How Long It Takes to Enter Ketosis: 24-Hour Window and First Few Days (2024)

A ketogenic or keto diet consists of high fat, moderate protein, and very low carbs. People adhering to a strict keto diet eat fewer than 50 grams (g) of carbs per day, forcing the body to start using fat-derived ketones for energy instead of glucose (sugar) derived from carbs. This state is called ketosis. Getting into ketosis takes anywhere from two to four days, on average. To enter ketosis, roughly 70–80% of daily calories should come from fat, less than 10% from protein, and only about 5% from carbohydrates or "carbs." Intermittent fasting before starting a keto diet can help speed up the process of getting into ketosis.

Read on to learn what you need to know about getting into ketosis, the timeline of ketone effects, what you can and cannot eat on a keto diet, signs you're in ketosis, ways to get into ketosis faster, and potential risks of staying on a strict keto diet for extended periods.

How Long It Takes to Enter Ketosis: 24-Hour Window and First Few Days (1)

Getting Into Ketosis: Timeline of Ketone Effects

The human body's metabolism uses glucose for energy (glycolysis) before it uses fat. Therefore, sugar molecules from carbohydrates that are stored in the body as glycogen must be depleted before ketosis starts. Without stored glycogen (sugar) to burn as fuel, your body enters ketosis as it gradually switches from using glucose for energy to using fat as fuel.

There isn't a one-size-fits-all formula for determining exactly how many daily carbs make the difference between entering ketosis or not. That said, eating fewer than 50 grams of carbs a day is generally considered a ketone-producing diet. Full keto-adaptation, in which your body makes fat its preferred source of fuel during physical activity, can take a few weeks or even months.

The ketosis timeline can vary greatly depending on various factors, such as:

  • The amount of glycogen stored in reserve when someone starts a keto diet
  • Age (younger people get into ketosis faster)
  • Body weight
  • Exercise habits
  • Basal metabolic rate

Certain illnesses that affect the thyroid (hypothyroidism) can slow metabolism and influence how long it takes to get into ketosis. Ketogenic diets may induce a shift in how the thyroid functions.

Older adults and people with health issues that slow their metabolic rate typically take longer to get into ketosis. Always speak to a healthcare provider before starting a ketogenic diet, especially if you have underlying medical conditions.

The precise timeline for fat loss on a keto diet isn't set in stone and varies from person to person. During the first 24-hour window and the next few days on a keto diet, most weight loss is from water, not fat. Hypothetically, ketosis-induced fat loss kicks in when the body starts burning fat deposits for energy. There is mixed evidence and ongoing debate about the fat-burning superiority of keto diets compared to other weight loss plans.

Getting into ketosis and losing weight on a ketogenic diet is a complex metabolic process; more research is needed to fully understand how it works.

Seeing a Nutritionist

If you're thinking about starting a regimented keto diet at home, talk with a healthcare provider and consult with a registered dietitian (RD) or registered dietitian nutritionist (RDN) before going on a dayslong fast or making radical changes to the amount of carbs, fats, or protein you're eating every day.

Signs You're in Ketosis

Signs of ketosis range from flu-like symptoms to "keto breath." The easiest science-based way to know if you're in ketosis is a simple home test using a ketone urine strip. Any color (from pink to purple) on the ketone test strip indicates ketosis.

Symptoms of carbohydrate withdrawal that may be signs you're entering ketosis include:

  • Accelerated weight loss
  • Bad breath (halitosis)
  • Changes in appetite
  • Constipation or diarrhea
  • Dehydration from body water loss
  • Dizziness
  • Fatigue
  • Headache
  • Irritability
  • Gastrointestinal distress (stomach issues)
  • Ketones in the bloodstream and urine
  • Muscle cramps
  • Muscle weakness
  • Sluggishness
  • Subpar exercise performance in the first few days/weeks

Is There a Way to Get Into Ketosis Faster?

Fasting for 12 hours is the fastest way to get into ketosis. When you're initiating a very low-carbohydrate ketogenic diet, the fewer carbs you eat in the first 24 hours and the next few days, the more quickly your glycogen reserves will get depleted and the faster you'll get into ketosis.

Medium-chain triglyceride (MCT) oil supplements may help you get into ketosis faster. In 2018, a study found that keto-induction was quicker with MCT supplementation. Within the first 24–72 hours of initiating a keto diet, the researchers found that when study participants got 80% of their calories from fat, 13-17% from protein, and 3-6% from carbohydrates—and also took MCT oil—they'd get into ketosis more rapidly than people on the same keto diet who didn't take supplemental MCT oil.

Ketosis and Diet: What's Safe and Possibly Dangerous?

It's difficult to answer the question, "Is ketosis dangerous?" with scientific certainty. Most studies on what's safe and possibly dangerous regarding ketosis and keto diets are of low quality and don't have large sample sizes.

Due to a lack of sufficient high-quality clinical evidence that shows keto diets to be safe and without potential danger, there are ongoing debates about whether the benefits of very low-carbohydrate ketogenic diets that are extremely high in unhealthy fats outweigh their risks.

In general, current research shows that being on a strict keto diet and in ketosis for about 8-12 weeks is safe. After 12 weeks, potential risks and possible dangers tend to increase. Although this topic remains controversial, accumulating evidence suggests that for most people, the long-term health risks of very low-carbohydrate ketogenic diets outweigh the advantages.

Long-term adverse effects of being in ketosis for extended periods may include:

  • Micronutrient deficiencies (insufficient vitamins and minerals)
  • Electrolyte abnormalities
  • Poor cholesterol profiles (too much “bad” LDL cholesterol)
  • Increased risk of heart disease
  • Increased risk of chronic kidney disease
  • Kidney stones (renal calculi)
  • Hypoproteinemia (not enough protein in the blood)
  • Decreased bone mineral density (osteoporosis)
  • Copper-deficiency anemia
  • Iron-deficiency anemia
  • Ketoacidosis (acidic blood from too many ketones)
  • Selenium-deficiency cardiomyopathy
  • Hepatic steatosis (non-alcoholic fatty liver disease)

Research suggests that eating a low-carbohydrate ketogenic diet during pregnancy increases the risk of neural tube defects in newborns, even when taking folic acid supplements.

Ketogenic diets are usually high in red meat, processed meats, and saturated fats, which are associated with an increased risk of chronic kidney disease, heart disease, atherosclerosis (plaque buildup in arteries), cancer, diabetes, Alzheimer’s disease, and other illnesses. Additionally, keto diets are low in health-protective foods such as fruits, vegetables, legumes, and whole grains.

Summary

Ketosis is a metabolic state marked by your body using fat for fuel. When someone's not on a ketogenic diet, the sugar molecules (glucose) derived from carbohydrates are the body's preferred energy source. On a stringent low-carbohydrate keto diet, the body is starved of carbs, which forces it to turn fat into ketones, which are used as fuel instead of glucose.

Getting into ketosis takes about two to four days, on average, because that's how long it takes for glycogen reserves to be depleted after someone starts eating a keto diet with under 50 grams of carbs per day. Fasting, limiting carbs, and MCT oil supplements can speed up the ketosis timeline.

How Long It Takes to Enter Ketosis: 24-Hour Window and First Few Days (2024)

FAQs

How Long It Takes to Enter Ketosis: 24-Hour Window and First Few Days? ›

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.

Can you go into ketosis on a 24 hour fast? ›

Fasting for short periods

Intermittent fasting (IF) can help a person reach a state of ketosis. In some controlled cases, a doctor may recommend fasting periods of 24–48 hours , but most people do not need to fast this long to reach ketosis.

How fast can you get back into ketosis after a cheat day? ›

If you've cheated on keto, you're likely out of ketosis. Once out, you'll need to strictly follow the keto diet to reenter ketosis. This process takes several days to 1 week, depending on your carb intake, metabolism, and activity levels ( 6 , 7 , 8 ).

What day is the hardest when starting keto? ›

Pro tip: If possible, I recommend starting the keto diet on a Thursday, as days 3 and 4 are usually the hardest part of the transition.

What is the longest it can take to get into ketosis? ›

The time it takes to reach ketosis varies from person to person, typically ranging from two to eleven days. How long you will take to get there depends on several factors such as your carbohydrate intake, physical activity, age, and more.

How much weight can you lose in a 24-hour fast? ›

Be patient with the scale. The day after the fast, you will see the number on the scale drop significantly (anywhere from one-half to three pounds). [6] While much of this is water weight, you still lose fat.

What puts you in ketosis fastest? ›

Fasting for 12 hours is the fastest way to get into ketosis. 3 When you're initiating a very low-carbohydrate ketogenic diet, the fewer carbs you eat in the first 24 hours and the next few days, the more quickly your glycogen reserves will get depleted and the faster you'll get into ketosis.

Is it bad to go in and out of ketosis? ›

Because keto cycling is so new, no studies have examined the benefits and risks yet. Kieffer says cycling in and out of ketosis — eating carbs then not eating carbs — might be dangerous.

How long until ketosis kicks in? ›

How long does it take to get into ketosis? If you eat between 20 and 50 grams of carbohydrates each day, it will usually take you two to four days to enter ketosis. However, the time it takes to enter this state varies based on several factors. It may take you a week or longer to get into ketosis.

What time of day is ketosis highest? ›

These results indicate that ketonuria in subjects with stable ketosis is highest and can be most reliably detected in the early morning and post-dinner urine.

On what day of keto do you start losing weight? ›

Weight loss from keto varies from person to person. Generally, if you maintain a daily caloric deficit of around 500-700 calories, you can expect noticeable weight loss after anywhere from 10 to 21 days. However, remember that weight loss is not linear and some may see results sooner.

What week do you lose the most weight on keto? ›

If a person follows the 75% fat /20% carb/5% fat keto diet, average results may look like this:
  • Weeks 1–2: rapid weight reduction phase due to water loss – up to ten pounds.
  • Weeks 2–4: standard weight reduction – between one and two pounds per week.
  • After the first month – slow weight loss – around one pound per week.
Mar 6, 2022

How to speed up weight loss in ketosis? ›

To maximize weight loss on a ketogenic diet, get adequate sleep, reduce stress, be more active and consume whole, nutritious, low-carb foods whenever possible.

Why am I not in ketosis with no carbs? ›

#1: Not enough time

If you're doing everything right but not in ketosis, you may simply need more time. Getting into ketosis isn't like cooking a roast. You don't just set the oven at 275 degrees for 2 hours, go watch a movie, and come back to a perfect result. Your body is unlike any other body.

What is the best exercise to get into ketosis? ›

Instead, try incorporating a variety of low intensity, steady state activities into your workout routine to get the most bang for your buck on the ketogenic diet. Jogging, biking, rowing, and doing yoga are just a few examples of physical activities that may be especially beneficial on keto.

Will a 2 day fast put me in ketosis? ›

A 72-hour fast, or fasting for three consecutive days without any food intake, can help your body enter a state of ketosis. Ketosis is a metabolic state in which your body burns stored fat for energy instead of glucose from carbohydrates.

Is fasting for 24 hours good for you? ›

Longer periods without food, such as 24-, 36-, 48- and 72-hour fasting periods, are not necessarily better for you, and may be dangerous. Going too long without eating might actually encourage your body to start storing more fat in response to starvation.

Can I break a fast and stay in ketosis? ›

You can then decide whether to consume them during or between fasting periods. During a fast, choose calorie-free beverages and supplements, if any. Some people choose to eat small amounts of certain foods to curb cravings, which may break your fast but still keep you in ketosis.

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