How Long Does It Take to Get into Ketosis?

One burning question often lingers in the minds of individuals embarking on their dietary journey: how long does it take to get into ketosis?

In this comprehensive guide, we will discuss the science behind ketosis initiation, explore the factors that influence the time it takes, and offer insights into recognizing the signs of successful ketosis.

Key Takeaways:

  • 24 hours of water fasting put you into ketosis.
  • Approximately a week of a ketogenic diet puts you into ketosis.
  • The time heavily depends on individual factors like metabolism and age.

Table of Contents:

How Long Does It Take to Get into Ketosis?

Entering ketosis takes 24 hours of fasting or several days to weeks following a keto diet.

But this timeframe is not universal. Mild ketosis generally develops in 12-14 hours of fasting.1

The duration varies among individuals due to many factors influencing the body’s metabolic response. According to a review of several studies, the mean time for ketosis is 33 hours (range 17 to 48), and for good ketosis, 58 hours (range 40 to 84).2

These studies also consider the urinary ketone results as an indicator of “good ketosis,” where the body is burning enough fats for ketones to appear in the urine.

Moreover, these ranges do not apply to people with diabetes, as they metabolize sugar and fats differently.

Why Do Some People Take Longer to Enter Ketosis?

how long does it take to get into ketosis


Your metabolic rate heavily influences the speed at which your body enters ketosis. Individuals with a faster metabolism often transition into ketosis more quickly.

Regular exercise and maintaining muscle mass can contribute to an efficient metabolism, expediting the process.

Carbohydrate Intake

Restricting carbohydrate intake is fundamental to kickstarting ketosis. Those who rigorously adhere to a low-carb or ketogenic diet are likely to enter ketosis sooner.

While most take up to 50 grams of carbohydrates daily, some also take as little as 15 grams to enter ketosis quickly.

Fat Consumption

The relationship between fat intake and ketosis is pivotal. A diet rich in healthy fats promotes ketosis, as the body learns to burn fat for fuel. Adopting a high-fat diet facilitates fat adaptation, a process that aids in quickly initiating ketosis.

Avocado and avocado oil, wild-caught fish, cheese, yogurt, and olive oil are good sources of healthy fats that you should incorporate into your meal plan.

Protein Intake

Experts recommend taking less than 1 gram of protein for every pound of body weight when aiming for ketosis. Striking the right balance with protein is key when it comes to ketosis.

While protein is a necessary component of any diet, excessive intake can impede the onset of ketosis. If you take too much protein, your body will burn the amino acids first and hinder ketosis from occurring.

Physical Activity

Physical activity accelerates glycogen depletion, aiding in the initiation of ketosis. Regular exercise, especially high-intensity workouts, can expedite the transition.3

Moreover, fitness levels and the type of exercise performed influence the rate at which the body exhausts its glycogen stores.


Metabolism tends to slow down with age, impacting the rate at which the body enters ketosis. Older individuals may experience a more gradual transition. The study that reported ketosis after 17 hours2 was conducted on younger individuals.

Younger individuals may adapt more quickly to dietary changes, potentially leading to a faster onset of ketosis, especially when you’re only trying the ketogenic diet for the first time.


Individuals practicing intermittent fasting may enter ketosis more rapidly during fasting periods. Fasting accelerates the depletion of glycogen stores, pushing the body into ketosis.

However, if you are capable of doing both the keto diet and intermittent fasting at the same time, you will more likely go into ketosis faster.

Body Composition

Individuals with higher body fat percentages often have more stored energy in the form of fat. This can facilitate a quicker transition to ketosis as the body has readily available fat stores to utilize.

Lack of Sleep

Inadequate sleep can disrupt hormonal balance, including decreased insulin sensitivity.4 Poor sleep quality may slow the body’s ability to utilize stored glycogen and enter ketosis efficiently.


Stress triggers the release of cortisol,5 a hormone that can increase blood sugar levels. Elevated cortisol levels may hinder the transition to ketosis by maintaining glucose availability.

Stress management techniques, such as meditation or yoga, can positively impact the speed of ketosis and increase fasting tolerance.

How to Know You Are in Ketosis

The best way to know if you are in ketosis is to test for ketone levels in blood, breath, or urine.

Symptoms vary per individual, and you may or may not experience the common symptoms associated with ketosis.

Increased Ketone Levels

One of the most direct ways to confirm ketosis is by measuring ketone levels.

  • Ketones in Blood: Blood ketone levels typically rise during ketosis. A reading above 0.5 mmol/L is considered indicative of ketosis.
  • Acetone in Breath: Elevated acetone levels contribute to a distinct breath odor. While unpleasant, it’s a reliable sign that your body produces ketones.
  • Ketones in Urine: Urine test strips can also indicate ketosis.

Adaptation Period Symptoms

Some individuals experience symptoms resembling the flu during the initial stages of ketosis. This includes fatigue, headaches, nausea, and dizziness. These symptoms,6 collectively known as keto flu, are transient and indicate the body’s adjustment to a low-carb state.

Keto flu symptoms typically subside within a few days to a week as the body adapts to using ketones for energy.

Enhanced Mental Clarity and Focus

Many individuals report heightened mental clarity and focus when in ketosis. The brain efficiently utilizes ketones, providing a stable energy source and reducing the cognitive fog associated with carb-heavy diets.

Appetite Suppression

Ketosis is often associated with reduced feelings of hunger. This is attributed to stabilized blood sugar levels and the satiating effect of a high-fat diet.

Tips to Get into Ketosis Fast

Limiting carbohydrate intake and regular exercise are the best ways to get into ketosis fast. If you’re not reaching your desired goals even when doing a keto diet or fasting, try incorporating these tips:

  • Strict Low-Carb Diet: Start by significantly reducing your carbohydrate intake. Prioritize non-starchy vegetables and low-carb fruits to meet your fiber and micronutrient needs without compromising ketosis.
  • Engage in Cardio and Resistance Training: Aerobic and resistance exercises deplete glycogen stores, promoting a quicker transition into ketosis. Aim for a combination of cardiovascular and strength-training workouts.
  • Embrace Healthy Fats: Incorporate healthy fats into your diet, including avocados, olive oil, coconut oil, and fatty fish.
  • Consider Fasting Time: For those comfortable with longer fasting periods, extended fasts (24-48 hours) can expedite the depletion of glycogen stores.
  • MCT Oil Benefits: Medium-chain triglycerides (MCTs)7 are easily converted into ketones. Add MCT oil slowly into your diet to coffee, smoothies, or salad dressings.
  • Maintain a Holistic Lifestyle: Stay hydrated, avoid stress, and get adequate sleep for better results.

When Does Ketosis Start When Water Fasting

Water fasting for 24 hours puts your body in ketosis.

Like any form of fasting, the time it takes to initiate ketosis in water fasting differs per individual but could start as early as 16 hours.

Within the first 24 hours of water fasting, glycogen stores are rapidly depleted. This depletion reduces water weight, often noticed as an initial drop on the scale.

As glycogen depletes, the body uses alternative fuel sources, namely ketones derived from fat breakdown. This shift marks the initiation of ketosis.

Frequently Asked Questions

What are the first signs of ketosis?

The initial signs of ketosis often include increased ketone levels, a distinct breath odor, and improved mental focus.

When will I know I’m in ketosis?

Ketosis can be confirmed by monitoring ketone levels through blood, breath, or urine tests. The presence of ketones indicates a successful transition.

How quickly can you get into ketosis?

This depends on how fast your body burns fats. Scientific studies have reported ketosis as early as 17 hours and as late as 48 hours.

Will a 16-hour fast put me in ketosis?

Yes, a 16-hour fast may put you in ketosis. Some studies suggest that short-term fasting, as in intermittent fasting or alternate-day fasting, shows better results than long-term fasting.


1Ghimire, P., & Dhamoon, A. S. (2023). Ketoacidosis. In StatPearls. StatPearls Publishing.

2Wirrell, E. C., Darwish, H. Z., Williams-Dyjur, C., Blackman, M., & Lange, V. (2002). Is a fast necessary when initiating the ketogenic diet?. Journal of child neurology, 17(3), 179–182.

3Lee HS, Lee J. Effects of Combined Exercise and Low Carbohydrate Ketogenic Diet Interventions on Waist Circumference and Triglycerides in Overweight and Obese Individuals: A Systematic Review and Meta-Analysis. Int J Environ Res Public Health. 2021 Jan 19;18(2):828. doi: 10.3390/ijerph18020828. PMID: 33478022; PMCID: PMC7835865.

4Mesarwi O, Polak J, Jun J, Polotsky VY. Sleep disorders and the development of insulin resistance and obesity. Endocrinol Metab Clin North Am. 2013 Sep;42(3):617-34. doi: 10.1016/j.ecl.2013.05.001. PMID: 24011890; PMCID: PMC3767932.

5Cay M, Ucar C, Senol D, Cevirgen F, Ozbag D, Altay Z, Yildiz S. Effect of increase in cortisol level due to stress in healthy young individuals on dynamic and static balance scores. North Clin Istanb. 2018 May 29;5(4):295-301. doi: 10.14744/nci.2017.42103. PMID: 30859159; PMCID: PMC6371989.

6Batch JT, Lamsal SP, Adkins M, Sultan S, Ramirez MN. Advantages and Disadvantages of the Ketogenic Diet: A Review Article. Cureus. 2020 Aug 10;12(8):e9639. doi: 10.7759/cureus.9639. PMID: 32923239; PMCID: PMC7480775.

7Lin TY, Liu HW, Hung TM. The Ketogenic Effect of Medium-Chain Triacylglycerides. Front Nutr. 2021 Nov 18;8:747284. doi: 10.3389/fnut.2021.747284. PMID: 34888335; PMCID: PMC8650700.

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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