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What is ketosis and what are its symptoms?

Ketosis is a metabolic state in which the body obtains energy from fatty acids, whereas normally the main source of energy is glucose. The state of ketosis is particularly desirable for people losing weight - it is synonymous with the efficient burning of the body's own fat and protein. How do you achieve ketosis? When can we speak of a state of ketosis? Answers to these and other related questions can be found below.

Ketosis – what is it?

Ketosis occurs as a result of an increase in the level of ketone bodies in the blood (so-called forced synthesis), caused among other things by a reduction in insulin levels and the breakdown of fatty acids. The source of energy in a state of ketosis is derived from fatty tissues: as a consequence of the lack of glucose, the body switches to using other sources in the processes of gluconeogenesis and ketogenesis.

In the process of gluconeogenesis, the body attempts to obtain glucose from, among other sources, amino acids, glycerol and lactic acid. When such a state is prolonged, energy is obtained from alternative sources, such as fat. In the case of ketosis, the main energy source is ketone bodies, derived from the breakdown of fatty acids. [1]

What are the symptoms of ketosis?

Ketosis is a metabolic state, the achievement of which is associated with numerous benefits, but requires going through a keto-adaptation process. The duration of this process is individual and depends, among other things, on the metabolic fitness of the body. How can you verify if you are in ketosis? The symptoms of ketosis are individual, ambiguous and highly variable. This means that when you are in ketosis, you may only experience a fraction of them, and therefore it is quite difficult to unambiguously indicate whether the body has been put into a state of ketosis. Only the measurement of ketone bodies is authoritative. Nevertheless, it is worth observing your body’s reactions. This will make it easier to interpret the changes that have occurred in the keto-adaptation process and allow a reliable assessment of progress.

Ketosis – symptoms include:

  • dry mouth and increased thirst;
  • bad breath;
  • increased frequency of urination
  • decreased appetite;
  • digestive problems;
  • insomnia;
  • decreased exercise capacity;
  • weight loss;
  • short-term fatigue.

Ketosis: positive symptoms

Changing to a high-fat, low-carbohydrate and ketogenic lifestyle involves following strict rules, which is often very difficult. The effort pays off: following a ketogenic diet has a positive effect on health. Desirable aspects of ketosis include rapid and effective weight loss, improved brain function and mental performance, increased energy levels, reduction of inflammation and regulation of cholesterol levels. Completing the keto-adaptation process and entering a state of ketosis is also associated with normalisation of blood sugar levels, regulation of blood pressure improvement in complexion (especially for acne-prone skin), achievement of hormonal balance and improved mental health.

Ketosis: potential negative effects

Adherence to a ketogenic diet primarily results in a relatively rapid weight reduction, improved glycaemia and noticeably less frequent insulin secretions. According to opponents of ketosis, this is not enough to initiate keto-adaptation and fundamentally change the diet. Especially since they consider the ketogenic diet to be unnatural for humans. Additionally, the keto-diet is accused of being incompatible with current dietary recommendations, among other things, and the negative effects of ketosis are considered to include vitamin and micronutrient deficiencies and keto flu (gastrointestinal problems).

Ketosis: Potential risks and for whom might it be unhealthy?

Ketosis is a process during which the body starts to burn fat to produce energy instead of carbohydrates. Although it can be beneficial for some people, there are certain conditions and diseases for which entering a state of ketosis can be unhealthy. People with reactive hypoglycaemia, certain cases of insulin resistance, kidney and liver disease and some diabetic patients, especially those on sugar-lowering drugs, should be cautious and consult their doctor before starting a ketogenic diet. For children, ketosis is only used in specific clinical settings and always under medical supervision.

Ketosis and its effects on the body: from muscle mass to kidneys.

While ketosis can benefit fat loss, there are reports suggesting that it can also lead to loss of muscle mass. Protein, a key component of the diet, may be less effective at building muscle mass without the support of carbohydrates. Muscle weakness is also associated with potential joint weakness. Furthermore, an improperly balanced ketogenic diet can put the kidneys at risk, increasing the risk of kidney stones and gout. It is important to pay attention to the variety of foods consumed and avoid over-consumption of meat and animal proteins. Additionally, dehydration is a common side effect of entering ketosis, so adequate hydration and electrolyte replenishment are essential. Furthermore, restricting carbohydrate intake can lead to vitamin and mineral deficiencies, which can be particularly dangerous in the long term.

When does the body enter a state of ketosis?

Achieving a state of ketosis as a result of a ketogenic diet is a highly individualised process. The time it takes to undergo keto-adaptation and achieve ketosis depends, among other things, on the level of physical activity, BMI, age, metabolic fitness and stress levels. The diet prior to the introduction of the ketogenic diet also matters: if it was rich in carbohydrates, glucose stores are proportionally higher and it may take longer to reach ketosis.
It is worth knowing that ketosis does not only occur when following a ketogenic diet. The body enters ketosis, among other things, as a result of a long break between meals (e.g. in the morning, immediately after waking up) and after intensive exercise (post-exercise ketosis). The state thus achieved is maintained until carbohydrates are supplied to the body.

Exogenous ketones as an alternative way to a state of ketosis

Another way to bring the body into the desired state of ketosis is to supply the body with exogenous ketone bodies on its own. This is a common practice in sport as it improves endurance performance: supplements containing exogenous ketones induce a state of nutritional ketosis in just a few minutes. Carbohydrate restriction in the diet in this case is not necessary. [2]

Ketone bodies and the state of ketosis

Can putting the body into a state of ketosis be dangerous? In extreme cases, yes; however, this is especially the case for people struggling with diabetes. Increased production of ketone bodies up to a level of 25 mmol/L can lead to ketosis and ketoacidosis, but this is not achievable following a ketogenic diet by a healthy person. This is because during nutritional ketosis, the phenomenon of an increase in ketone bodies in the bloodstream is noticed when glucose and insulin levels are low and stable, which does not lead to a change in blood pH.

The level of ketone bodies in the blood is regulated by two processes: ketogenesis (production of ketone bodies) and ketolysis (degradation of ketone bodies). These are controlled by glucagon (which accelerates the production of ketones) and insulin, which slows down this production. [3]

State of ketosis versus the ketogenic diet

The aim of the ketogenic diet is to put the body into a state of ketosis. The dietary pattern appropriate to the keto-diet consists of increasing fat intake (of both plant and animal origin), while eliminating carbohydrates and limiting protein intake. The correct dietary pattern appropriate for the keto diet should contain around 90% fats. This is when the levels of ketone bodies can increase and the process of efficient fat burning can begin. Interestingly, from an energy point of view, ketone bodies provide more energy, hence, despite the caloric deficit, the decrease in energy is not felt (apart from the keto-adaptation process).

Keto-adaptation, or how do you get your body into ketosis?

The transition to a ketogenic diet, according to current knowledge, should be preceded by a keto-adaptation process. This is necessary for the body to learn to use the new energy sources (fatty acids and ketone bodies). Keto-adaptation involves a radical reduction in carbohydrates or giving them up altogether. Depending on the factors mentioned earlier, the duration of the process is highly individualised. However, it is assumed that it lasts approximately one month. After this time, the body functions in a state of ketosis.

When does keto-adaptation begin?

Keto-adaptation begins when carbohydrates are radically reduced or completely abandoned. This process involves strict recommendations regarding the distribution of macronutrients in the meals consumed and the need to strictly adhere to them. The recommended proportions in percentage terms are as follows:

  • fats – 80-85% of calories consumed;
  • proteins – 10-15% of calories consumed;
  • carbohydrates – 5% of calories consumed.

It is important to remember that during the keto-adaptation period, one should not be on a negative calorie balance: the very process of entering ketosis is a huge strain on the body. During this time, many people observe, among other things, a worsening of their mood (usually between days 2 and 5 of keto adaptation).

How to speed up the adaptation process?

Although keto adaptation is a highly individualised process and has no set duration, it can be safely accelerated. In order to prepare your body for the state of ketosis better and faster:

  • undertake regular physical activity;
  • drink significant amounts of water
  • replenish any deficiencies, especially sodium, potassium, calcium and magnesium supplements;
  • count calories, check the macronutrient content of your meals and avoid caloric deficits;
  • check the labels of the products you buy;
  • increase the amount of green vegetables in your diet;
  • use high quality supplements;
  • take care of recovery.

Ketosis – methods of measurement

Ketosis is a metabolic state in which the body begins to use fats as its main source of energy, leading to the production of ketone bodies in the liver. Their presence in the blood, breath or urine is a sign that the body is using fats instead of glucose. For many people, especially those on ketogenic diets, monitoring the state of ketosis is extremely important to ensure that the body functions properly and achieves the desired health or dietary outcomes. This is why the availability of different methods to measure ketone bodies is so valuable. Below we discuss the three main methods of monitoring ketone body levels.

Blood levels of ketone bodies

The most reliable method for determining the state of ketosis is to measure the concentration of ketone bodies (mainly beta-hydroxybutyrate) in the bloodstream. There are now many models of self-measuring devices for measuring ketone bodies, which resemble glucometers, available on the market. This involves pricking the finger with a lancet and applying a sample to a test strip. This method is quite expensive and requires an unpleasant pricking of the finger.

Breath ketone levels

An alternative to repeated pricking is to measure ketone bodies in the breath. It only requires blowing into a mouthpiece for a set period of time to obtain a result. Cheaper models of the device are not very precise and can determine the level of ketone bodies at levels of none, low or high. To get a more precise result, you need to invest a lot more in an analyser. The main problem with breath analysis is that it presents the content of acetone, which is not a major ketone body. Hence, the result can be falsified.

Ketone strips – levels of ketone bodies in urine

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


  1. Drabinska, 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.

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