The ketogenic diet is one of the most well-known low carb diets on the planet.
Despite its recent popularity, it has actually existed for over 100 years.
Originally, its purpose was medicinal. Before anti-epileptic agents existed, the ketogenic diet was introduced as a therapeutic nutrition plan to help treat children with epilepsy.
Today, this very low carbohydrate diet is primarily used to promote weight loss and manage blood sugar levels
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 of carbohydrates and increasing calories from fat helps your body switch its main fuel source from glucose — a type of sugar — to ketones, or compounds made by breaking down fat that serves as an alternative fuel source (
The result is a metabolic state where the body prefers fat as its primary fuel source (
While fans of the keto diet are quick to celebrate its health benefits, including weight loss, increased levels of HDL (good) cholesterol, and reduced blood sugar, insulin, and triglyceride levels, there are also drawbacks to this diet to consider before trying it (
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.
What’s more, 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.
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 (
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 around 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 it takes a week or longer to reach this state (
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 (
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 (
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 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 (
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 1.5–3.0 mmol per liter 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.
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.
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.
In a recent clinical trial observing the health benefits of the keto diet, researchers advised patients to consume less than 20 grams of carbohydrates per day, though other research cites a person on a ketogenic diet can consume between 20 and 50 grams of carbohydrates per day (
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 55–60 percent of their daily calories from fat, 30–35 percent from protein, and 5–10 percent 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 — a process that 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 dealing with any of the issues above.
It may take you longer to enter ketosis if you consume more carbs than are recommended, don’t eat enough fat, live a more sedentary lifestyle, or have difficulty getting enough sleep.
‘Going keto’ is considered a trendy 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.
Long-term health complications of the keto diet
Long-term side effects include fat buildup within the liver, kidney stones, inadequate protein levels, and vitamin deficiency, but 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 the increased consumption of fat.
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 (
Lastly, individuals living with diabetes and taking insulin or oral hypoglycemic agents can experience severe hypoglycemia if medications are not appropriately adjusted before initiating this diet. Individuals who have pancreas or liver conditions, or metabolism 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.
Despite the growing popularity of the keto diet, it has potential health consequences. Talk with your doctor before trying the keto diet.
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 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 increase ketone levels (
- Test your ketone levels regularly. Testing ketone levels can help give you an idea of whether you’re in ketosis — which lets you adjust your diet accordingly.
Following some of the tips listed above — such as tracking your carb intake or trying a short-term fast — may help you reach ketosis.
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.
Just One Thing
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.