How Long Does It Take to Enter Ketosis?
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 triglycer >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.
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 sa >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.