What Are Ketones?

What They Do, How to Test, and What Results Mean

Ketones, or keto acids, are compounds produced by the liver as an alternative form of energy when the body is low on glucose (sugar).

Three ketones—acetoacetate (AcAc), beta-hydroxybutyric acid (BB), and acetone—are produced in the liver from free fatty acids (FFAs). The body is constantly producing small amounts of ketones to use for energy when fasting or sleeping and during long periods of exercise. 

Ketosis occurs when ketone production is increased because of decreased carbohydrates and increased fatty acids. For example, people following a strict ketogenic diet (a very low carb diet) rely on ketones for energy.

High vs. Low Ketones - Illustration by Danie Drankwalter

Verywell / Danie Drankwalter

However, in people with certain health conditions, such as type 1 diabetes, high levels of ketones can result in diabetic ketoacidosis (DKA), a life-threatening condition if not treated right away.

Learn more about ketone formation, testing for ketones, and what these levels mean.

What Are Ketones?

After fasting or following a very low carbohydrate diet for some time, the body is deprived of glucose and insulin levels are lowered, which forces the body to burn fat for fuel from ketones.

As a result, an abundance of the molecule acetyl-CoA leads to the formation ketones—beta-hydroxybutyric acid, acetoacetate, and acetone—in a process known as ketogenesis.

Ketone Formation

When the body is provided with enough carbohydrates or can utilize stored carbohydrates (from glycogen), it uses them to create glucose, the body's preferred energy source. This process is referred to as glycolysis and glycogenolysis.

Glucose can also be created by a process called gluconeogenesis, which produces glucose from noncarbohydrate sources such as lactate.

However, when the body is low on carbohydrates or glucose and does not have any in storage, it forms ketones to use as energy. Strictly limiting carbohydrate intake to less than 50 grams or even 20 to 30 grams per day and increasing fat intake to about 70% to 80% of total calories can cause ketone formation. The body is able to use ketones as fuel because ketones cross the blood-brain barrier (part of the central nervous system) and fatty acids do not.

Ketones can also be created in people with diabetes for a variety of reasons. For example, ketones can form in people when blood sugars are elevated and they are lacking insulin (as in times of illness or missed insulin doses) or in people with normal blood sugars who are ill and take SGLT-2 inhibitors (prescription medications used to help lower blood sugar).

Testing Ketones

People with diabetes are often prescribed ketone testing strips. Testing for ketones can be done with urine or blood tests. You can detect ketones in the blood before they reach the urine. Early detection and treatment of ketones in people with diabetes can reduce the risk of an emergency, therefore clinicians usually recommend a blood ketone meter, an at-home test kit.

However, if you are monitoring your ketones for other reasons, or you cannot afford a blood ketone meter and test strips, you can also test for ketones through the urine.

Ketones in Urine

Results range from 0 (not detected) to +4 (high amount detected). If you are using an at-home testing kit, you will dip your test strip into your urine and compare the color to the color on the bottle. Typically, any color other than beige is an indication that there are ketones in your urine.

Ketones in Blood

Blood ketone meters are prescribed to people with diabetes to monitor their ketones levels accurately. A normal level of ketones is below 0.6 mmol/L. Any level higher than this, indicates ketones are present.

Understanding Ketone Levels

Ketone levels vary from person to person. For example, dietary intake, including carbohydrates, protein, and fat intake can influence ketone levels. Experts recommend regular ketone measurements to provide valuable feedback to personalize diets. Low levels of ketones in healthy individuals usually are not a problem, but elevated ketone levels in people with underlying health conditions, such as diabetes, can be very dangerous.

High Ketone Levels

High ketone levels are typically not a problem when inducing nutritional ketosis in healthy individuals, because insulin is able to regulate glucose levels and a normal pH level is maintained. However, high ketone levels in people with diabetes is a medical emergency as it can result in DKA.

Experts suggest that the range of ketones present in DKA is fivefold to tenfold greater than the levels achieved during nutritional ketosis. DKA can present with symptoms such as increased thirst, fatigue, urination, stomach pain, fruity breath, rapid, shallow breathing, vomiting, and nausea.

Nondiabetic ketoacidosis is another risk of having high ketone levels. Although this condition is rarely caused by low-carbohydrate diets, people with other health conditions or those who experience illness such as seasonal flu are at higher risk.

Low Ketone Levels

The human body produces a small number of ketones after a period of not eating or fasting. This is not an indication that the body is utilizing ketones for fuel. However, in people with diabetes, low levels of ketones or trace amounts of ketones, with high glucose levels, may indicate that a person needs more insulin.

For people following a ketogenic diet, levels of ketones can fluctuate depending on their dietary intake. If you are trying to establish a state of nutritional ketosis and are eating too much protein, protein will be metabolized into glucose and reduce ketone production.

Discuss with your healthcare provider changes to your diet before starting any diet. People with type 1 diabetes, those with a history of disordered eating (abnormal eating behavior), and people who are pregnant or breastfeeding should avoid ketogenic diets.

Summary

Ketones are formed as a source of energy when the body is low on glucose. In healthy individuals who do not have any issues with insulin function, nutritional ketosis is usually not a dangerous condition. However, in people with diabetes, the presence of ketones can increase the risk of DKA, which can be life-threatening if not treated.

If you are looking to achieve a level of nutritional ketosis, you should know that the long-term effects of this diet are not well understood, and you may need additional nutritional support.

A Word From Verywell 

If you are following a ketogenic diet to induce nutritional ketosis, you will want to know what your ketone levels are. In addition, if you have a medical condition such as diabetes or a neurological condition in which a ketogenic diet has been prescribed, you can manage your ketone levels by testing them in your urine or blood. Blood ketone meters are typically preferred.

People with established diabetes should monitor their levels of ketones when blood sugars are elevated or if they are on an SGLT-2 inhibitor and are experiencing symptoms of DKA. If you have diabetes, make sure you have access to your medical team at any time of day.

Frequently Asked Questions

  • What will happen if my ketone levels are too high?

    If your ketone levels are too high and you have diabetes, you can develop diabetic ketoacidosis. If this condition is left untreated, it can be fatal. If you do not have diabetes and your ketone levels are too high your body will compensate and maintain homeostasis. The long-term effects of high ketone levels are not well understood, and more research is needed.

  • What is ketoacidosis?

    Ketoacidosis occurs because of acidosis, meaning there is too much acid in bodily fluids. Ketoacidosis usually occurs in people with diabetes who rely on insulin to regulate their blood sugars, but it can also occur in periods of starvation. The ketogenic diet is not advised for people who are pregnant, lactating, or have type 1 diabetes.

  • What do ketones smell like?

    Ketones are often said to smell fruity or like nail polish remover. This is because they contain acetone, which has a sweet odor.



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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Barbie Cervoni MS, RD, CDCES, CDN
Barbie Cervoni MS, RD, CDCES, CDN, is a registered dietitian and certified diabetes care and education specialist.