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Author: PhD Natalia Drabińska

When does the body reach a state of ketosis? What does it mean? Is it safe? These are questions often asked by people who decide to follow a ketogenic diet.

Ketosis is a metabolic state in which the energy is obtained from metabolism of fatty acids, not glucose, leading to increased level of circulating ketone bodies.

Under normal conditions, our body uses sugars, specifically glucose, as its main source of energy. When glucose is depleted, the body switches to obtaining energy from other sources in the processes of gluconeogenesis and ketogenesis. In gluconeogenesis, the body (mainly the liver) obtains glucose from substrates other than carbohydrates, such as amino acids, glycerol or lactic acid. However, when the lowered level of glucose persists for longer, the metabolism must switch to alternative energy sources, including fat. In the case of ketosis, ketone bodies (beta-hydroxybutyric acid, acetoacetic acid and acetone) derived from the breakdown of fatty acids become the main source of energy in the process of ketogenesis. Interestingly, ketone bodies are not the same as ketones. From a chemical point of view, only acetone can be classified as ketone, while the remaining compounds, despite having a ketone group, belong to hydroxy acids and keto acids, respectively [1].

When does the body reach a state of ketosis?

The state of ketosis occurs not only during the ketogenic diets but also during a long break in eating, such as in the morning, immediately after waking up, as well as after intense physical exercise. After an overnight fasting, ketone bodies cover about 2-6% of energy needs, and after 3 days of fasting, this level can increase to even 40%. The state of ketosis lasts as long as the body does not receive carbohydrates.

In extreme cases, increased production of ketone bodies to a level of above 25 mmol/L can lead to ketonemia and ketoacidosis, but this occurs mainly in people with diabetes and is not possible to achieve after using a ketogenic diet by a healthy person. In contrast to ketoacidosis, during nutritional ketosis, a slightly elevated level of ketone bodies (> 0.5 mmol/L) is observed in the bloodstream with simultaneous low and stable glucose and insulin levels. Since the concentration of ketones is kept low, it is a safe process and does not lead to a change in the pH of the blood. Therefore, in people using the ketogenic diet, there is no risk of the so-called “acidification of the body”. Our blood buffer system copes well with even elevated levels of ketone bodies.

The level of ketone bodies in the body is regulated by two processes: the production of ketone bodies (ketogenesis) and their degradation (ketolysis), which are controlled by insulin and glucagon. Glucagon accelerates the production of ketone bodies, and insulin slows down this process [1].


The time needed to reach ketosis is an individualized process and depends on many factors, including:

  • age
  • daily physical activity
  • BMI
  • metabolism
  • stress level
  • type of diet prior to a ketogenic diet

If you were consuming large amounts of carbohydrates before starting the ketogenic diet, it may take longer to reach ketosis due to the large stores of glucose in the body that must be exhausted before the initiation of using ketone bodies.

From an energy point of view, ketone bodies provide more energy. Taking adenosine triphosphate (ATP) as the basic energy unit of the body, it can be assumed that 100 g of glucose provides 8700 g of ATP, while 100 g of beta-hydroxybutyric acid and acetoacetic acid provide 9400 and 10500 g of ATP, respectively. Therefore, during the ketogenic diet, despite the caloric deficit, we do not feel a decrease in energy.

Another way to achieve a state of ketosis is supplementation with exogenous ketone bodies. It is mainly used in sports to improve endurance performance. Taking supplements containing exogenous ketone bodies induces a state of nutritional ketosis in a few minutes without the limitation of carbohydrates in the diet [2,3].

When we measure the level of ketones in the bloodstream, it corresponds mainly to the concentration of beta-hydroxybutyric acid and acetoacetic acid. Acetone, which is a very volatile compound, is excreted from the body very quickly with breath or urine. Hence, in people who are in ketosis, breath and urine can have a specific, sweetish smell.


  • 1. Circulating ketone bodies measurement

The most reliable method of ketosis analysis is to measure the concentration of ketone bodies (mainly beta-hydroxybutyrate) in the bloodstream. Currently, there are many models of devices for the self-measurement of ketone bodies, similar to glucometers, available on the market. This involves pricking your finger with a lancet and applying the sample to the test strip. This method is quite expensive and requires unpleasant finger pricking.

  • 2. Breath ketone bodies measurement

The measurement of ketones in the breath is an alternative to repeated punctures. It only requires blowing for a certain amount of time into the mouthpiece to read a result. Cheaper models of devices are not very precise and allow you to determine the level of ketone bodies at levels: none, low or high. To get a more precise result, more money needs to be invested in the analyzer. The main problem with the breath analysis is that it shows the content of acetone, which is not the main ketone body. Hence, the result may be not so precise.

  • 3. Urinary ketone bodies measurement

By far the most popular and least invasive method of measuring ketone bodies is the use of urine test strips. Depending on the concentration of ketones in the urine, the colour of the strip changes, which can be compared to the attached scale. Although this method is not very precise, it allows you to control the state of ketosis daily in a quick and cheap way.


[1] Drabińska, N., Wiczkowski, W., Piskuła, M.K. (2021) Recent advances in the application
of a ketogenic diet for obesity management. Trends in Food Science & Technology, 110: 28-38.

[2] Shaw, D.M., Merien, F., Braakhuis, A. et al. (2020) Exogenous Ketone Supplementation
and Keto-Adaptation for Endurance Performance: Disentangling the Effects of Two Distinct
Metabolic States. Sports Med 50, 641–656.

[3] Poff, A.M., Koutnik, A.P., Egan, B. (2020). Nutritional Ketosis with Ketogenic Diets or
Exogenous Ketones: Features, Convergence, and Divergence. Current Sports Medicine
Reports 19(7), 251-259.

Phd Natalia Drabińska

PhD Natalia Drabińska is a talented and outstanding scientist specializing in the field of nutrition and biotechnology. She obtained her PhD degree from the Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences in Olsztyn, where her interdisciplinary doctoral thesis focused on the use of fructooligosaccharides and inulin as a dietary component for children with celiac disease.

Currently, she works as an assistant professor at the Poznan University of Life Sciences and at the Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences, where she is involved in many research projects related to metabolism, inflammation, and ketogenic diets. She is also a member of several scientific societies, including the Polish Metabolomics Society and the European Federation of Food Science and Technology.

PhD Natalia Drabińska is a passionate and dedicated researcher whose results help to better understand the impact of nutrition on the human body.

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