Ketosis Symptoms: the Bridge Between Experience and Science

Ketosis Symptoms: the Bridge Between Experience and Science – Introduction

What is Ketosis

Ketosis is a state in which our blood contains an increased concentration of ketone bodies, namely acetone, acetoacetate, and beta-hydroxybutyrate.

Ketosis is a metabolic state characterized by elevated levels of ketone bodies in the body tissues, which can be induced by a ketogenic diet (nutritional ketosis) or fasting. While ketosis can be beneficial in the context of a controlled diet or fasting, uncontrolled ketosis in individuals with diabetes can lead to ketoacidosis, a potentially life-threatening condition.

For example, in people with diabetes mellitus or alcohol-related disorders, ketosis is a dangerous state, usually accompanied by other metabolic disarrangements that signal a failure from the body to properly adapt to a determined metabolic state. This usually occurs in the context of underlying infections or other health problems that destabilize the way the body deals with nutrients and energy.

On the contrary, nutritional ketosis is considered a physiological response to the diet, meaning a normal way to adapt to an environmental stimulus. While fasting and the early years of life may involve physiological ketosis, pregnancy is a condition where ketone levels might be carefully monitored, as excessive ketones can be concerning. Pregnant women should consult with healthcare providers before making significant dietary changes. In these scenarios, the concentration and ratio of ketone bodies are different from that of pathological causes of hyperketonemia. (1)

Ketosis Symptoms

Ketosis Symptoms: the Bridge Between Experience and Science

The Ketogenic Diet as a Way of Achieving Nutritional Ketosis

The ketogenic diet has been used since the 1920s to treat epilepsy, especially in children who do not respond to conventional seizure medications. Its application has been well-documented and continues to be a significant area of medical research and practice. At that time, antiseizure medications were not known, and many scientists found the high-fat, low-carbohydrate diet very useful for treating this life-diminishing disorder. (1)

Years have passed since then, and the ketogenic diet has continued to be explored for many other applications. Notably, the most studied one is its ability to improve weight in overweight people. Other applications under investigation include exercise performance, sleep, neurocognitive performance, cardiovascular health, diabetes management, and overall inflammatory control. (1-5)

Nowadays, the keto diet is probably one of the most popular dietetic approaches out there, with many people turning to this habit with the hope of improving their lives.

In this article, we are going to discuss the several symptoms that nutritional ketosis could produce in people and the relationship between these and the changes that the body experiences in nutritional ketosis.

Ketosis Symptoms in Nutritional Ketosis: What We Might Experience

Some Negative Ketosis Symptoms

It has been one or two days since one started this challenging dietetic regimen. Difficulties arise with frequencies and new food types since the classic Western diet is different from this new approach. Initially, a sense of lack of energy might arise, including decreased exercise tolerance. (6, 7)

The “keto flu” is a term used to describe a collection of symptoms including headache, fatigue, dizziness, nausea, and irritability that some people may experience when beginning a ketogenic diet. These symptoms are temporary and usually resolve within a week.

In other cases, people experience gastrointestinal issues, such as constipation, diarrhea, and abdominal bloating. Other less common manifestations include kidney stones, dehydration, and decreased bone density. Not every person experiences the same symptoms and with the same intensity or pattern, and not everyone has them. Fortunately, the adverse reactions of the ketogenic diet are transient and usually mild, lasting for a range of three to seven days. (1, 8)

Positive Ketosis Symptoms

Among the positive signs of doing keto, rapid weight loss is seen in the first few weeks, and most studies addressing this change found a significant weight loss in the first weeks in comparison to other dietetical approaches, whether or not the person is calory-restricted. The first quantity of weight loss is generally due to a greater water loss compared to a high carbohydrate diet. (1, 4)

An increase in urination can occur as the body sheds water weight and electrolytes during the initial stages of a ketogenic diet, necessitating increased fluid intake to prevent dehydration. This manifestation usually implies more intake of fluids.

A change in breath is commonly seen (9), which is fruity in odor and can represent discomfort to the person. This manifestation is characteristic of ketogenesis, the increased production of ketone bodies in the body.

With the days coming up, decreased appetite ensues, and people usually report a stable energy level and increased satiety with meals. (5)

At this time, there are several ways to test for the presence of hyperketonemia. The most accurate are blood tests, while urine and breath tests are less accurate but widely available to the general public. 

Why are Symptoms of Ketosis Produced

The Metabolic Switch

The keto diet produces a switch in the metabolic mechanisms that our bodies use to produce energy. Conventional diets usually consist of high amounts of carbohydrates (starch and sugars), which are transformed by the liver and muscle into glucose, a molecule that is easily transformed into energy.

When glucose is available, the whole body’s factory of energy is prepared to receive glucose to produce the energy for every other process going on. But when high fat and low carbohydrates are digested and processed, the cells do not receive the expected amount of glucose, and our liver starts producing it by way of its glycogen storages (a long chain of glucose molecules). As soon as glycogen runs out, hormonal signaling drives the usage of another substance as fuel: fat. (10)

The liver and muscles metabolize fat transported by the blood from our subcutaneous storages, producing energy from fatty acids at a lower cost process. As time under the diet goes on, the liver synthesizes a new molecule as a result of fat metabolism: ketone bodies. (11)

It Takes Some Days for the Body to Adapt

Progressively, almost the entire body is accustomed to using ketone bodies for energy production, with the exception of red blood cells and the proper liver cells, which rely on the energy produced by fats in the process of producing ketone bodies.

The metabolic switch takes some days to take over, and in the meantime, the body has to adapt to this new metabolic state. The symptoms of nutritional ketosis are mostly caused by the installment of this new mechanism at play. Imagine a factory that produces energy from the wind, but suddenly, they change to another natural source of energy, like a nearby river. The factory would have to change its machinery to process the new source of energy, and it would take some time.

In an analogous manner, the cells need to increase the machinery suitable for ketone body metabolism, and the system might struggle until the process is completed.

Ketosis Symptoms Frequently Asked Questions

How long does it take to get into ketosis?

The exact time is variable among people. The more time you are in ketosis, the easier it is to get into ketosis once again. It typically takes between 2 to 7 days to enter ketosis on a ketogenic diet, depending on various factors such as physical activity level, metabolism, age, carbohydrate intake, and fat intake.

What is the difference between nutritional ketosis and pathological ketosis?

Nutritional ketosis is a physiological process, that is, it is a normal state under certain conditions (for example, while on a ketogenic diet). On the contrary, pathological ketosis occurs when there is a metabolic imbalance in the body, such as that produced by uncontrolled diabetes or excessive alcohol consumption. Pathological ketosis is a life-threatening situation and requires medical attention.

How can you test your ketone levels?

Urinary ketone strips are a simple and cost-effective method to detect ketosis, but blood ketone meters provide a more accurate measurement of ketone levels. To use them you need to collect fresh urine iin a recipient and dip the reactive strip, as directed by the product instructions. A change of color will take place, indicating the level of ketones in the body, by referencing a table of colors.

What are the risks of nutritional ketosis?

While nutritional ketosis is generally safe for many people, it's important for individuals with specific health conditions, such as type 1 diabetes, pancreatitis, liver failure, or disorders of fat metabolism, to consult a healthcare professional before starting a ketogenic diet due to increased risks. As mentioned in the article, most people experience “the keto flu,” which usually takes a few days to one or two weeks to wane off.
Individuals with conditions such as Pyruvate carboxylase deficiency, Porphyria, and certain fat metabolism disorders should avoid a ketogenic diet due to the risk of exacerbating their condition and should only consider dietary changes under strict medical supervision. It is good advice to consult your doctor to check if you are a good fit for the keto diet.

What causes bad breath during ketosis?

One of the ketone bodies produced when you are in ketosis is acetone. This molecule has the capacity to travel to the lungs and aerosolize into your breath and has a particular smell. While chewing mint gum can temporarily mask the odor of acetone breath, increasing water intake and practicing good oral hygiene can also help minimize the odor.

Wrapping up

In conclusion, ketosis symptoms under physiologic nutritional-induced ketosis are a common manifestation of the body’s adaptation to a low-carbohydrate diet. It may take a few to several days for the symptoms to wane off, while the benefits of the keto diet progressively appear, manifesting as increased energy levels, weight loss, and improvement in sleep, cognition, and immunity. 

Ketosis symptoms are common and may differ from person to person, disappearing in a few days with minor repercussions. They probably pertain to the processes that underlie the metabolic shift until the body is completely adapted to the new diet.

A ketogenic diet, as well as any other health intervention, should be followed with the guidance of specialized health professionals in order to understand if the diet is the correct approach for you and to have the best results possible.

See Also

Ketogenic Diet and Constipation

Atkins Ketogenic Diet Plan

Is Quinoa Keto Friendly?

Are Carrots Keto?

Is Milk Keto?

Is Honey Keto Friendly?

Keto Diet for Women Over 50

Dirty Keto Food List

Keto Diet for Beginners

Current Version
April 17, 2023
Written By
Franco Cuevas, MD

1. Masood W, Annamaraju P, Uppaluri KR. Ketogenic diet. InStatPearls [Internet] 2021 Nov 26. StatPearls Publishing. Ketogenic Diet – StatPearls – NCBI Bookshelf (

2. Hirschberger S, Strauß G, Effinger D, Marstaller X, Ferstl A, Müller MB, Wu T, Hübner M, Rahmel T, Mascolo H, Exner N. Very‐low‐carbohydrate diet enhances human T‐cell immunity through immunometabolic reprogramming. EMBO Molecular Medicine. 2021 Aug 9;13(8):e14323. Very‐low‐carbohydrate diet enhances human T‐cell immunity through immunometabolic reprogramming | EMBO Molecular Medicine (

3. Krikorian R, Shidler MD, Dangelo K, Couch SC, Benoit SC, Clegg DJ. Dietary ketosis enhances memory in mild cognitive impairment. Neurobiology of aging. 2012 Feb 1;33(2):425-e19. Dietary ketosis enhances memory in mild cognitive impairment – PubMed (

4. Yancy Jr WS, 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. Annals of internal medicine. 2004 May 18;140(10):769-77. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: a randomized, controlled trial – PubMed (

5. Cohen CW, Fontaine KR, Arend RC, Soleymani T, Gower BA. Favorable effects of a ketogenic diet on physical function, perceived energy, and food cravings in women with ovarian or endometrial cancer: a randomized, controlled trial. Nutrients. 2018 Aug 30;10(9):1187.  Favorable Effects of a Ketogenic Diet on Physical Function, Perceived Energy, and Food Cravings in Women with Ovarian or Endometrial Cancer: A Randomized, Controlled Trial – PubMed (

6. Urbain P, Strom L, Morawski L, Wehrle A, Deibert P, Bertz H. Impact of a 6-week non-energy-restricted ketogenic diet on physical fitness, body composition and biochemical parameters in healthy adults. Nutrition & metabolism. 2017 Dec;14(1):1-1. Impact of a 6-week non-energy-restricted ketogenic diet on physical fitness, body composition and biochemical parameters in healthy adults | Nutrition & Metabolism | Full Text (

7. Sjödin A, Hellström F, Sehlstedt E, Svensson M, Burén J. Effects of a ketogenic diet on muscle fatigue in healthy, young, normal-weight women: a randomized controlled feeding trial. Nutrients. 2020 Mar 30;12(4):955. Effects of a Ketogenic Diet on Muscle Fatigue in Healthy, Young, Normal-Weight Women: A Randomized Controlled Feeding Trial – PubMed (

8. Shalabi H, Alotaibi A, Alqahtani A, Alattas H, Alghamdi Z, Alattas Sr HK, Alghamdi Sr Z. Ketogenic diets: side effects, attitude, and quality of life. Cureus. 2021 Dec 13;13(12). Ketogenic Diets: Side Effects, At… preview & related info | Mendeley

9. Alkedeh O, Priefer R. The ketogenic diet: breath acetone sensing technology. Biosensors. 2021 Jan 19;11(1):26. The Ketogenic Diet: Breath Acetone Sensing Technology – PubMed (

10. Laffel L. Ketone bodies: a review of physiology, pathophysiology and application of monitoring to diabetes. Diabetes/metabolism research and reviews. 1999 Nov 1;15(6):412-26. Ketone bodies: a review of physiology, pathophysiology and application of monitoring to diabetes – PubMed (

11. Leonard TG. The physiology of ketosis and the ketogenic diet. Southern African Journal of Anaesthesia and Analgesia. 2020 Nov 13;26(6):S94-97. [PDF] The physiology of ketosis and the ketogenic diet | Semantic Scholar