The complete guide to ketosis
Ketosis has become an extremely popular topic recently, and it’s received its share of both praise and criticism. Is it healthy or harmful to be in ketosis? And if it’s beneficial, should everyone be doing it?
This guide provides all the information you need about ketosis, including its benefits, potential risks, and tips for successfully getting into ketosis and staying there.
1. What is ketosis?
Ketosis is a metabolic state in which your body uses fat and ketones rather than glucose (sugar) as its main fuel source.
Glucose is stored in your liver and released as needed for energy. However, after carb intake has been extremely low for one to two days, these glucose stores become depleted. Your liver can make some glucose from amino acids in the protein you eat via a process known as gluconeogenesis, but not nearly enough to meet the needs of your brain, which requires a constant fuel supply.1
Fortunately, ketosis can provide you with an alternative source of energy.
In ketosis, your body produces ketones at an accelerated rate. Ketones, or ketone bodies, are made by your liver from fat that you eat and your own body fat. The three ketone bodies are beta-hydroxybutyrate (BHB), acetoacetate, and acetone (although acetone is technically a breakdown product of acetoacetate).2
Your liver actually produces ketones on a regular basis even when eating a higher-carb diet. This happens mainly overnight while you sleep but usually only in tiny amounts. However, when glucose and insulin levels decrease on a carb-restricted diet, the liver ramps up its production of ketones in order to provide energy for your brain.
Once the level of ketones in your blood reaches a certain threshold, you are considered to be in nutritional ketosis. According to leading ketogenic diet researchers Dr. Steve Phinney and Dr. Jeff Volek, the threshold for nutritional ketosis is a minimum of 0.5 mmol/L of BHB (the ketone body measured in blood).3
Although both fasting and a keto diet will allow you to achieve ketosis, only a keto diet is sustainable over long periods of time. In fact, it appears to be a healthy way to eat that people can potentially follow indefinitely.4
Learn more about the keto diet
For more about the keto diet, check out this guide: A ketogenic diet for beginners and the videos below.
Does the brain need carbs?
There’s a long-standing yet misguided belief that carbs are necessary for proper brain function. In fact, if you ask some dietitians how many carbs you should eat, they’ll likely respond that you need a minimum of 130 grams per day to ensure that your brain has a steady supply of glucose.
However, this isn’t the case. In fact, your brain will remain healthy and functional even if you don’t eat any carbs at all.
Although it’s true that your brain has high energy demands and requires some glucose, when you’re in ketosis, there are plenty of ketones to supply a good portion of its fuel.5 Fortunately, your liver will always make the small amount of glucose your brain needs, even under conditions of complete starvation.6 This process, known as gluconeogenesis (literally “making new glucose”), can also provide glucose for other structures that need it, such as the red blood cells and a portion of the kidneys.
This system allowed our hunter-gatherer ancestors to go for long periods without eating because they had access to a fuel source at all times: stored body fat.
In truth, being in ketosis doesn’t have any adverse effects on brain function. On the contrary, many people have reported that that they feel sharper mentally when they’re in ketosis.7
2. Benefits of ketosis
In addition to providing a sustainable energy source, ketones – and in particular BHB – may help reduce inflammation and oxidative stress, which are believed to play a role in the development of many chronic diseases.8
Indeed, there are several established benefits and potential benefits of being in nutritional ketosis.
- Appetite regulation: One of the first things people often notice when they’re in ketosis is that they’re no longer hungry all the time. In fact, research has shown that being in ketosis suppresses appetite.9 One study looked at people who lost weight by following a ketogenic diet for eight weeks and then reintroduced small amounts of carbs. The researchers reported that levels of ghrelin (the “hunger hormone”) were suppressed in those who remained in ketosis, whereas those who were no longer in ketosis had higher ghrelin levels.10
- Weight loss: Many people automatically eat less when they restrict carbs and are allowed as much fat and protein as they need to feel full. Because ketogenic diets suppress appetite, decrease insulin levels, and increase fat burning, it isn’t surprising that they’ve been shown to outperform other diets intended for weight loss.11
- Reversal of diabetes and prediabetes:12 In people with type 2 diabetes or prediabetes, being in ketosis can help normalize blood sugar and insulin response, potentially leading to the discontinuation of diabetes medication.13
- Potentially enhanced athletic performance: Ketosis may provide an extremely long-lasting fuel supply during sustained exercise in both high-level and recreational athletes.14
- Seizure management: Maintaining ketosis with the classical ketogenic diet or less stringent modified Atkins diet (MAD) has been proven effective for controlling epilepsy in both children and adults who don’t respond to anti-seizure medication.15
There is also exciting early research suggesting that ketosis may be beneficial for many other conditions, such as reducing the frequency and severity of migraine headaches, reversing PCOS, perhaps enhancing conventional brain cancer therapies, possibly slowing down the progression of Alzheimer’s disease, along with potentially helping people live longer, healthier lives. Although higher quality research is needed to confirm these effects, much of the early research is very encouraging.
3. Nutritional ketosis vs. ketoacidosis
Nutritional ketosis and diabetic ketoacidosis are entirely different conditions. While nutritional ketosis is safe and beneficial for health, ketoacidosis is a medical emergency.16
Unfortunately, many healthcare professionals don’t really understand the distinction between the two.
Ketoacidosis occurs mainly in people with type 1 diabetes if they do not take insulin. In diabetic ketoacidosis (DKA), blood sugar and ketones rise to dangerous levels, which disrupts the blood’s delicate acid-base balance. People in ketoacidosis feel extremely ill and experience profound dehydration, vomiting, abdominal pain, and weakness. DKA requires hospitalization so that IV fluids and insulin can be given to gradually and safely lower blood sugar.17
In nutritional ketosis, BHB levels typically remain below 5 mmol/L. However, people in diabetic ketoacidosis often have BHB levels of 10 mmol/L or above, which is directly related to their inability to produce insulin. This graph shows the vast difference in the amount of ketones in the blood between ketosis and ketoacidosis:
When blood ketone levels rise beyond a certain level, a pancreas capable of making insulin will release enough to shut down further ketone production.18 By contrast, the pancreas of a person with type 1 diabetes cannot make insulin. So unless insulin is given via injection or IV, ketones will continue rising to life-threatening levels.
Other people who can potentially go into ketoacidosis are those with type 2 diabetes who take medications known as SGLT2 inhibitors, such as Invokana, Farxiga, or Jardiance.19
Also, in rare cases, women who don’t have diabetes can develop ketoacidosis while breastfeeding.20
However, for most people capable of producing insulin, it’s nearly impossible to go into ketoacidosis.
4. Tips for getting into ketosis
There are a number of ways you can get into nutritional ketosis safely and effectively.
- Reduce daily net carb intake to less than 20 grams: Although it’s possible that you may not need to be this strict, eating fewer than 20 grams of net carbs every day virtually guarantees that you’ll achieve nutritional ketosis. What does 20 grams of carb look like? Use our visual guide to find out, or simply try our keto recipes and meal plans that limit carbs to less than 20 grams per day.
- Try intermittent fasting: Going for 16-18 hours without eating may help you get into ketosis more quickly.21 This is easy to do by simply skipping breakfast or dinner, which may feel very natural on an appetite-suppressing keto diet.
- Don’t fear fat: Eating plenty of fat is a necessary and delicious part of ketogenic eating! 22 Make sure to include a source of healthy fat at each meal.
- Cook with coconut oil: In addition to being a natural fat that remains stable at high heat, coconut oil contains medium-chain fatty acids that can boost ketone production and may also have other benefits.23
- Exercise, if possible: During the transition into ketosis, you may not have enough energy to engage in vigorous physical activity. However, simply going for a brisk walk may help you get into ketosis more easily.24
Supplements not required
Note what’s not on the list above: you do not need expensive supplements, like exogenous ketones or MCT oil (medium-chain triglycerides). These supplements will likely not help you lose weight or reverse disease. At least there’s no evidence for that.25
People claiming huge benefits of these supplements – despite the lack of solid scientific support – may sometimes have a financial reason to believe in the supplements. Some of these products are sold under a multi-level marketing arrangement, where sales people are paid based on commission. For example, the company Prüvit sells drinkable ketones, called KETO//OS, with a multi-level marketing structure.
The salesperson might tell you that their product is fantastic and has changed his or her life and makes you lose weight, etc. But these benefits are basically unproven. Take all such stories with a grain of salt.
What these ketone supplements might do is possibly improve mental and physical performance for a short time. To the best of our knowledge, this potential and often mentioned benefit is also unproven. They do raise blood levels of ketones, an effect that can last anywhere from one to a few hours.
We’re not saying don’t buy these supplements. Perhaps you want to try them for yourself, and see how they make you feel. But you don’t need them to be successful on a keto diet or to get into ketosis. Here’s our big test of keto supplements:
5. Protein’s effect on ketosis
Although getting sufficient protein on any diet is important for preventing muscle loss, many questions have been raised about protein’s impact on ketone levels.
During digestion, protein is broken down into individual amino acids, which trigger the release of insulin. Although the amount of insulin needed to transport these amino acids into muscles is small, when large amounts of protein are consumed, the rise in insulin might potentially reduce ketone production to some extent.
For this reason, ketogenic diets for epilepsy are restricted in protein as well as carbs, which ensures that ketone levels remain elevated at all times.
However, protein’s effect on ketosis seems to be highly individual.
Some people do report that their ketone levels are significantly lower when they eat more than a modest amount of protein.28
By contrast, others may be able to eat quite a bit of protein without experiencing any changes in ketosis. For example, when Diet Doctor’s Bjarte Bakke conducted several n=1 experiments to see how much protein he could eat and still remain in ketosis, he found that keeping net carb intake below 20 grams per day was what ultimately mattered regardless of his protein intake.
Thus far, the scientific literature does not support the concern that too much protein worsens blood sugar control for most individuals. For instance, two studies showed a diet with 30% of calories from protein improved glycemic control.29 And another study found patients with type 2 diabetes eating a 50g protein meal had no significant increase in serum glucose concentration.30
If you want to stay in ketosis and still eat plenty of protein and are concerned about potential negative effects, it might be a good idea to conduct your own n=1 experiments in order to determine your personal protein threshold. It may be higher than you think.
6. What is optimal ketosis?
Getting into ketosis on a ketogenic diet is not a black or white thing. It’s not like you’re either in ketosis or out of ketosis. Instead, you can achieve different degrees of ketosis. The definition of “optimal” ketosis my vary depending on your goals. For instance, treating seizures may require a higher ketone level, whereas losing weight or improving blood sugar may depend less on the degree of elevation. This chart demonstrates this visually.31 The numbers below refer to values when testing blood ketone levels.
- Below 0.5 mmol/l is not considered “ketosis,” although a value of, say, 0.2 demonstrates that you’re getting close. At this level, you may not be at your maximum fat-burning zone.
- Between 0.5 – 3 mmol/l is nutritional ketosis. You’ll likely be getting a good effect on your weight and metabolic improvements.32
- Around 1.5 – 3 mmol/l is called “optimal” ketosis by some. However, the concept of optimal ketosis is controversial, and it’s unclear if it offers any substantial benefits over the 0.5-1.5 level. Exceptions could be treating seizures or those interested in maximum mental and physical performance gains.33
- Over 3 mmol/l is higher than necessary. It will probably achieve neither better nor worse results than being at the 1.5–3 level.34 Higher numbers can also sometimes mean that you’re not getting enough food (“starvation ketosis”).35 In people with type 1 diabetes, ketone levels over 3.0 mmol/L can be caused by a severe lack of insulin that requires urgent medical attention.36
- Over 8–10 mmol/l: It’s normally impossible to get to this level just by eating a keto diet. It means that something is wrong. The most common cause by far is type 1 diabetes, with a severe lack of insulin. Symptoms include feeling very sick with nausea, vomiting, abdominal pain and confusion. The possible end result, ketoacidosis, may be fatal and requires immediate medical care.
Here are the three reports from a 2-month experiment in reaching optimal ketosis:
- Experiment: Optimal ketosis for weight loss and increased performance
- Four weeks of a strict keto diet and ketone monitoring
- Final report: Two months of a strict keto diet and ketone monitoring
Do I have to reach optimal ketosis to experience the benefits?
In short, no. Many of the benefits, such as weight loss, are experienced at lower levels of ketosis (above 0.5 mmol/L).
However, you might need to reach higher levels of ketosis for high-level physical performance. There’s also a time element involved, it takes weeks or even a few months for the body to adapt completely. For more on this, here’s an interesting article from two of the top keto researchers in the world, Drs. Stephen Phinney and Jeff Volek:
7. Signs that you are in ketosis
There are several signs that suggest you’re in ketosis, although measuring your ketones is the only objective way to verify it. Here are the most common ones:
- Dry mouth or a metallic taste in the mouth.
- Increased thirst and more frequent urination.
- “Keto breath” or “fruity breath,” which may be more apparent to others than yourself. Learn more
- Initial fatigue, followed by an increase in energy.
- Decrease in appetite and food intake (one of the more welcome side effects!).
There are three ways to measure ketones, which all come with pros and cons. For a detailed comparison, see our full guide to the best way to test ketones.
For a shorter version, keep reading below. Note that we have no affiliations with any of the brands mentioned here.37
Urine strips are the simplest and cheapest way to measure ketosis. It is the first option for most beginners on a keto diet.
Dip the strip in your urine, and 15 seconds later the color change will show you the presence of ketones.38 If you get a high reading (a dark purple color), you’ll know that you’re in ketosis.
Con: Results can vary depending on how much fluid you drink. By drinking more water, you dilute the concentration of ketones in the urine and thus a lower level of ketones will be detected on the strips. The strips don’t show a precise ketone level. Finally, and most importantly, as you become increasingly keto-adapted and your body reabsorbs ketones from the urine, urine strips may become unreliable, even if you’re in ketosis.
This happens when the body becomes more adapted to using ketones, meaning that they increasingly stay in the blood to be used as energy instead of being lost through the urine. In one study, after 3 weeks the kidneys were found to excrete ketones at one third the rate, despite having the same blood ketone levels.39
Thus, the test may sometimes stop working – always showing a negative result – when you’ve been in ketosis for several weeks.
2. Breath-ketone analyzers
Breath-ketone analyzers are a simple way to measure ketones.40 At $169 and up they are more expensive than urine strips. But they are cheaper than blood-ketone meters in the long run, as they are reusable any number of times.
These analyzers do not give you a precise ketone level when used on their own, but provide a color code for the general level.41
You can also hook the device up to a computer or mobile phone (newer models) to get a more exact ketone number via the app. According to the manufacturer the device gives a decent correlation with blood ketones in most but not all situations.
Pro: Reusable, simple test.
Con: Does not always correlate well with blood ketones. Not always accurate, and can in some situations show entirely misleading values. For example, if you recently ate a lot of carbs, this can result in misleading high values on the Ketonix. More expensive than urine strips, and higher cost upfront than a blood meter.
Blood-ketone meters show an exact and current level of ketones in your blood.42 They are the gold standard and the most exact way to measure your ketosis level on a ketogenic diet. They used to be quite expensive, but now it’s possible to get cheaper test strips.43
Pro: Exact, reliable.
Con: Still expensive (at least $1 per test). Requires pricking your finger for a drop of blood.
What if you’re not in ketosis?
If you’re on a keto diet but aren’t seeing any signs or symptoms being in ketosis, here are a few strategies that may help:
- Track your carb intake. While we don’t recommend counting or tracking calories, it can be helpful to log your carb intake to make sure you’re truly eating less than 20 grams of carb. Use an online site or app, such as Cronometer, Senza, Carb manager, and others.
- Test blood ketones in the late morning or afternoon. Blood and urine ketones vary throughout the day, as well as from person to person.44 Many people find that their blood ketone levels are usually lowest right after waking up.45 Try testing later on, preferably a few hours after eating. Even if you’re only in ketosis for a portion of the day, you’re still getting some benefits, as discussed in this talk by Dr. Steve Phinney: Achieving and maintaining nutritional ketosis.
- Try to be patient. Although some people get into ketosis relatively quickly, it may take others a while.46 Unfortunately, people who are insulin resistant often seem to have a longer journey.47 Put in a solid month of consistent keto eating, and try to ramp up your physical activity, if possible. Within four weeks, you should definitely be in ketosis and experiencing its benefits.
Which is the best ketone meter on the market?
GuideWith a blood ketone meter, you can test for blood levels of ketones. Here’s our review of the top options.
8. Side effects, fears and potential dangers
Side effects typically happen within the first few days of starting a ketogenic diet and include headache, fatigue, lightheadedness, irritability, cramps, and constipation. These are known collectively as the “keto flu,” which can be remedied by managing fluids and electrolytes, among other things. Read more about the keto flu.
Is being in ketosis safe for everyone?
Being in ketosis is safe for most people, and it can provide many health benefits, including weight loss, optimal blood sugar and insulin levels, to name a few.
However, certain individuals should only follow a ketogenic diet under medical supervision, and others are best off avoiding it altogether.
Conditions that require medical supervision and monitoring during ketosis:48
- Type 1 diabetes
- Type 2 diabetes on insulin or oral diabetes medications
- High blood pressure on medication
- Liver, heart, or kidney disease
- History of gastric bypass surgery
Conditions for which ketosis should be avoided:
- Breastfeeding women
- Individuals with rare metabolic conditions that are typically diagnosed in childhood, such as enzyme deficiencies that interfere with the body’s ability to make and use ketones or to properly digest fats.49
The keto flu, other keto side effects, and how to cure them
GuideDuring the first few days of a keto diet, you can experience the keto flu. You can feel tired, have a headache, and be easily annoyed. Learn all about the keto flu and how to avoid it here.
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It’s estimated that under normal circumstances, the brain requires about 110-145 grams of glucose daily to function properly:
The physiology of ketone production and utilization has been well described in the medical literature. Below are 3 review articles that expand into more detail about the process
Dr. Phinney and Dr. Volek discuss the range of nutritional ketosis in pages 4-5 of their book The Art and Science of Low Carbohydrate Performance. Although this is based mostly on their clinical experience, and some may argue that even lower BHB levels may still represent adequate nutritional ketosis.
As a reminder, we may link to books and products such as the book above, but Diet Doctor will not benefit from your purchases. We do not show ads, use any affiliate links, sell products or take money from industry. Instead we’re funded by the people, via our optional membership. Learn more ↩
The main fear about lower-carb and higher-fat diets has been a possible increase in the risk of heart disease. However, interventional studies so far indicate that if anything, the risk appears to decrease:
- British Journal of Nutrition 2016: Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. [strong evidence for improved risk factors]
- PLoS One 2015: Dietary intervention for overweight and obese adults: comparison of low-carbohydrate and low-fat diets. A meta-analysis. [strong evidence for improved risk factors]
- Obesity reviews 2012: Systematic review and meta‐analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors [strong evidence for improved risk factors]
- Circulation 2010: Dietary intervention to reverse carotid atherosclerosis [moderate evidence for a reduction in atherosclerosis]
When carb intake is minimal or absent, during fasting or starvation, ketones can provide up to 70% of the brain’s energy needs:
This is mostly based on [anecdotal reports; very weak evidence]
Although one recent study showed improved neurocognitive function in AIDS patients when consuming a ketogenic diet↩
Journal of Medical Internet Research 2017: An online intervention comparing a very low-carbohydrate ketogenic diet and Lifestyle recommendations versus a plate method diet in overweight individuals with type 2 diabetes: a randomized controlled trial [randomized trial; moderate evidence]
Diabetes & Metabolic Syndrome 2017: Induced and controlled dietary ketosis as a regulator of obesity and metabolic syndrome pathologies [randomized trial; moderate evidence]
Some disagree with the use of the word “reverse” when it comes to type 2 diabetes. The concern is that it may imply the disease is completely gone, never to return. At Diet Doctor, we use the term “reverse” to indicate that the diagnosis of diabetes is no longer present at that moment. However, we acknowledge that the diagnosis of diabetes will likely return if a patient goes back to their prior high-carb eating habits. Therefore, “reverse” does not imply a forever cure. ↩
Frontiers in Endocrinology 2019: Long-term effects of a novel continuous remote care intervention including nutritional ketosis for the management of type 2 diabetes: A 2-year non-randomized clinical trial [weak evidence] ↩
Nutritional Neuroscience 2017: Short-term and long-term efficacy of classical ketogenic diet and modified Atkins diet in children and adolescents with epilepsy: A systematic review and meta-analysis. [systematic review of randomized trials; strong evidence]
Journal of Clinical Neurology 2015: Efficacy of and patient compliance with a ketogenic diet in adults with intractable epilepsy: a meta-analysis [systematic review of randomized trials; strong evidence] ↩
Although still somewhat controversial, several recent systematic reviews of randomized trials have failed to show a connection between eating saturated fat and increased heart disease risk:
Open Heart 2016: Evidence from randomised controlled trials does not support current dietary fat guidelines: a systematic review and meta-analysis [strong evidence]
Nutrition Journal 2017: The effect of replacing saturated fat with mostly n-6 polyunsaturated fat on coronary heart disease: a meta-analysis of randomised controlled trials
[strong evidence]Learn more here: A user guide to saturated fat ↩
The Journal of Nutrition and Metabolism 2018: The effect of medium chain triglycerides on time to nutritional ketosis and symptoms of keto-induction in healthy adults: a randomised controlled clinical trial [randomized trial; moderate evidence]
British Journal of Nutrition 2015: The role of dietary coconut for the prevention and treatment of Alzheimer’s disease: potential mechanisms of action [overview article; ungraded] ↩
As far as we know there are no high-quality studies (RCTs) that test these supplements and determine their health effects, beyond raising ketone levels. Here is a recent review:
Exogenous ketone supplements do raise ketone levels in the blood:
One study of MCT oil for mild cognitive impairment is sometimes mentioned, but it did not show any clear effect. Out of only six participants two quit during the study, one saw some improvement and one got worse:
BBA Clinical 2015: Pilot feasibility and safety study examining the effect of medium chain triglyceride supplementation in subjects with mild cognitive impairment: A randomized controlled trial [very weak evidence] ↩
As far as we know there is no good reason to believe this to be the case, and no studies to demonstrate it. ↩
An indirect benefit could be possible – if the supplements result in less hunger, they could reduce food intake and potentially aid weight loss. This theory would have to be tested, and as far as we know it has not been tested. ↩
The chart is from the book The Art and Science of Low-Carbohydrate Performance by Professor Stephen Phinney and Jeff Volek. However, these definitions of ketone ranges aren’t based on clinical trials but rather a compilation of clinical opinion.
The levels of the fat-storing hormone insulin will probably be relatively low, as low insulin levels are normally required for ketosis. ↩
The scientific evidence for the mental and physical benefits of this is not strong. Even though 1.5-3.0 mmol/L is considered “optimal” by some, achieving this BHB level isn’t necessary for weight loss and blood glucose control. ↩
Sustained levels above 3.0 or 4.0 mmol/L may occasionally occur in some people following a ketogenic diet, but they’re more often seen in starvation ketosis, which occurs after fasting for several days. ↩
Seek immediate medical attention if you have type 1 diabetes and experience ketone levels over 3.0 mmol/L. ↩
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The strips measure the ketone acetoacetate. The presence of this in your urine indicates that you’ve been in ketosis during the hours before testing. ↩
Breath analyzers measure the ketone acetone. ↩
For example, the Ketonix meter reflects the following levels of acetone:
- Blue – negative
- Green – mild ketosis
- Yellow – moderate ketosis
- Red – deep ketosis
Blood-ketone meters measure the ketone beta-hydroxybyturate (BHB). ↩
One study found that urine ketone levels tended to be highest in the morning and after dinner:
These conditions are based on clinical expertise and clinical concern, and therefore, this list may not be all inclusive ↩