Ketosis: Definition, Symptoms, Benefits, and Side Effects

Ketosis, the main aim of the ketogenic diet, is the process of switching the energy source from glucose to fat.

For this reason, the ketogenic diet is currently one of the most popular diets. You’re on the right page if you want an in-depth discussion on ketosis.

This comprehensive article will discuss everything you need to know about ketosis, its symptoms, benefits, and side effects.

Key Takeaways:

  • Ketosis means you burn fat instead of glucose for energy.
  • A low-carb, high-fat diet, such as keto, can induce the metabolic state.
  • You can get into ketosis in a week when you stay under 50 g of carbs per day.

Table of Contents:

What Is Ketosis?

Ketosis is a metabolic state where you burn fat instead of glucose for energy.

It is characterized by elevated levels of ketone bodies in the bloodstream.

This state is a natural physiological response to reduced carbohydrate intake, typically associated with fasting, a low-carbohydrate diet, or prolonged physical exertion.

Biochemical Foundations of Ketosis

  1. Carbohydrate Depletion: Carbohydrates are the body’s preferred energy source and are broken down into glucose for fuel. When carbohydrates are scarce, as in a low-carb diet or during fasting, the body turns to alternative sources, primarily ketone bodies.
  2. Glycogen Stores Exhaustion: The body stores excess glucose in the form of glycogen, primarily in the liver and muscles. The glycogen stores decrease along with carbohydrates. This depletion initiates a cascade of hormonal changes, including reduced insulin production.
  3. Insulin’s Role: Insulin, a hormone produced by the pancreas, plays a central role in glucose metabolism. When insulin levels drop, the body transitions from utilizing glucose to breaking down stored fat for energy. This reduction in insulin promotes the release of fatty acids from fat cells.
  4. Fatty Acid Oxidation: Fatty acids released from fat cells enter the liver, where they undergo a process called beta-oxidation. This process breaks down fatty acids into molecules known as ketone bodies. The primary ketones produced are acetoacetate, beta-hydroxybutyrate, and acetone.
  5. Ketone Utilization: Ketones become the alternative fuel source in the absence of glucose. They can cross the blood-brain barrier, providing energy to the brain, muscles, and other tissues. This transition to ketone metabolism marks the onset of ketosis.

Ketosis and the Keto Diet

The ketogenic diet, often referred to as the keto diet, is a low-carbohydrate, high-fat eating approach designed to induce and maintain a state of ketosis in the body.

By limiting carb intake and increasing the consumption of healthy fats, individuals aim to promote fat metabolism and reap the benefits associated with ketosis.

The ketogenic diet was first introduced as a treatment modality for epilepsy, aiming to burn more fats than carbs, as ketone bodies have an epileptic effect on the brain.1 Up to this day, the keto diet remains one of the most popular approaches to reducing body fats.

Ketosis is induced by eating butter and salmon

Dietary Composition: Key Components of the Keto Diet

  1. High Healthy Fats: A hallmark of the keto diet is its emphasis on healthy fats. Avocado, olive oil, nuts, and fatty fish contribute to most daily caloric intake.
  2. Moderate Protein: Protein intake should be moderate and varies based on individual factors such as activity level and muscle mass. Sources include meat, poultry, fish, eggs, and dairy. The classic ketogenic diet requires one gram of protein per kilogram of body weight.
  3. Low Carbohydrates: The distinguishing feature of the keto diet is its restriction of carbohydrates. Carbohydrate intake is typically limited to 20-50 grams per day, which forces the body to transition from glucose to ketone bodies as the primary fuel source.

How many carbs do I need for ketosis?

The general guideline2 is to limit daily carbohydrate intake from 10-50 grams to achieve ketosis. The macronutrient distribution typically ranges from approximately 55% to 60% fat, 30% to 35% protein, and only about 5% to 10% carbohydrates.

However, the carbohydrate threshold for entering ketosis is not one-size-fits-all. Factors such as metabolism, activity level, and insulin sensitivity influence the amount of carbohydrates an individual can consume while staying in ketosis.

Most individuals follow the concept of net carbs, which subtracts fiber content from total carbohydrate intake. Fiber does not significantly impact blood sugar and insulin levels, making it a preferred source of carbohydrates for those in ketosis.

How long does it take to get into ketosis?

You can achieve ketosis by fasting for longer than 72 hours or by following a very ketogenic diet for several days to weeks.3

However, the timeline for entering ketosis varies from person to person and depends on several factors, including dietary habits, physical activity, and individual metabolism.

Using ketone testing methods, individuals can track their progress and determine when they officially enter ketosis. Blood tests provide the most accurate and real-time assessment.

Health Benefits of Ketosis

Weight Loss

One of the primary reasons people follow a ketogenic diet is for weight loss, especially among obese4 and people with diabetes.5 When the body is in ketosis, it becomes more efficient at burning stored fat for energy. Additionally, ketones have been shown to have appetite-suppressing effects,6  leading to reduced calorie intake.

Stable Blood Sugar Levels

Ketogenic diets may help stabilize blood sugar levels7 by reducing the consumption of high-glycemic carbohydrates. This can be particularly beneficial for individuals with type 2 diabetes or insulin resistance. In most studies, the decrease in sugar levels also means decreased body weight.

Increased Energy and Mental Clarity

Many people report increased energy levels and improved mental clarity8 when in ketosis. The brain can efficiently use ketones as an alternative fuel source, enhancing cognitive function for some individuals.

Anti-inflammatory and Neuroprotective Effects

Experts link chronic inflammation to various health issues, including heart disease and autoimmune disorders. Ketones have been studied for their potential anti-inflammatory and neuroprotective effects. Some research suggests that ketosis may be beneficial for specific neurological conditions, such as epilepsy1 and Alzheimer’s disease.9

Appetite Regulation

Ketosis can lead to changes in hunger hormones, helping individuals regulate their appetite more effectively.10 Many people on ketogenic diets report feeling satisfied with smaller portions than those just cutting on carbohydrate intake.

Potential Cancer Benefits

While research is in the early stages, some studies suggest that ketosis may have numerous benefits for people with cancer. A comprehensive review states11 that ketogenic diets are well-tolerated by patients and help enhance the effects of antitumor therapies and increase their overall quality of life.

Ketosis Symptoms: Short-Term Side Effects of Ketosis

Before diving into this section, note that not everyone experiences these, and individuals may experience other symptoms not listed below. For safety purposes, always consult your healthcare provider for questionable symptoms.

Low Energy Levels

As the body transitions from relying on carbohydrates to fats for energy, some individuals experience a temporary dip in energy levels.

This phase, often termed the keto flu, is a transient adjustment period.12

Mild fatigue is also a typical response as the body learns to use stored fats efficiently as its primary energy source. These symptoms peak in the first week and diminish after 4 weeks.

Increased Urination

The reduction in glycogen stores leads to a decrease in water retention.

Consequently, the body sheds excess water through increased urination, contributing to an initial drop in weight.

Adequate hydration becomes crucial to counteract potential dehydration. While rare, renal issues may also arise,13 so check your renal function when doing the keto diet.

Distinct Breath Odor

A unique ketosis symptom is the development of what is commonly known as keto breath.

This occurs due to the presence of acetone, one of the ketone bodies, expelled through breath. People often describe the smell as slightly fruity or reminiscent of nail polish remover.

Electrolyte Imbalance and Muscle Cramps

With increased urination, there’s a risk of electrolyte imbalance. Sodium, magnesium, and potassium may be flushed out, potentially leading to symptoms like muscle cramps.14

Possible Digestive Issues

While studies show mixed results15 on this side effect, some individuals may experience digestive changes during the initial stages of ketosis.

This can include constipation or diarrhea as the gut adapts to the altered dietary composition. The shift in dietary patterns on a ketogenic diet may influence the gut microbiome. However, this could contribute to improvements in gut health over time.

Ketosis vs. Diabetic Ketoacidosis

The main difference between ketosis and ketoacidosis is the lack of control with ketoacidosis.

Ketosis, a natural and controlled process, occurs when the body utilizes ketones, derived from fat breakdown, as a primary energy source.

On the other hand, diabetic ketoacidosis is a severe complication primarily linked to uncontrolled diabetes, either type 1 or poorly managed type 2.

In DKA, there is an alarming increase in blood glucose levels, coupled with the accumulation of ketones, leading to a highly acidic environment in the body. This condition demands immediate medical attention due to its life-threatening nature.

Key differentiators include blood glucose levels and the nature of ketone accumulation.

In ketosis, blood glucose remains within a normal range, while in DKA, it skyrockets. Additionally, ketone levels, while elevated in both states, are under control in ketosis, whereas DKA represents an uncontrolled, pathological elevation.

How to Test for Ketosis

Monitoring the body’s transition into ketosis is a valuable aspect for those following a ketogenic diet or engaging in fasting.

Several methods offer insights into ketone levels, providing individuals a clear understanding of their metabolic state. Here are the primary ways to test for ketosis:

Urinary Ketone Strips:

  • Principle: These strips detect the presence of acetoacetate, a ketone excreted in urine.
  • Considerations: While cost-effective, this method may not be as accurate for those who have been in ketosis for an extended period, as the body becomes more efficient at utilizing ketones.

Blood Ketone Meters:

  • Principle: This method measures beta-hydroxybutyrate, the most abundant ketone in the blood.
  • Considerations: Blood ketone meters provide real-time and accurate ketone levels, making them a preferred choice for precise monitoring.

Breath Ketone Meters:

  • Principle: These devices measure acetone, a ketone released in the breath.
  • Considerations: While less invasive than blood testing, breath ketone meters may have variability in accuracy.

Exogenous Ketones

Exogenous ketones, often in the form of beta-hydroxybutyrate (BHB), are supplements designed to elevate blood ketone levels without requiring strict dietary adherence. These ketones aim to mimic the state of ketosis, providing a readily available energy source and mental clarity.

While they can be a quick fix for those seeking immediate benefits, it’s essential to recognize that reliance on exogenous ketones might hinder the body’s natural adaptation to producing ketones through dietary carbohydrate restriction. Users should view them as a temporary solution rather than a long-term strategy for sustaining ketosis.

Ketosis Pills and Drinks

Ketosis pills and drinks typically feature a blend of ingredients like exogenous ketones, MCT oil, and electrolytes, aiming to facilitate the transition into ketosis and mitigate potential side effects.

Both pills and drinks serve as supplementary tools for those seeking to optimize their ketogenic experience, and the choice between them hinges on individual preferences, lifestyle, and the desired method of consumption.

While keto pills and drinks are often well-tolerated by healthy individuals, it’s advisable to select products from reputable sources, ensure transparency in ingredient composition, and consult healthcare professionals for personalized advice when incorporating these supplements into a ketogenic regimen.

The Bottom Line

The process of entering ketosis varies among individuals, with factors like carb intake and metabolic health playing crucial roles. When experiencing ketosis, individuals may encounter symptoms and side effects, emphasizing the importance of a gradual transition and proper hydration.

While ketosis and keto diet boasts numerous scientific data to back its benefits and claims, a holistic approach is critical to achieving the best results. As usual, consult your healthcare professionals for any changes in your diet.

Frequently Asked Questions (FAQ)

How do I know I am in ketosis?

The most accurate way is to do testing. Methods such as urine strips, blood tests, and breath analyzers can confirm the presence of ketones in the body, indicating that you are in ketosis.

Is it good for your body to be in ketosis?

When approached responsibly, ketosis can be a healthy metabolic state associated with cognitive benefits, weight loss, and improved overall well-being.

How long is it safe to be in ketosis?

According to studies, it is safe to stay in ketosis or keep a keto diet for as long as 6-12 months. However, it is essential to closely monitor your diet and organ functions when staying in keto for long periods.

Why do ketones help you lose weight?

Ketones promote fat metabolism, reduce appetite, and increase energy expenditure, contributing to weight loss on a ketogenic diet.


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2Ashtary-Larky, D., Bagheri, R., Bavi, H., Baker, J. S., Moro, T., Mancin, L., & Paoli, A. (2022). Ketogenic diets, physical activity and body composition: A review. The British Journal of Nutrition, 127(12), 1898-1920.

3Scott, J. M., & Deuster, P. A. (2017). Ketones and Human Performance. Journal of special operations medicine : a peer reviewed journal for SOF medical professionals, 17(2), 112–116.

4Markovikj, G., Knights, V., & Kljusurić, J. G. (2023). Ketogenic Diet Applied in Weight Reduction of Overweight and Obese Individuals with Progress Prediction by Use of the Modified Wishnofsky Equation. Nutrients, 15(4).

5Zhou, C., Wang, M., Liang, J., He, G., & Chen, N. (2022). Ketogenic Diet Benefits to Weight Loss, Glycemic Control, and Lipid Profiles in Overweight Patients with Type 2 Diabetes Mellitus: A Meta-Analysis of Randomized Controlled Trails. International Journal of Environmental Research and Public Health, 19(16).

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9Pinto, A., Bonucci, A., Maggi, E., Corsi, M., & Businaro, R. (2018). Anti-Oxidant and Anti-Inflammatory Activity of Ketogenic Diet: New Perspectives for Neuroprotection in Alzheimer’s Disease. Antioxidants, 7(5).

10Gibson, A. A., Seimon, R. V., Lee, C. M., Ayre, J., Franklin, J., Markovic, T. P., Caterson, I. D., & Sainsbury, A. (2015). Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obesity reviews : an official journal of the International Association for the Study of Obesity, 16(1), 64–76.

11Weber, D. D., Aminzadeh-Gohari, S., Tulipan, J., Catalano, L., Feichtinger, R. G., & Kofler, B. (2020). Ketogenic diet in the treatment of cancer – Where do we stand? Molecular Metabolism, 33, 102-121.

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14Sjödin, A., Hellström, F., Sehlstedt, E., Svensson, M., & Burén, J. (2020). Effects of a Ketogenic Diet on Muscle Fatigue in Healthy, Young, Normal-Weight Women: A Randomized Controlled Feeding Trial. Nutrients, 12(4).

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Mag. Stephan Lederer, MSc.

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

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