How Long Does It Take To Enter Ketosis? - Healthline

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Evidence BasedHow Long Does It Take to Enter Ketosis?

Medically reviewed by Jared Meacham, PhD., RD, CSCS — Written by Ryan Raman, MS, RD — Updated on August 7, 2025

Timing
Signs
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Tips
Takeaway

If you’re starting the keto diet, it may take time to get into a ketotic state, which occurs when your body burns fat for fuel rather than carbs. Typically, it takes 2–4 days for your body to enter ketosis.

The goal of ketogenic diets is nutritional ketosis, which is achieved by restricting carbohydrate intake, moderating protein consumption, and increasing calories obtained from fat.

Restricting the body’s carbohydrate intake and increasing calories from fat helps your body switch its primary fuel source from glucose, a type of sugar, to ketones, or compounds made by breaking down fat that serve as an alternative fuel source.

The result is a metabolic state where the body prefers fat as its primary fuel source.

The time it takes to enter ketosis, or the metabolic state associated with your body using ketone bodies for fuel, can vary from person to person. Many individuals have difficulties entering ketosis in the first place.

This article explains how long it takes to enter ketosis and why you may not be there — yet.

How long does it take to enter ketosis?

To reap the benefits of a ketogenic diet, your body must enter a state called ketosis. This is a metabolic state in which your body converts fat into molecules called ketones, which it uses as its main energy source when glucose, a type of sugar, is limited.

The best way to reach ketosis is to reduce your intake of carbs drastically.

In your digestive tract, carbs are broken down into sugar molecules, such as glucose, so they can travel across the bloodstream and be used for energy. If your body has excess glucose, it can be stored in your liver and muscles in its storage form, glycogen.

By drastically reducing your carb intake to under 50 grams per day, your body is forced to use up its glycogen stores for energy — and eventually switch to using ketones as fuel.

The time it takes to enter ketosis varies from person to person. In general, it can take 2–4 days if you eat 20–50 grams of carbs per day. However, some people may find reaching this state takes a week or longer.

For example, people who typically consume a high carb diet before starting a keto diet may take longer to enter ketosis than those who generally eat a low to moderate-carb diet. This is because your body needs to deplete its glycogen stores before entering ketosis.

How to tell whether you’re in ketosis

As your body transitions into ketosis, you may experience several symptoms, sometimes known as the “keto flu.” These include headaches, fatigue, nausea, bad breath, and increased thirst.

While these symptoms may give you an indication that your body is transitioning, the best way to tell whether you’re in ketosis is to test your body’s ketone levels.

Ways to measure ketone levels

Testing your body’s ketone levels is the best way to know whether you’re in ketosis. There are three types of ketones — acetoacetate, acetone, and beta-hydroxybutyrate — that you can measure through your urine, breath, and blood, respectively.

Acetoacetate levels can be measured through your urine with a ketone urine strip, which turns various shades of pink or purple depending on the ketone level of your urine. Darker colors typically mean that your urine contains higher levels.

Urine testing strips are a cheap and simple way to tell whether you’re in ketosis. However, they may not be as accurate as other tools.

Acetone levels can be measured with a ketone breath meter, such as a Ketonix. This meter flashes a color to let you know whether you’re in ketosis and how high your ketone levels are. Studies show that ketone breath meters are fairly accurate.

Beta-hydroxybutyrate levels are measured using a blood ketone meter, which works similarly to a glucometer — a tool that measures blood glucose levels at home.

To use a blood ketone meter, simply use the small accompanying pin to prick your finger and draw blood, then let the top of the strip come in contact with your blood.

A blood ketone range of 0.5 to 3 mg/dL is ideal for maintaining ketosis.

While blood ketone meters are effective at measuring ketones, the strips — in contrast to urine testing strips — can be expensive.

Tools that measure ketone levels should give you an accurate idea of whether you’re in ketosis. This lets you know whether you need to make adjustments to enter or stay in this state.

Why do some people take longer to enter ketosis?

There are many reasons why some people take longer to enter ketosis than others. Multiple factors, including your age, metabolism, exercise level, and current carb, protein, and fat intake, can play a part in how long it takes to enter ketosis.

In most cases, taking longer to enter ketosis is due to unintentionally eating more carbs than recommended for a ketogenic diet. Eating too many carbs can stop your body from producing ketones. Therefore, you may need to further reduce your carb intake if you’re finding it difficult to enter ketosis.

Another common mistake is not eating enough fat on a ketogenic diet. In general, people should aim to consume about 55% to 60% of their daily calories from fat, 30% to 35% from protein, and 5% to 10% from carbs.

Also, eating too much protein on a keto diet may make it harder to enter ketosis, as it may encourage your body to use gluconeogenesis. This process converts amino acids from protein into sugar. Too much sugar can stop your body from producing ketones.

Aside from diet, lifestyle factors — including exercise, sleep, and stress — may affect the time it takes to enter ketosis.

If you’re having challenges getting into ketosis, check whether you’re experiencing any of the issues above.

What should you know before ‘going keto’?

‘Going keto’ is a popular way to lose weight, but there are certain risks and downsides associated with the diet that should be taken into consideration before trying it yourself.

While people on a ketogenic diet typically experience rapid weight loss initially — up to 10 pounds in 2 weeks or less — this may be due to the diet’s diuretic effect, meaning that some — but not all — weight loss is simply due to water loss.

Although low carb diets are associated with decreased sugar intake, which can lower an individual’s risk for obesity, diabetes, and other metabolic disorders, various concerns remain. One concern is that the long-term health implications of the keto diet are unknown.

Can you follow a keto diet if you’re a vegetarian or vegan?

If you’re a vegetarian or vegan and wondering if you can still do a keto diet, the answer is: Yes! It can be challenging at times, but it can be done.

Read more about how to follow a vegetarian keto diet and a vegan keto diet.

Long-term health complications of the keto diet

Potential long-term side effects may include fat buildup within the liver, kidney stones, inadequate protein levels, and vitamin deficiency, though these effects have not been consistently confirmed. More research is required to fully understand the consequences.

Another challenge associated with the keto diet is the decreased consumption of fruits and vegetables and increased fat consumption. Long-term low carb diets with increased fat consumption may cause inflammation and oxidative stress, and may even expedite aging.

Additionally, due to its strict limits, adhering to the keto diet can be challenging and even unsustainable for many people.

Individuals living with diabetes and taking insulin or oral hypoglycemic agents may experience severe hypoglycemia if medications are not appropriately adjusted before initiating this diet. Individuals who have pancreas or liver conditions, or metabolic disorders should also talk with their doctor before attempting this diet.

If you’re curious about ketosis, ask your doctor if the keto diet might be right for you.

Tips to achieve ketosis

If you struggle to get into ketosis, here are a few tips that can help you get there:

Eat 20–50 grams of carbs per day: This can encourage your body to produce ketones. People who have trouble entering ketosis may need to stick to the lower end of the scale.
Track your carb intake: This can help ensure you’re eating 20–50 grams of carbs per day and not underestimating your carb intake.
Limit eating out at restaurants: While there are many keto-friendly restaurants, eating out can make it harder to track your carbs.
Be aware of hidden carb sources: It’s easy to overlook condiment ingredients, but many sauces and dressings are high in carbs.
Increase your intake of high quality fats: Aim to get at least 55–60% of your calories from healthy fats, such as nuts, nut butter, extra virgin olive oil, avocado oil, avocados, meats, eggs, and fatty fish like salmon.
Try intermittent fasting: Fasts like intermittent fasting may help your body shift its fuel source from carbs to fat while maintaining its energy balance.
Exercise more: Physical activity can deplete your body’s glycogen stores, which encourages your liver to increase its production of ketones. Studies show that working out in a fasted state can help boost ketone levels.
Test your ketone levels regularly. Testing ketone levels can help give you an idea of whether you’re in ketosis, allowing you to adjust your diet accordingly.

Takeaway

The keto diet is not for everyone, but it may help with short-term weight loss goals.

In general, it should take you 2–4 days to enter ketosis. However, some people may find they need a week or longer. The time it takes depends on various factors, such as your age, metabolism, exercise level, and current carb, protein, and fat intake.

The best way to tell whether you’re in ketosis is to measure your ketone levels using either a breath, urine, or blood ketone measuring tool.

If you’re having trouble entering ketosis, try tracking your carb intake, ramping up your exercise, or following a few of the other tips provided above.

If you’re curious about trying the keto diet or experiencing challenges with entering ketosis, ask a doctor if ketosis is right for you.

How we reviewed this article:

SourcesHistoryHealthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

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Medically reviewed by Jared Meacham, PhD., RD, CSCS — Written by Ryan Raman, MS, RD — Updated on August 7, 2025

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Nutrition

How long does it take to enter ketosis?

How to tell whether you’re in ketosis

Ways to measure ketone levels

Why do some people take longer to enter ketosis?

What should you know before ‘going keto’?

Can you follow a keto diet if you’re a vegetarian or vegan?

Long-term health complications of the keto diet

Tips to achieve ketosis

Takeaway

How we reviewed this article:

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