What are Ketones?

What are Ketones?

The goal of the ketogenic diet is to achieve ketosis. The word ketosis is formed by the word ketone plus the ending -osis, which is a Latin and Greek word that expresses a state or condition.

In other words, “ketogenic” and “ketosis” are based on the word ketone. Ketones are components that are generated primarily from fats and can be used by cells as a source of energy when carbohydrate intake is low [1].

In this article, we will discuss ketones in detail so you understand their role in your body, especially when you are on the keto diet.

What are Ketones?

Our bodies begin to produce ketones when we have gone without eating for several hours. This happens when we sleep, when we over-exercise, or when we are fasting [1].

While the ketogenic diet isn’t necessarily a “fast” in the sense of the common use of the word, you do stay away from carbohydrates.

The lack of carbohydrates, and therefore the lack of glucose, the body’s preferred source of energy, can make our body think that it is starving. Therefore, it turns to fat for energy – either from diet or from fat stored in our body. The product of fat metabolism to produce energy are ketones.

Types of Ketones

What are Ketones_the three types of ketones chemical formula_infographic_1

There are three main types of ketones: acetoacetate (AcAc), β-hydroxybutyrate (BHB), and acetone. They are all characterized as organic compounds with a carbonyl group [1].

Acetoacetate (AcAc)

Acetoacetate (AcAc) is a metabolite derived from butyrate [2]. AcAc is the “parent ketone” that produces the other two ketone bodies, acetone and β-hydroxybutyrate (BHB), though BHB can also produce acetoacetate [3].

β-hydroxybutyrate (BHB)

β-hydroxybutyrate (BHB) is a ketone body that is synthesized in the liver form fatty acids. When the glucose supply is low, it is an essential energy carrier to cells. In addition to providing energy, scientists have identified the role of BHB in cellular signaling and may activate certain genes and have an essential role in cellular function [4].

It is this pathway that lead scientists to hypothesize that BHB is responsible for the positive effects on the brain in people with diseases related to aging – like Alzheimer’s and Parkinson’s disease [4].


Acetone is formed from the spontaneous decarboxylation of AcAc. The levels of AcAc in the body are very low, as they are produced in small quantities. They are very volatile and, unlike the other two ketones, are not used by the body [3].

We excrete acetone through our urine and in our exhaled air. When you are in ketosis, you might notice that your breath smells sweet or fruity. Acetone is responsible for the fruity smell in your breath [3].

Ketone Formation

The production of ketone bodies can be divided into three steps: 1. The reverse of thiolase, the synthesis of HMG CoA, and 3) The reverse of HMG CoA [3].

They are produced mainly from the acetyl- CoA, mainly in liver cells, when carbohydrates are in low supply.

Functions of Ketones

Ketone bodies in diabetes

Diabetes is an illness that occurs where the body is unable to produce enough insulin, or when cells have a resistance to insulin. Insulin is needed to pass glucose into the cells [5].

When the glucose delivery process doesn’t work, cells signal the liver to start making ketones for energy.  However, some of the intermediary molecules are glucose-based, so if there isn’t a little bit of glucose available, this could cause ketoacidosis, which could be life threatening [5].

However, if the body is able to process at least some glucose, ketone bodies are used and ketoacidosis is avoided.

Ketone bodies during a restricted diet

In people without diabetes, ketone bodies are derived in the same way. They need intermediaries that are derived from glucose to produce ketone bodies. It is uncommon for healthy people to get experience ketoacidosis, and can maintain healthy levels of ketones. However, we need to make sure we are eating some carbohydrates (that is why the ketogenic diet requires that 5% of your energy come from carbohydrates) to make sure we are able to produce ketones.

Measuring Ketone Levels


There are three main ways to measure ketone levels in your body: through the blood, through urine, and through the breath.

Blood testing

Testing for ketones in the blood is the most accurate way to measure ketosis. It measures BHB, specifically, since it is the predominant ketone in the body. To do this, you can use a handheld device for home use, which will require you to prick your finger, but they are relatively expensive compared to the other two methods.

Urine testing

You can also test for ketones in your urine via urine strips. This method is low-cost and doesn’t require you to prick your fingers.

However, it is less accurate than blood testing.

Breath testing

This is the most uncommon form of measuring ketone levels in the blood. The apparatuses are relatively new to the market. However, since trials are still being performed to determine the accuracy of the breath testing, this isn’t the most recommended method.

Normal ketone levels

Normal ketone levels range between 0.6 and 3 mmol at any given time. Most healthy people will not go into ketoacidosis, thanks to normal feedback processes. If your ketone levels are higher than this, it is important to talk to your dietician to make sure you are eating a balanced diet.

Advantage of Ketones

What are Ketones_infographic_2

Ketones supply energy for the brain.

Large portions of the brain can use ketones for energy, especially when your body has adapted to a low-carb diet (about 60%) [6, 7]. Your body can make the missing glucose from protein via gluconeogenesis.

Ketones promote weight loss

Ketones are derived from fat, either from the diet, or from what is stored in our body. When it uses stored fat, we experience weight loss [8]. Additionally, people who are on the keto diet tend to feel less hungry, so they don’t feel restricted or deprived [9].

Ketosis can help boost heart health

Carb reduction may improve blood triglycerides, total cholesterol and HDL cholesterol [10].

May improve outcome of people with type 2 diabetes and metabolic syndrome

Low carb, high-fat diets can improve insulin sensitivity, and reduce the risk factors for metabolic syndrome [11, 12].

Ketone Risk, Side Effects and Management

While most cells in the body can use ketones for energy instead of glucose, there are cells in the liver and in the brain that still depend on glucose, even when adapted. For this reason, it is not healthy to eliminate carbohydrates completely. Reducing your carb intake to about 5% of your total energy needs supply glucose-dependent cells with the minimum carbohydrates their need to function without elevating blood glucose.

If you have type 2 diabetes and have taken on the keto diet to improve your outcome, it is very important to carefully monitor your ketone levels and glucose levels as you adopt a balanced ketogenic diet.

It is also important to note that the keto diet may not be for people with certain medical conditions, like liver diseases and type 1 diabetes.

Ketones: Verdict

Most of the body’s cells can easily adapt to using ketones for their energy needs. There are several advantages to a high-fat, low-carb diet for health, including weight loss, reduction in heart disease risk factors, and metabolic disorder risk factors, among others.

However, it is important to speak to your registered dietician and physician to determine if you have any medical conditions that would impede you from being healthy while taking on the ketogenic diet.


  1. New World Encyclopedia. Ketones in biology -
  2. Acetoacetate -
  3. Jnankumar C, Dr. Ketone Body Metabolism. -
  4. Newman J C, Verdin E. β-Hydroxybutyrate: A Signaling Metabolite. 2017, August -
  5. Biology Dictionary. What are Ketone Bodies -
  6. Hasselbalch SG, Knudsen GM, Jakobsen J, Hageman LP, Holm S, Paulson OB. Brain metabolism during short-term starvation in humans.1994, January -
  7. Owen OE, Morgan AP, Kemp HG, Sullivan JM, Herrera MG, Cahill GF Jr. Brain metabolism during fasting. 1967, October -
  8. Yancy WS Jr, Olsen MK, Guyton JR, Bakst RP, Westman EC. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: a randomized, controlled trial. 2004, May -
  9. Gibson AA, Seimon RV, Lee CM, Ayre J, Franklin J, Markovic TP, Caterson ID, Sainsbury A. Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. 2015, January -
  10. Volek JS, Sharman MJ, Forsythe CE. Modification of lipoproteins by very low-carbohydrate diets. 2005, June -
  11. Boden G, Sargrad K, Homko C, Mozzoli M, Stein TP. Effect of a low-carbohydrate diet on appetite, blood glucose levels, and insulin resistance in obese patients with type 2 diabetes. 2005, March -
  12. Feinman RD, Makowske M. Metabolic syndrome and low-carbohydrate ketogenic diets in the medical school biochemistry curriculum. 2003, September -

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