose into cells for energy or storage as glycogen. However, when carbohydrate intake is significantly reduced, as with a ketogenic diet, the body’s glucose stores (glycogen) are depleted. With lower insulin levels and higher levels of hormones like glucagon, the body is signaled to turn to an alternative fuel source: fat.

The Process of Ketogenesis: From Fat to Fuel

The body's fat-burning process culminates in the production of ketones through a metabolic pathway called ketogenesis, which occurs primarily in the liver. Here is a step-by-step overview of how it works:

Release of Fatty Acids: When the body needs energy, it breaks down stored triglycerides (fats) into fatty acids and glycerol. This process, known as lipolysis, is upregulated when insulin is low.
Beta-Oxidation in the Liver: The fatty acids travel to the liver, where they are broken down into acetyl-CoA in the mitochondria through a process called beta-oxidation.
Ketone Body Formation: Under low-carb conditions, the liver doesn't have enough oxaloacetate to combine with all the acetyl-CoA to enter the Krebs cycle for energy production. As a result, the excess acetyl-CoA is converted into three different ketone bodies: beta-hydroxybutyrate (BHB), acetoacetate (AcAc), and acetone.
Fueling the Body: These ketones are released from the liver into the bloodstream to be used as fuel by the brain, heart, and skeletal muscles. The liver itself cannot use ketones for energy.

The Dual-Fuel System: Ketones and Gluconeogenesis

While ketones become the main energy source, the body still needs a small, constant supply of glucose for certain cells, like red blood cells, which cannot use ketones for fuel. The liver handles this need through a process called gluconeogenesis, or the "creation of new glucose". In ketosis, the liver efficiently produces this required glucose from non-carbohydrate sources, such as:

Glycerol, a byproduct of fat metabolism
Lactate, a molecule produced during intense exercise
Glucogenic amino acids, derived from protein breakdown

This dual-fuel system ensures the body meets all its energy requirements and prevents dangerously low blood sugar levels (hypoglycemia). Contrary to a common misconception, consuming adequate protein on a ketogenic diet will not disrupt ketosis, as gluconeogenesis is a tightly regulated, demand-driven process.

Navigating the Transition: The 'Keto Flu'

When first transitioning to a low-carb diet, many people experience temporary fatigue, headaches, and irritability known as the "keto flu". This is not a true illness but rather the body's adaptation period as it switches from glucose to fat metabolism. The symptoms are often caused by dehydration and a temporary loss of electrolytes, including sodium, potassium, and magnesium. These minerals play a crucial role in nerve and muscle function, and their depletion can cause cramps, dizziness, and low energy. To minimize the keto flu, it is vital to increase water intake and supplement with electrolytes.

Enhancing Ketogenic Energy

Once fully adapted, people in ketosis often report more stable and consistent energy levels throughout the day. Certain nutrients and strategies can further optimize this energy production:

Healthy Fats: Consuming a diet rich in healthy fats, such as avocados, olive oil, and nuts, is essential as fat is the primary fuel source in ketosis.
Medium-Chain Triglycerides (MCTs): MCTs, found in coconut oil, are rapidly absorbed and converted into ketones by the liver, providing a quick and efficient energy boost.
Exogenous Ketones: These are supplements that contain ketones (typically beta-hydroxybutyrate) and can temporarily elevate blood ketone levels. They can help reduce transition symptoms and provide an immediate energy source, but are not necessary for achieving nutritional ketosis.
Adequate Hydration and Electrolytes: Maintaining proper hydration and electrolyte balance is critical for energy, nerve function, and overall well-being in ketosis.

Ketosis vs. Carbohydrate Metabolism: Energy Comparison


Feature	Standard (High-Carb) Metabolism	Ketosis (High-Fat) Metabolism
Primary Fuel Source	Glucose derived from carbohydrates.	Ketones derived from dietary and stored fat.
Metabolic State	Insulin-dependent, with frequent blood sugar and energy fluctuations.	Insulin-stable, with low, steady blood sugar levels.
Energy Source	Quick energy bursts and crashes based on carbohydrate intake.	Long-lasting, stable energy derived from fat.
Brain Fuel	Primarily glucose, requiring about 120 grams per day.	Primarily ketones, meeting up to two-thirds of the brain's energy needs.
Liver's Role	Stores glucose as glycogen and performs gluconeogenesis when glucose is low.	Produces ketones from fatty acids (ketogenesis) and some glucose (gluconeogenesis).
Mitochondrial Health	Can be impacted by constant glucose fluctuations and oxidative stress.	Enhanced function and biogenesis reported in some tissues, potentially reducing oxidative stress.

Conclusion: Stable Energy and Mitochondrial Health

Transitioning to a ketogenic diet requires metabolic adaptation, but once your body becomes efficient at burning fat and ketones for fuel, you can experience a more stable, consistent energy supply. The key lies in understanding the shift from glucose to fat-based metabolism, which the liver facilitates by producing ketone bodies. By supporting this process with adequate hydration, electrolytes, and healthy fats, and managing the initial adaptation phase, individuals can overcome the temporary "keto flu" and potentially benefit from the long-term, sustained energy that ketosis offers, along with potential improvements in mitochondrial function. For more scientific detail on the metabolic pathways involved in ketogenesis, refer to resources like the National Center for Biotechnology Information (NCBI) Bookshelf.

Frequently Asked Questions

In ketosis, your body switches from using glucose (from carbohydrates) to using ketones, which are produced from the breakdown of fat, as its main energy source.

The liver produces ketones through a process called ketogenesis. When carbohydrate intake is low, the body breaks down fats into fatty acids, which the liver then converts into ketone bodies.

The initial period of low energy, often called the 'keto flu,' occurs as your body adapts to using fat instead of glucose for fuel. It is largely a result of temporary electrolyte imbalances and dehydration.

Yes. Once keto-adapted, the brain efficiently uses ketones for a significant portion of its energy needs, a crucial survival mechanism that is often associated with improved focus and clarity.

Yes, a small amount of glucose is still needed for specific functions and cells, such as red blood cells. The body produces this through gluconeogenesis, making glucose from non-carbohydrate sources.

Certain supplements can help. Medium-chain triglycerides (MCTs) can be converted to ketones quickly, and exogenous ketone supplements can also raise blood ketone levels to provide an immediate energy boost.

The adaptation period varies for each individual, but the initial keto flu symptoms typically last a few days to a couple of weeks. Once fully adapted, many people report more stable, long-lasting energy.