What Are Ketones? Function, Test, and Normal Levels

Understanding the role of ketones in the body is crucial for individuals looking to optimize their health, especially those who want to venture into the keto diet or those with diabetes.

In this comprehensive guide, we’ll delve into the various aspects of ketone bodies, from their formation to testing methods and what high ketone levels might indicate.

Key Takeaways:

  • The liver produces ketones in the absence of carbohydrates or during fasting.
  • They are an energy source for organs and muscles broken down from fat.
  • Normal ketone levels are below 0.6 mmol/L and 1.0 – 3.0 mmol/L indicates ketosis.
  • Above 3.0 mmol/L can be a health risk for people with diabetes.

Table of Contents:

What Are Ketones?

Ketones are organic compounds produced by the liver through the breakdown of fats.

In essence, when the body faces a scarcity of its primary energy source, glucose, as in a keto diet, it shifts to utilizing stored fats for fuel.

This metabolic process, known as ketogenesis, results in the formation of ketone bodies.

The three main types of ketones produced are beta-hydroxybutyric acid (BHB), acetoacetate (AcAc), and acetone.1

What Do Ketones Do in the Body?

Ketones are crucial in providing an alternative energy source when glucose is limited. The primary beneficiaries of ketones are the brain and muscles.2

Normally, the brain relies heavily on glucose for energy, but ketones become a valuable substitute in the absence or shortage of glucose.

The brain can efficiently use ketones as an energy source, helping maintain cognitive function during glucose scarcity. This benefit is true even for people with neurodegenerative diseases.3

They also support the energy needs of various muscles and tissues. Aside from that, ketone bodies play pivotal roles as signaling mediators, drivers of protein post-translational modification (PTM), and modulators of inflammation and oxidative stress.

How Ketone Bodies Are Formed

The liver forms ketone bodies4 when there is not enough glucose for energy.

The process of ketogenesis involves the breakdown of stored fats into fatty acids, which are then further converted into ketones.

The liver releases ketone bodies into the bloodstream, making them accessible to various tissues for energy production.

Beta-hydroxybutyric acid (BHB) is the predominant and most efficiently utilized form among the ketones produced. This compound is a potent energy source for the body and is often the primary component in exogenous ketone supplements.

What Are Exogenous Ketones?

Exogenous ketones are external sources of ketone bodies available in supplement form.

These supplements typically contain beta-hydroxybutyric acid (BHB), the most abundant and readily usable ketone. The primary purpose of exogenous ketones is to elevate blood ketone levels, facilitating a quicker transition into ketosis.5

While endogenous ketones are produced naturally within the body during fasting or carbohydrate restriction states, exogenous ketones provide a shortcut to achieving and maintaining ketosis.

This might be particularly beneficial for individuals following a ketogenic diet.

It’s important to note that while exogenous ketones can be helpful, they are not a substitute for a well-formulated ketogenic diet.

What Are the Symptoms of High Ketones?

High levels of ketones, a condition known as ketoacidosis, can manifest with distinctive symptoms. Recognizing these symptoms is crucial, especially for individuals with diabetes or those following ketogenic diets. The symptoms include:

  • Keto Flu: High ketones can impair energy metabolism, causing feelings of fatigue and weakness even with rest. You may also experience headaches, foggy brain, and nausea.
  • Excessive Thirst and Urination: High ketone levels can lead to dehydration, triggering an increased sensation of thirst as the body attempts to compensate for fluid loss, resulting in increased urine production.
  • Keto Breath: A distinctive fruity or sweet odor in the breath, often described as “keto breath,” is a characteristic sign of elevated ketones.
  • Stomach Pain: Abdominal pain may occur due to the metabolic imbalance caused by high ketone levels.
  • Muscle Cramps: Electrolyte imbalance may occur with frequent urination, often causing muscle cramps.
  • Hyperventilation: Too many ketones make the blood acidic, and your lungs are trying to compensate by letting the acid out via exhalation.

What Tests Check Ketone Levels?

ketones on a testing device

Urine Tests

  • Description: Urine tests involve using ketone test strips that change color based on the ketone concentration in urine.
  • Limitations: While convenient, urine tests offer only a snapshot of ketone levels and may not accurately reflect current levels.

Blood Tests

  • Description: Blood tests measure the concentration of ketones in the bloodstream, providing a more accurate and real-time assessment. You can complete this in a laboratory or at-home ketone test kit.
  • Accuracy: Blood tests are considered more accurate than urine tests and are recommended for precise ketone measurement.

Breathalyzer Tests

  • Description: Breathalyzer tests measure acetone levels in the breath using a piece of handheld equipment that you blow into to measure the ketone level.
  • Limitations: Breathalyzer tests are still under study, and their reliability and accuracy may vary. They are not yet considered a primary method for ketone assessment.

Who Should Test Ketones?

Ketone testing is particularly relevant for specific individuals, and understanding who should monitor their ketone levels is crucial. Here’s a breakdown of those who should consider regular ketone testing:

Individuals on the Ketogenic Diet or Intermittent Fasting

Tracking ketones ensures that the body effectively utilizes fats for energy, contributing to the diet’s success. Most people should have their ketones at 0.5 – 3.0 mmol/L.6

People with Diabetes

Individuals with type 1 diabetes lack insulin production, making them prone to diabetic ketoacidosis (DKA) when ketones become elevated. Experts suggest that ketone levels should stay under 0.6 mmol/L.

Athletes and Fitness Enthusiasts

Ketone testing can be a performance metric for those taking exogenous ketones, indicating the efficiency of fat adaptation during exercise. Users should expect a 300% increase in ketone levels7 when taking exogenous ketones.

When Should I Check My Ketone Levels?

Determining the timing for ketone testing depends on various factors, including individual goals and circumstances. Here are situations when checking ketone levels is advisable:

  • When Initiating a Ketogenic Diet: Regular testing helps confirm the onset of ketosis and provides insights into dietary adjustments.
  • After a Period of Fasting or Intermittent Fasting: Checking ketone levels verifies the success of the fasting state.
  • During Illness or Stress: Illness or stress can impact blood sugar levels and ketosis.
  • Regular Monitoring for Diabetics:
    • Type 1 Diabetes: Individuals with type 1 diabetes should test ketone levels during illness, high blood sugar, or if advised by their healthcare provider.
    • Type 2 Diabetes: As Advised, those with type 2 diabetes may test ketones based on their healthcare provider’s recommendations, especially during periods of uncontrolled blood sugar.

What Do Ketone Test Results Mean?

Understanding the significance of different blood ketone levels is crucial. Here’s a guide to help you determine your current state:

  • Normal Ketone Levels: Less than 0.6 mmol/L. Indicates that the body is utilizing fats for energy within a healthy and controlled range.
  • Slightly High Ketone Levels: 0.6 – 1.0 mmol/L suggest a transition into ketosis.
  • Moderately High Ketone Levels: 1.0 – 3.0 mmol/L indicate a deeper state of ketosis. Close monitoring is advisable, especially for those with diabetes.
  • Very High Ketone Levels: Above 3.0 mmol/L raises concerns about ketoacidosis, especially in individuals with diabetes.


Understanding ketones and their role in the body is essential for individuals managing diabetes or exploring the benefits of a ketogenic lifestyle.

Regular monitoring and prompt medical intervention ensure a proactive approach to health.

Frequently Asked Questions (FAQ)

What does it mean if your ketones are high?

High ketone levels mean that your body is in a state of ketosis, which may benefit people on the keto diet. However, very high ketone levels are not ideal, especially for those with diabetes.

What are ketones in a diabetic?

In individuals with diabetes, ketones result from the breakdown of fats when there is insufficient insulin to process glucose. Monitoring ketone levels is crucial to prevent complications such as ketoacidosis.

What is a normal ketone level?

A normal blood ketone level is generally less than 0.6 mmol/L. Elevated levels may suggest intervention, while very high levels indicate a potential emergency.

Is 4.0 ketones good?

A ketone level of 4.0 mmol/L is considered very high and may indicate a risk of diabetic ketoacidosis. Immediate medical attention is advised in such cases.


1Laffel L. (1999). Ketone bodies: a review of physiology, pathophysiology and application of monitoring to diabetes. Diabetes/metabolism research and reviews, 15(6), 412–426. https://doi.org/10.1002/(sici)1520-7560(199911/12)15:6<412::aid-dmrr72>3.0.co;2-8

2Puchalska P, Crawford PA. Multi-dimensional Roles of Ketone Bodies in Fuel Metabolism, Signaling, and Therapeutics. Cell Metab. 2017 Feb 7;25(2):262-284. doi: 10.1016/j.cmet.2016.12.022. PMID: 28178565; PMCID: PMC5313038.

3Jensen NJ, Wodschow HZ, Nilsson M, Rungby J. Effects of Ketone Bodies on Brain Metabolism and Function in Neurodegenerative Diseases. Int J Mol Sci. 2020 Nov 20;21(22):8767. doi: 10.3390/ijms21228767. PMID: 33233502; PMCID: PMC7699472.

4Cantrell, C. B., & Mohiuddin, S. S. (2023). Biochemistry, Ketone Metabolism. In StatPearls. StatPearls Publishing.

5Falkenhain, K., Islam, H., & Little, J. P. (2023). Exogenous ketone supplementation: an emerging tool for physiologists with potential as a metabolic therapy. Experimental physiology, 108(2), 177–187. https://doi.org/10.1113/EP090430

6Gershuni VM, Yan SL, Medici V. Nutritional Ketosis for Weight Management and Reversal of Metabolic Syndrome. Curr Nutr Rep. 2018 Sep;7(3):97-106. doi: 10.1007/s13668-018-0235-0. PMID: 30128963; PMCID: PMC6472268.

7James, S., & Kjerulf Greer, B. (2019). Influence of Exogenous β-Hydroxybutyrate on Walking Economy and Rating of Perceived Exertion. Journal of dietary supplements, 16(4), 463–469. https://doi.org/10.1080/19390211.2018.1471562

Mag. Stephan Lederer, MSc.

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

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