The ketogenic diet is one of the most popular low-carb diets on the planet.

It helps your body switch its main fuel source from glucose — a type of sugar — to ketones — compounds made by breaking down fat that serve as an alternative fuel source (1).

A ketogenic diet not only helps you lose weight but is also linked to numerous benefits, such as increased levels of HDL (good) cholesterol and reduced blood sugar, insulin, and triglyceride levels (2, 3).

However, some people find that it takes them much longer to enter ketosis than others. What’s more, many struggle to enter ketosis in the first place.

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

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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 source of energy when glucose — a type of sugar —is limited (4).

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

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 (5).

The time it takes to enter ketosis varies from person to person (6, 7).

In general, it takes 2–4 days if you eat 20–50 grams of carbs per day. However, some people may find it takes a week or longer to reach this state (6, 7, 8).

Some factors that can affect how long it takes to enter ketosis include your typical daily carb intake, your daily fat and protein intake, exercise, your age, and your metabolism.

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 (5).

Summary It typically takes 2–4 days to enter ketosis if you eat fewer than 50 grams of carbs per day. However, some people may take longer depending on factors like physical activity level, age, metabolism, and carb, fat, and protein intake.

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, (5).

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 (9, 10).

Urine testing strips are a cheap and simple way to tell whether you're in ketosis. However, they aren’t 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 (11).

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 (12).

A blood ketone level above 0.5 mmol indicates that your body is entering ketosis. That said, a blood ketone range of 1.5–3.0 mmol per liter is ideal for maintaining ketosis (8, 13).

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

Summary You can tell whether you’re in ketosis by looking for symptoms or testing your ketone levels with a breath meter, urine sticks, or a blood ketone meter.

There are many reasons why some people take longer to enter ketosis than others.

In most cases, it’s due to unintentionally eating more carbs than recommended for a ketogenic diet. Eating too many carbs can stop your body from producing ketones.

It’s worth noting that some people can enter ketosis while eating a higher number of carbs (up to 90 grams per day), while others need to eat fewer — as low as 25 grams per day (14).

Therefore, you may need to further reduce your carb intake if you’re struggling to enter ketosis.

Another common mistake is not eating enough fat on a ketogenic diet. In general, people should aim to consume at least 70% of their daily calories from fat, 20% from protein, and the remaining 10% from carbs (15).

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 — a process that converts amino acids from protein into sugar. Too much sugar can stop your body from producing ketones (16).

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

For example, exercise helps your body empty its carb stores faster. Thus, people who exercise more may enter ketosis faster (17, 18).

If you struggle to get into ketosis, check whether you’re making any of these mistakes.

Summary It may take you longer to enter ketosis if you eat too many carbs, don’t eat enough fat, don’t exercise enough, or don’t get enough sleep.

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

  • Eat 20–50 grams of carbs per day. This should encourage your body to produce ketones. People who struggle to enter ketosis may need to stick to the lower end of the scale (14).
  • Track your carb intake. This helps to ensure you eat 20–50 grams of carbs per day and don’t underestimate your carb intake.
  • Avoid eating out. While there are many keto-friendly restaurants, eating out makes it harder to track your carbs.
  • Be aware of hidden carb sources. It's easy to overlook condiments, but many sauces and dressings are high in carbs.
  • Increase your intake of high-quality fats. Aim to get at least 70% of your calories from healthy fats, such as nuts, nut butter, extra virgin olive oil, coconut oil, avocado oil, avocados, meats, eggs, and fatty fish like salmon.
  • Try a short-term fat-fast. A short-term, high-fat fast — such as an egg fast — can help you get into ketosis faster, as it’s very low in carbs and high in fat.
  • Try intermittent fasting. Fasts like intermittent fasting may help your body shift its fuel source from carbs to fat while maintaining its energy balance (19).
  • Use a medium-chain triglyceride (MCT) supplement. MCTs are a type of fat that’s rapidly absorbed by your body and easily converted into ketones (7, 20).
  • 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 increase ketone levels (17, 18).
  • Test your ketone levels regularly. Testing ketone levels helps give you an idea of whether you’re in ketosis — which lets you adjust your diet accordingly.
Summary Following some of the tips listed above — such as tracking your carb intake or trying a short-term fast — may help you reach ketosis.

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 struggle to enter ketosis, try tracking your carb intake, ramping up your exercise, or following a few of the other tips provided above.